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Artwork by Gemsom_AO3 on Twtter
The darkness was often overwhelming at sea, and Izuku was increasingly grateful that the moon was nearly full. Still, he lifted an oil lamp to illuminate the rig as he double checked the knots. Green eyes flickered meticulously over each of the ropes tied tight around the mast. They were always there in case of siren attack. The entire crew would be tied down at the first hint of siren song, and the ropes would have to hold until the luring calls ended. The ship was tall enough to be less than ideal for the sirens, and none had ever called to the crew in all the time that they’d been sailing across the narrow sea. Men had been killed in siren attacks on this channel before, but most of the men believed that their particular route was safe.
Izuku knew better.
He checked each rope diligently but winced at the texture. The ropes were rough spun and coarse despite being soaked through. It would help keep the knots together, but it had also contributed to Izuku’s growing collection of calluses. Still, he checked every rope - something he was sure the other men didn’t. Confident that he’d already fulfilled the most important of his night’s watch duties, Izuku made his way to the very front of the ship. Despite the echoing quality of sound on the ocean, the starboard railing nearest the figurehead offered some privacy. Everyone’s sleeping quarters were at the back of the ship; where there was less motion and noise to disturb them. Izuku sat down and slid his legs through the railing so that they could dangle over the side of the ship. He rested his head against the sturdy wood of the rails and watched the light of his lantern shine off the inky, black waves. He had no way of knowing whether his siren would return tonight. Izuku had been part of the crew for nearly two years, and Kacchan had been visiting him since the very beginning. The siren always seemed to find him when they traveled over this stretch of ocean. He came in the dead of night; the most dangerous time for any man on watch. As the newest member of the crew, Izuku was always given the worst watch duty, and so he’d been standing there in the dark on unsteady legs the first time he saw the siren. He should have woken someone then, but he’d still been new. He was afraid someone would gut him over a false alarm.At least, that’s what he told himself. It was far too dangerous to admit that he’d been enthralled at the first glimpse of burnt orange and black scales. Of course, it was the fear that Izuku would never see the siren again that kept him from mentioning it the following morning or even weeks later. The siren was beautiful in a way that Izuku couldn’t describe. He was mesmerizing. Katsuki moved with the easy grace of any large predator. His humanoid half was a believable shape, but his features could never have been mistaken for human. His face was unnaturally symmetrical with high cheekbones and a sharp jawline. In contrast, his lips appeared soft, but his mouth was full of needle, sharp teeth.Both halves of his body were sleek and muscular. Izuku had thought about taut muscle and the shimmer of sleek scales far too often. The way the deep ‘V’ of Katsuki’s hips melted into scale was nothing less than artful. Izuku had never gotten a good look at the siren’s full length, but he knew the fins were fanned and spined.Moreover, Katsuki’s eyes were the most vibrant, red color that Izuku had ever seen. They were so bright that he hadn’t even noticed the shock of pale blond hair at first.For months after their first meeting, the siren had watched Izuku soundlessly while the human kept himself tied to the rail, but that caution eased as soon as Izuku learned that they could communicate. They didn’t share a language, but, when Katsuki vocalized, Izuku got an impression of what he was trying to convey. It was an impossibility that Izuku couldn’t even hope to explain. Katsuki released clicks, whistles, and trills, but each sound would lay a suggestion over Izuku’s thoughts. The more often they visited, the more clearly Izuku could understand. Soon, Katsuki’s vocalizations were as clear as the spoken word, and they were talking at length during the darkest hours of the night. Still, Izuku had to be cautious. Just because the song had never come, didn’t mean it wouldn’t. Katsuki never hid his nature. He didn’t offer any reassurances, but at least he wasn’t a liar. Izuku had little doubt that Katsuki would eat him if he dropped his guard. Katsuki wasn’t shy about asking Izuku to give up everything and slide under the waves with him.Izuku was beginning to suspect that all sirens lured sailors with false friendship. It wouldn’t explain the stories of entire ships cleared in the night, but it would explain Katsuki’s persistent attention.As though summoned by the thought alone, Izuku caught the faintest glimmer of movement in the water. He drew up his legs, just in case it was an unexpected visitor. Izuku felt himself involuntarily calm as pale skin rose from the water. In the bright light of the moon, Katsuki stood out easily among the waves. He stared up at Izuku with cunning, red eyes and grinned. He shifted until he swam on his back, and his expression quickly became smug.He knew just how much Izuku longed to see the length of the siren’s body.He was long and muscular with full, wide fins. Most of it glittered black and lovely, but there were a few patterns of burnt orange among the scales. Izuku was near certain they would have a serpentine glint of green if he ever saw the predator in sunlight. “Deku,” The siren greeted.It was a miracle to Izuku that the creature could combine the feeling of saying his name with an insult. It had been his first clue that the sirens were frightfully clever. Any tales of mindless, bloodthirsty monsters had been put to rest. “Kacchan,” Izuku answered. It was his own spin on Katsuki’s name with a childish sweetness. He’d invented the name just to spite the siren at first, but now it rolled off his tongue with affection. “What happened?” Katsuki clicked in response. Crimson eyes narrowed darkly as the siren considered the human on deck.Izuku’s eyes narrowed in turn. That was another thing - Katsuki always seemed to know more than he should. It couldn’t just be perception. Izuku knew he had an expressive face, but Katsuki seemed to read his soul at a glance. He always knew when Izuku was sad or cheerful, and he had an uncanny ability to pick up spikes in his depression.Silence stretched between them. It grew tense and uncomfortable, but Katsuki refused to break it. Sharp eyes never seemed to leave Izuku, even as the choppy waves battered the siren against the surface. “My mother is… Very unwell,” Izuku finally answered; against his better judgment. The last thing Katsuki needed was more ammunition. The siren knew that his mother had been frail for a long time, but now her sickness had taken a turn for the worse. The siren made a low cooing sound; one of comfort rather than a statement. Izuku had lost his father years ago. They sold their little house to pay off his remaining debts. When his mother grew sick a few years later, Izuku had left boyhood behind to sail with Nemuri Kayama. It was a dangerous job, but it paid well enough to afford his mother’s medication. “Tell me how you always know,” Izuku requested. He leaned more heavily into the railing and released a low sigh. Talking with Katsuki was always dangerous. Even now, he was forgetting the cold of the air, the itch of the salt on his skin, and the discomfort of the sturdy wood under him.The siren huffed at him. He might as well have told Izuku to piss off, but the sailor was getting tired of answering Katsuki’s questions without getting any answers of his own. “I could leave, Kacchan. There’s nothing here forcing me to talk to you,” Izuku reminded. He’d only slunk to this tactic a couple of times before. It got Katsuki too worked up, and Izuku was afraid the siren might stop visiting him if he kept upsetting him. “You’d miss me too much,” Katsuki hissed back. His eyes were angry, ruby slits. His fins fanned with disapproval. Izuku could swear the orange scales were brighter in Katsuki’s rage, but that was probably just because his threatening displays were effective. “The only one gaining anything here is you, Kacchan. I love talking to you, but we both know it’s bad for my health,” Izuku answered. He kept his voice cold. It made something ache deep in his chest, but he had to learn to do better. Katsuki wasn’t here out of affection. At best, he was curious, and, at worst… Izuku’s face must have fallen with the painful thought, because Katsuki decided to yield.“It’s your glow… It’s darker than I’ve ever seen it,” Katsuki answered. His vocalizations sounded gentler than usual - almost apologetic. When Izuku lifted his head again, he could see that Katsuki’s expression had softened with concern.
Was any of that concern real?
“Auras? Is that how sirens choose?” Izuku asked. He didn’t need to explain ‘for what.’ It wasn’t the first time Izuku had tried to ask Katsuki about his kind’s interest in human flesh. “The bluer the soul, the less someone has to live for. You glow like a soul who would willingly join me in the water… But that isn’t why I’m here,” Katsuki growled. The words seemed more difficult for him. Some of the thoughts rose as rumbling vibrations from the pit of his chest. Izuku lowered his head again. He had a blue soul? And that was supposed to mean that he didn’t want to live as much as everyone else? That couldn’t be true. Izuku wanted to live. He wouldn’t give it up for anything; not even Kacchan. But it was true that there wasn’t much left to tether him. His mother would be gone soon. There was nothing left that could stop it. He spent so much time at sea that he had no real friends left. Even Captain Kayama’s crew was mostly older and tight-knit, which often left Izuku the odd one out. It didn’t mean he would ever give up.Izuku’s head thunked against the railing again. Somehow knowing made it worse. Katsuki released a garbled trill. It was loud enough that Izuku worried they’d be heard by the crew, but he didn’t bother to admonish the siren. Izuku was used to it. The same loud trill always preceded the words that haunted Izuku’s every waking thought.
“Offer your life to me, Izuku.”
The intention was so clear that Izuku felt them thrum through his being. They hollowed his chest until every breath felt raspy and cold. Sirens were cruel in a way the stories could never capture. A hypnotic song was so much kinder than this.But even a fake friendship was better than none. “Couldn’t you just sing me into the water like they say in all the stories?” Izuku asked. His voice was little more than a whisper, but, however low he spoke, Katsuki always seemed to hear it. “You have to come of your own free will,” Katsuki answered. His noises had softened again, but Izuku had to assume the creature was mimicking him rather than feeling genuine regret. “What if I told you I was never coming? Would you give up?” Izuku asked. His fingers tightened against the railing until it hurt. His knuckles were already pale with the cold, and now they were white with the pressure. “Never. As many times as I sense you near, I will be by your side,” Katsuki answered. His lips spread in a smirk that was full of sharp teeth. Somehow, Izuku still found it charming. “Tell me something new about the world under the waves if you want me to join you so badly,” Izuku ordered.
His heart still hurt.
His siren wasn’t forgiven, but, even if the desire to drown and consume were part of Katsuki’s nature, Izuku still wanted to talk. For hours more, Katsuki entertained him with another story of undersea wildlife, but, as always, he wouldn’t talk about the other sirens.
----- CHAPTER BREAK -----
If Izuku’s soul was blue before, it must be nearly black now. Thoughts of dark, ocean water swirled in his head. For once, they were welcome, if only because they drowned out the terrible thoughts lurking just beneath their surface. Everything was over for him.When the crew returned to their home port, Izuku found that he had no home to return to. His mother had passed while he was at sea. With no one there to make the arrangements, the city had cremated her, and his charming neighbors had torn their home apart and taken anything of value that remained. Izuku didn’t have a home anymore. No mother. No friends. No one in his neighborhood had been able to look him in the eye as he walked by, and so he knew that not one person had stood up for him.He wondered if any of his mother’s friends had been there for her final moments; if they’d waited for her to go cold before pilfering all they could. He couldn’t even find it in his broken heart to be angry with them. They lived in the slums. Sometimes, cruelty was about survival - not hatred. His thoughts drifted to Katsuki again. The siren didn’t seem to hate him. Maybe his kind had needs that Izuku couldn’t understand. Izuku’s fingers shook. He tightened his grip on his travel bag, which now held everything he owned. It was time to go back to the ship. Maybe he’d find a new home on the other side of the sea, where the memories of his childhood couldn’t haunt him. His feet felt heavy as he ambled toward the port. It was unlike him to return to the ship so early, but he was sure Captain Nemuri would let him stay in his bunk until they left again. He certainly wasn’t going to sleep in his former home. Izuku trudged his way up the ramp to the ship and was surprised to find that Nemuri was already there, and she wasn’t alone. She stood speaking to a young man. The newcomer looked as exhausted as Izuku felt. His hair was shaggy and dark purple to match his eyes. He looked disheveled, as though he hadn’t properly rested or groomed in some time. There were noticeable bags under his eyes, and his fingers were gripped tightly around a thick, canvas bag. Was he a new member of the crew?“Midoriya, this is Shinsou,” Nemuri introduced with a wide smile. She put a hand on her hip and crossed her arms over her chest. “A friend of mine asked me to take him in, and I was hoping you could show him the ropes.” “Of course,” Izuku answered automatically. His voice sounded tight and strained even to his own ears. He hoped Shinsou wouldn’t take it too hard. It had nothing to do with teaching him, and everything to do with the grief and despair darkening his soul. “He’s going to share your bunk area, and you’ll share duties for this voyage,” Nemuri explained. She stepped forward and gently patted Midoriya’s shoulder. “Since you’re here, would you mind helping him get settled in? I have some business to take care of in town.”She sounded rushed but not displeased. It must have been a welcome favor and a good friend who asked. The request wasn’t a brush off either, as Midoriya had begun to fear. Shinsou must be important to someone, and Izuku was being entrusted with his care. Whatever else was going on, he couldn’t fail his captain, and maybe it would be good for him to have a distraction.“Sure,” Izuku answered. His smile became just a little more genuine.As Nemuri wandered away, Shinsou was left watching him with a strange mixture of distrust and nonchalance. Midoriya hiked his bag further up on his shoulder and made his way toward the stairwell that would take them beneath the deck. “Come on, Shinsou. I’ll show you where we sleep.” The young man followed him stiffly as Izuku traveled the worn steps. He paused at the bottom to make sure Shinsou didn’t slip, and then led him down the hall to their cabin. It was the smallest of them all, but there were two, distinct bunks.Izuku had it to himself for a long time. It was cramped, but they could make it work as long as they didn’t actively try to make each other miserable. Shinsou set his bag on the floor and crawled into the unoccupied bunk. “I can show you around if you’re up to it? Or we could take a break. We’ll be docked for a couple of days yet if you have anything you need to do in town,” Izuku suggested. Shinsou’s body stiffened as he was addressed. His eyes narrowed as he turned to face the wall. “Don’t worry about it. I’m not here to make friends,” Shinsou answered. Izuku sighed softly. Maybe not making each other miserable had been too much to hope for. What was wrong with him? Not even a total stranger that was dependent on him wanted his company.Izuku might have tried connecting again, but he didn’t have the energy. He slid into his own bunk and tried to sleep. The tension in the room was thick, but neither of them bothered the other. Shinsou was mostly quiet for their remaining few days at port. Izuku wished that he could have gotten to know Shinsou a little better. He probably should have been grateful for the separation, but the silence inevitably allowed his mind to wander.That was dangerous when his thoughts lingered in dark places. It took everything he had to hide his crying, especially since Shinsou didn’t seem to be sleeping any better than Izuku was.Shinsou didn’t even try to leave the ship before departure. It couldn’t have been easy for him to ignore Izuku the entire time, and it was awkward to say the least. Tensions were high by the time the ship left port. Fortunately, something inside Izuku eased as soon as they’d left dry land behind them.He worked harder than usual, because this was the only place he really belonged anymore. He explained their daily work to Shinsou with endless patience. Izuku showed him how to do everything over and over again - even when the other sailors made comments about how unusually green their newbie was. Izuku wished they wouldn’t whisper about their aversion to “babysitting.” Izuku was the one teaching Shinsou everything anyway. Shinsou wasn’t friendly, but he was hard working. Izuku was sure to let him know it, and the tension between them seemed to ease. By their first night watch together, Shinsou had loosened up considerably. Izuku passed by the mast and checked the ropes. He glanced over at Shinsou and offered him a soft smile. “What are the ropes for?” Izuku prompted. “Sirens,” Shinsou answered immediately. “Captain Kayama swears there’s a pod of them out here somewhere.” He glanced nervously toward the dark water. Good. It was better that he had a healthy fear of it. “Won’t it be too late for us if they decide to attack?” Shinsou continued. He fingered the lines nervously, but he didn’t look Izuku in the eye as he asked. Izuku wondered if Shinsou was afraid of the water. He hadn’t chosen to join them as far as Izuku knew.“The old stories say that the watch goes first, and there’s time for the rest of the crew to tie themselves down if they’re not the first target. Who knows if it’s true, but it is one of the reasons that no one wants this job,” Izuku explained. He sighed and rolled his shoulders. It wasn’t a secret that night’s watch at high sea was the worst job on the ship, but he’d come to appreciate the solitude… And, more recently, the lack of it. “Why did Nemuri ask me to do it if she’s trying to keep me safe?” Shinsou questioned. Violet eyes narrowed, and his grip tightened around the ropes. Izuku could see how much he struggled. He had no idea what brought Shinsou aboard, but the other man clearly felt out of place. “She probably knows I’d go first,” Midoriya answered honestly. “I was thinking… Maybe she does trust me a little. Maybe I’m not just here because someone took pity on me,” Shinsou admitted. He released his hold on the rig and glanced up at Izuku.“Our Captain doesn’t pity as far as I can tell,” Izuku answered honestly. He offered Shinsou a genuine smile - an attempt to show him his appreciation for opening up. “She’d have told whoever asked to find a babysitter if she didn’t think you could earn your keep.”Shinsou seemed to relax. He leaned against the mast and turned to look out toward the water. Izuku felt a faint prickling at the back of his neck. Was it even possible to know that his Kacchan was looking for him? It felt like it was. A faint pull at his gut urged him toward the railing, but he knew better than to draw Kacchan from the water. Izuku braced himself against the mast. Katsuki was smart. If Izuku stayed away, he’d go. He could probably hear them talking anyway. “Hey… I’m sorry I was an ass,” Shinsou muttered. “I’m going through something, and I wasn’t ready to talk about it.” His voice was still monotone, but there was some change in it. Warmth bubbled in Izuku’s chest at the sound of it. He’d always been quick to forgive, and this was the first time he’d shared the ship with anyone close to his age. “I understand,” Izuku answered easily. He went back to checking each rope individually. All were in good shape, as they usually were.“You’re not going to ask me what it was?” Shinsou prompted. “No. I think you’ll tell me if you ever want to,” Izuku answered. He’d never met anyone who appreciated being pressed for information, and Shinsou had practically begged for space. The last thing Izuku wanted to do was pressure him. He could see Shinsou’s lips twitch upwards with the first smile Izuku had ever seen on his face, and, suddenly, Izuku felt a little less alone. The voyage was better with Shinsou’s company, but Izuku was disappointed that Katsuki wasn’t able to visit. It was probably for the best. Sliding into the water to finally touch the siren’s face was more enticing than ever.Would Kacchan indulge him before dragging him under the water? “Midoriya… What’s that in the water?” Shinsou questioned. His voice was unusually quiet and severe. Whatever it was, it frightened him.Izuku’s heart raced. It couldn’t be, right? Katsuki wouldn’t be so reckless, and this was further out than he usually was. Still, what else would be visible in the water in the middle of the night?“What did you see?” Izuku whispered. He approached Shinsou’s side silently and peered into the water. He didn’t see anything, but he knew better than to pretend it was nothing. “M-Maybe I just imagined it,” Shinsou muttered, but his eyes were wide and expression guarded. Izuku knew that look. He’d seen something. Shinsou wasn’t the type to jump at shadows. “We need to tie ourselves to the mast,” Izuku answered decisively. He made quick strides back to the mast to gather the leads. His eyes flickered to the bell near the cabin. Once they were secured, he’d ring it to alert the crew. Shinsou stepped away from the edge, but he looked perplexed. He opened his mouth to speak, but he was interrupted. The moment his lips parted, something… Strange began. It wasn’t quite music, but the moisture in the very air seemed to vibrate with the sound of it.
This. This must be siren song.
Izuku’s entire body shook. It was real. Real, genuine siren’s song. It was so similar to Katsuki’s way of communicating, but it was also different. The song conveyed meaning, but it was like a scene wrapping around his thoughts. More importantly, it was a lie. When Katsuki trilled for him, Izuku could hear his earnest meaning as clearly as any spoken sentence. This song spun a lie that seemed like the truth, but Izuku could feel that it wasn’t for him. The lure tugged at him like a physical force, but the lie it spun was something he’d never dream of.It promised care and acceptance and freedom from loss. Some of those things spoke to Izuku’s soul, but the lie it spun focused on dark, cozy warmth in a familiar space. He could see the flashes of faces and feel the echo of sensations that were completely unfamiliar to him. Each verse felt like the gentle caress of a trusted hand through his hair.
It must have been for Shinsou.
The other sailor’s shoulders drooped as ever-present tension left his body. He turned toward the sea. He didn’t fight it, or maybe he couldn’t as he made steady steps over the wet deck toward the railing. Izuku had never moved faster in his life. His heart pounded in his ears. His throat felt tight as he dragged the rope around Shinsou. The man struggled, but Izuku was stronger than he looked. He wrestled a thrashing Shinsou to the deck and wound the ropes. Practiced hands tied harsh knots to keep the sailor bound to the ship. Izuku felt a thrill of relief when Shinsou seemed to free himself from the siren’s call. Shinsou shook, his eyes widened, and he took several harsh breaths. Izuku’s entire body shook with him. Izuku’s clothes were soaked through, but he still scrambled to find his own ropes as quickly as he could.
It was too late. Of course, it was.
Izuku knew then that it wasn’t Kacchan lingering in that inky blackness. Kacchan, who never sang for him, could have drawn him in so easily, because Katsuki knew him. He could have spun a song that would have made Izuku beg to join him. When this song shifted, it wasn’t perfect, but it quickly grew in strength. Izuku could hear the rage in it even as it hooked him deep. False promises wove together until they hummed through Izuku’s very being. It offered all he’d lost; as though everything he’d ever known was lurking just beneath the surface. He could hear his mother’s laugh and feel his father’s fingers combing through his curls. His skin seemed to warm with artificial sunlight, and he could smell freshly cut grass. He knew it wasn’t true. He fought against it with all he had. But it didn’t seem to matter. It wasn’t Izuku’s mind that the siren sang too. Izuku could feel it pulling at the emptiness in his chest. His body moved on its own, as though physically dragged by the promise of being filled with warmth and happiness once again. Izuku only faintly registered the sounds of the ship’s bells behind him. At least Shinsou had been able to alert them. Someone’s hand brushed his shoulder, but it was too late. His body tipped over the side and into the water.
----- CHAPTER BREAK -----
The icy cold of the water hit Izuku’s body with a shock to every sense at once. The unknown siren’s thrall no longer held him, but it had already done its job. The water was too dark. Izuku panicked and struggled toward what little light there was. The moon was still bright enough to shine over the surface, but he didn’t suppose he would reach it. If the siren was anything like Kachaan, it would be huge and fast. Izuku couldn’t see its shape, but its movement stirred the water around him as it circled. Izuku still tried. He had to try. He wanted to live. A powerful current spun him to the side again. Then - pain. Searing, blinding pain as his shoulder was torn open. Izuku struggled, but he couldn’t right himself. Blood filled the water. Izuku could almost taste it on his lips even as his lungs burned.
This was it.
A tail brushed his legs, and Izuku's mouth parted against his will. Sea water burned his mouth and throat as golden eyes lit the water in front of him. With the new sliver of light, Izuku could see the rows of sharp teeth as they parted before him. He was terrified, but, even now, he wasn’t contemplating death. He was focused on the fact that he would never see Kacchan again; that he wouldn’t meet his end under his own siren’s elegant claws and fangs. Instead, this vicious, crooked beast was going to steal him away.But then, a scream shook the water. It was vicious and territorial. It hurt Izuku’s ears and left his vision blurry even beneath the waves, but Izuku would know its owner anywhere. The imprint of that voice had been carved into his every thought for months.Kacchan. A fast moving mass charged into the golden-eyed siren. The sudden pressure knocked Izuku to the side like a rag doll. He didn’t have the strength left to struggle as the two sirens tore into each other. New sounds filled the water, but Izuku couldn’t understand any of it beyond the apparent rage.He may have blacked out for a moment, but then there was a strong arm around his middle. Unknown fingers curled against his lower back, and pressure flattened Izuku’s hair as he was pulled upward. Izuku broke the surface with a gasp and a series of wet coughs. He was shaking violently as he looked in the direction of the ship. It had gotten so far. He could only tell where it was because of the false light on the horizon. “No, no, no… It can’t happen like this,” Katsuki clicked and warbled. “If I can get you to the ship, can you get up? Would your humans help you?”“N-No,” Izuku managed to answer through chattering teeth. “They won’t risk a siren attack… They’ll leave me.”He turned his face toward the siren and was struck by his savage beauty. Izuku’s fingers were already numb, but he reached up to stroke Katsuki’s cheek. The skin was smooth under his touch. Katsuki’s features were so much sharper than Izuku had realized. The fine line of his cheekbones were striking, and his eyes were unnaturally vibrant. It felt different to be pressed close to him. There had been too much distance between them before to see the faint flutter of Katsuki’s gills or to appreciate the fine texture of his hair. This close, Izuku could see the complex combination of reds that made Katsuki’s eyes shine with the depth of fine gemstones. Izuku had wanted to touch him so badly for so long. Katsuki pulled him closer, and Izuku rested his head hesitantly against Katsuki’s shoulder. He was still shaking, but it still felt right. He wished he could enjoy it more, but his mind raced even as his body started shutting down. One thing was clear, even to Izuku’s frazzled mind - Kacchan had protected him. It was only the siren’s muscular arms and swaying tail that kept Izuku’s head above water. He hadn’t been eaten yet, and Katsuki’s clawed fingers were examining him without harm.Why was Izuku still alive? Katsuki had been waiting all this time to get Izuku into the water, and yet…“It wasn’t supposed to happen this way,” Katsuki whispered. The siren rested his forehead tenderly against Izuku’s, and the human praised what little life he had left that he could feel the gentle pressure. The position was intimate. No human had ever held Izuku like this. He couldn’t find it in him to be scared despite the constant moving of the powerful, spined tail swaying in the dark water beneath them. “Isn’t this what you wanted?” Izuku muttered. His voice sounded slurred even to his own ears. His numb fingers attempted to make their way up into Katsuki’s hair. He’d always wonder how it managed to hold that beautiful shape even in the water. Now he might never know, but he could at least feel it.“You didn’t sing for me. It was someone else,” Izuku continued. He wished he didn’t sound so betrayed. Had he really wanted Katsuki to sing for him?“It had to be your choice,” Katsuki attempted to explain. His voice was mournful and soft. It was a caress on Izuku’s aching brain, and Izuku wanted to hear so much more.“It’s not too late,” Katsuki continued, but it sounded like denial. “Choose me, Izuku.”“I’m already dying, Kacchan,” Izuku reasoned. The barest hint of a smile spread over Izuku’s trembling lips. “You have me.” “I’m not just asking for your flesh, Deku. I’m asking for your life,” Katsuki pressed. Luminous, red eyes stared deep into Izuku’s. “You have to choose me. Over everything else. Offer me all that you are and mean it.” “There isn’t another choice,” Izuku argued. His smile broke with a quiet sob that shook his body. He wasn’t ready to go. He’d only just gotten here. He was only just now touching his Kacchan for the first time. It wasn’t fair. Nothing ever seemed to be.“Please,” Kacchan crooned. He nuzzled the side of Izuku’s head gently, and Izuku leaned into his touch. He was trying to focus, but it was so difficult.“Will it hurt?” Izuku asked.“Yes, but I’ll be as gentle as I can,” Katsuki promised. The tips of clawed fingers brushed wet curls from Izuku’s face. Their noses touched as the siren looked deep into Izuku’s eyes. Katsuki’s gaze was so expressive, inhuman; perfect.
It was always going to end like this wasn’t it?
The dark truth of it rattled Izuku to his core. He didn’t even care how Katsuki chose to take him. “You have to say the words, Izuku,” Katsuki prompted. The sweet sound of his chittering darkened with a sense of urgency. The arm around Izuku’s back tightened. Was hard pressure all he could feel anymore? “W-What words?” Izuku slurred. His voice sounded odd to his own ears. Were his teeth still chattering? Izuku couldn’t even tell past the growing numbness.“Katsuki, I offer you my life,” Katsuki pressed. The meaning was measured and clear despite Izuku’s muddled thoughts. Izuku’s eyes followed those perfect lips like they were the most important thing in the world, and maybe they were. Not even the flash of lethal fangs could move Izuku to fear his Kacchan.“K-Katsuki… I, Izuku M-Midoriya, offer you my life,” Izuku offered, and he meant it. He wondered if Katsuki could hear his sincerity the way Izuku could hear his. A great thrumming started in Katsuki’s throat. Izuku could swear the water around him vibrated with the strength of it. Izuku’s head went even fuzzier as the soothing thrum seemed to conflict with the bitter cold.One moment, Izuku was still staring into crimson eyes, and, the next, he was pressed down into the depths of the sea. Izuku hadn’t even had time to take a breath, but what did that matter? He could only barely see Katsuki’s outline against the moonlight above them. He was so fast - a breathtaking, lethal predator. What Izuku wouldn’t give to see his Kacchan in his element during the full light of day. The hum rose until it became a full song. It wove itself like a lullaby, but Izuku didn’t have time to enjoy it. Katsuki struck with unbelievable speed. Razor, sharp teeth sank deep into Izuku’s shoulder, and heat burst through the fresh wound. Izuku opened his mouth to scream and lost what little air he had left. Blood filled the water again. The tendrils rising from his shoulder were thick enough to blot out the moonlight. Katsuki’s teeth must have left him, because the siren struck again. They lodged into the junction of Izuku’s neck and shoulder on the opposite side. This time, Izuku inhaled salt water with his cry of pain. It stung his lungs viciously. He thrashed. It hurt. Everything hurt. Surely, it was almost over. But then Katsuki’s hands were on his cheeks again. In this cold, even the siren’s fingers felt warm on Izuku’s skin. The human cracked his eyes open to stare into luminous, crimson eyes.They took up all his vision. They were so beautiful - so terrible - so perfect. Then the siren’s lips were finally on his for the first time. Izuku’s body jerked once in shock, and then the siren breathed something into him. Fire burned through Izuku’s brain. His vision whited out as pain and heat wiped away everything he had ever been.Finally, finally - Izuku let go and closed his eyes on his human life forever. Katsuki swam toward his den at top speed. His hand rested firmly against the back of Deku’s head to keep the human’s face tucked safely against his chest. His claws were finally laced in those gorgeous, green curls, and he couldn’t even celebrate it. They were further from safety than Katsuki was comfortable with, and his mate had been attacked by one rogue already. He didn’t want to acknowledge the way his fingers shook.Izuku’s shoulders were still bleeding. Katsuki hoped that was a good sign. If nothing else, the scent of blood and blind aggression would keep the members of his tribe away from his den for a while. Let them think he’d finally killed his human; that he’d dragged his prize down to feast upon. Katsuki pulled Izuku closer and nuzzled his unusual, cloudy hair. The strands were so soft and tickled his nose whenever he pressed close. The young alpha’s instincts were a mess. Every inch of him screamed that his mate was vulnerable; his newly bonded mate. Katsuki was sure that the empty pit opening in his chest was the bond taking root. He couldn’t feel Izuku yet. At least, not in the way one should feel their mate, but he was still certain it had worked.If the bond had taken, and Katsuki, himself, was still alive; then Izuku had to be alive too. Katsuki needed it to work. He felt the pull to Izuku from the very beginning. No matter what anyone thought or suspected, Izuku was going to be his mate or Katsuki was going to lie down and die with him on the ocean floor.It wasn’t a matter of being stubborn. It was a deep, primal truth that Katsuki had no desire to fight. Izuku was his, and Katsuki had waited a long time to solidify that truth. Deep-seated relief stole all of Katsuki’s tension once he finally approached his den. It was a spacious cavern situated cliff side and surrounded by thick sea grasses and coral. Katsuki had been working on it since the moment he met Izuku all those months ago.It was further from the tribe than most would choose to live, but he’d known he would need the separation while Izuku underwent the change. The siren dipped inside and made his way to the very back of the den. He settled Izuku in the softest patch of sand, then hurried back to check the entrance. Katsuki hovered there for several minutes to make sure no one was foolish enough to follow him. Then he eagerly returned to examine his human.
He’d waited so long to touch him.
He reached out with uncharacteristically gentle hands to survey the damage. It was so surreal - to finally be touching the object of his obsession. He turned Izuku’s face from side to side and examined his features in awed silence. Izuku’s body hadn’t broken the way some land creatures did when they were dragged to deeper water. His eyes were still in his skull, at least. He was colder now than he had been, and his heart refused to beat. But he didn’t float either. Clawed fingers absently played with the odd, rounded appendages of his human’s hands. Human bodies were so odd. They were gawky and had no sense of fluidity. As powerful as their legs seemed, they had no sense of movement. Every bit of them was rounded and blunt instead of sharp and dangerous. Still, Katsuki found his mate beautiful. He’d have loved Izuku no matter how he found him. Katsuki wasn’t sure what to do now. He couldn’t be entirely sure that the transformation was even possible. He brushed his fingers slowly through silken hair again. His tribe had never known a human turned siren, but the stories were clear.Most of his tribe agreed that it must be possible, but they also found it abominable. Still, Katsuki had to try. Izuku was his, and he’d kill anyone who got in his way. No. Their way. Izuku wanted him back. This wasn’t supposed to be possible if Izuku didn’t want him back. A bond had to be welcomed to form. The siren rumbled low with affection, but his eyes flickered to the entrance of his cavern to make sure that no one nearby could hear. Katsuki had never purred for anyone else, and no one needed to know how gone he was already.Not that they’d be surprised. Everyone knew that he was lovesick. They’d all guessed what he was up to long ago. Katsuki coiled his body carefully over Izuku, as though to shield him from the world. The siren knew damn well that his mother would come by to check on them eventually. He only hoped the transformation would be obvious by then, because Katsuki would have to kill her if she tried to hurt his mate. The siren settled in and kept his eyes trained on the entrance. He wasn’t sure how long he waited before he gained the courage to check Izuku over again. His human was eerily silent and still. Izuku looked… Exactly the same. Katsuki's stomach lurched as he drew his knuckles gently down the length of Izuku’s body. Deadly claws tucked into his palms to avoid harming the delicate, human skin.Bravely, he brushed the sensitive pad of one finger over Izuku’s pale skin. It felt waxy beneath his fingers, and Katsuki bit into his lower lip until he tasted blood. It was a bad sign; too corpse-like to indicate a transformation. He fought against the despair that began to bloom in his stomach. Nothing was final yet. He prodded gently at Izuku’s clothes and was surprised to find that some kind of crust had gathered in the wrinkles. Under closer inspection, the crust looked like a gathering of little, salt crystals. It was odd. There was no reason that anything should be crystalizing here. It had only been a few hours since they’d arrived. That told Katsuki that they were forming quickly. The siren allowed himself some tentative hope. His body began to rumble softly over Izuku again. Somehow, he hoped the soothing croon would coax his mate back to life. The crystal spread rapidly over the next few hours, or perhaps days. Katsuki was too enraptured with its progress to even hunt at his den’s entrance. He couldn’t bring himself to leave his mate’s side for even a moment. Instead, he watched Izuku’s face with growing fascination. He memorized Izuku’s every pale feature - counted eyelashes and freckles, marveled at the shape of his lips, and appreciated the wispy curl of his hair. Before long, the crystalline shell was covering those features one by one. The crystals started thin, but they thickened with time and hardened into a protective shell.Yes. He was sure of it now. This was the start of the transformation. Almost the moment the crystal chamber sealed, Katsuki began to feel the stirrings of the mate bond in his chest. He rested his palms protectively over the shell, and he was certain he felt movement just beyond the film.
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Katsuki was beginning to waste. He’d gone too many days without feeding, but he was afraid to leave Deku’s side. He knew it wouldn’t be long before someone came looking for him, and he couldn’t risk anyone approaching Izuku while he was unprotected. The merman circled the short span of his den over and over. He was agitated and worried. Knowing that something was happening beyond the crystal wasn’t enough to calm him. He had too much to lose.He stiffened with the first stirring at the edge of his den. He crowded the entrance and fanned his fins in a threatening display. He was the most terrifying of their tribe. It was an undisputed fact. Katsuki was the ideal alpha male among them with the bright streaks of red orange along his length; large size; deadly spines; and dense muscle. No one approached his den without permission. “Katsuki,” an unimpressed voice hissed from the entrance. Katsuki hastened to correct himself - no one but his mother. Their tribe was led by a council of veteran fighters, but Mitsuki sat at its head. An impressive lineage had fast tracked them both to seats on the council, but Katsuki had never coveted the tribe’s approval the way his mother did. He kept his standing with sheer force and intimidation. Katsuki didn’t move when Mitsuki slipped past the cave entrance. He did his best to cover Izuku completely from her vision, but his scent lingered in the cavern. The scent of blood didn’t, and he was sure Mitsuki was already connecting the dots. Katsuki was loath to admit it, but he'd inherited his sharp wit from her.“Hoarding a corpse won’t change what you’ve done, Katsuki,” Mitsuki admonished. “I know you had a fascination, but it’s over now. You’ll do away with it yourself now, or I’ll have the men drag that filth out by force.”Katsuki’s sharp hiss of warning made whatever mer lingered outside flinch away. Katsuki swam back and poised himself over the crystal with obvious intention to strike. He’d die before he let anything happen to his mate. He’d kill whoever he had to. “It’s not a corpse,” Katsuki snarled. His voice was garbled and shrill with the strength of his rage. Anxiety sent adrenaline coursing through him as he waited to see what his mother would do. “We’re bonded.”Katsuki’s posturing hadn’t put Mitsuki on her guard, but the word ‘bonded’ did. The shrill screech she released had Katsuki scrambling to better cover his mate, but she didn’t charge. Instead, her men entered. She was playing dirty this time. The men she’d ordered along were some of Katsuki’s very few friends. Eijiro entered first and Tetsutetsu behind him. Katsuki’s tail thumped the cavern in warning, but Tetsu didn’t hesitate and Eijiro was always right behind him. For once, Katsuki showed them no mercy. Even as weak as he was after days without proper feeding or rest, it took reinforcements to drag Katsuki from the cave, and he never stopped trying to drag himself back. He screamed like a banshee all the way to the cells. He let the sound of it fill the entire area along with the thick blood spread by his violent struggle. All four of the mer who dragged him away would bear the scars forever. Even Eijiro, with scales as hard as black stone, had been pierced by Katsuki’s vicious teeth and claws. Katsuki wasn’t unscathed. His nail beds were brutally bloody and torn. He was missing teeth. While those would grow back, the gashes on his side and neck would certainly scar.The worst of it was the dark hole in his chest that grew more and more painful as he drew further away. He could scarcely breathe by the time he’d locked him in one of the tribe’s few cells. Katsuki couldn’t rest. He beat himself bloody against the cavern walls, and, for the first time in his life, he begged. His pride already hurt. He’d never imagined he could be dragged away from Izuku, and so he begged like a child to be let out. His mate needed him. He had to get out of there and back to Izuku before his mother killed them both. When Izuku woke it was in complete darkness. His chest tightened with panic. It was every sailor’s worst nightmare to wake in the endless blackness of the sea. He was disoriented and confused, and the throbbing at the base of his skull told him that something was very, very wrong.
He wanted Kacchan.
He opened his mouth to call for him, but all that came out was a wheezing cry. Something wasn’t right. This wasn’t breathing. Wasn’t talking. Blood filled his mouth with the painful movements, but the next time he made a noise, he understood it. “Kacchan,” Izuku wheezed. “Kacchan?!” An incredulous voice hissed in the dark. It wasn’t Kacchan. Izuku wanted to recoil, but no part of his body would respond.
He couldn’t feel anything…? Why couldn’t he feel anything? Was he dead?
His next sound was little more than a sob, but whoever was with him wasn’t paying much mind. “My Katsuki must like you very much to let you call him that. Tell me, did he sing you off the ship?” The voice questioned. A hand absently brushed Izuku’s forehead, and he felt something like nausea building at the casual caress. “What did he tell you? What did you do?” The voice pressed. “I-I gave him my life,” Izuku croaked. The sounds he made were not as pretty as Kacchan’s, but he could understand himself. “It hurts… It’s like I can feel him in my…”Izuku tried to sit up, but the pain that came with trying to move had him screaming. The sound echoed painfully in their small space, but it was nothing like the growing panic in his chest. Now that he’d said it, the emotion was overwhelming.
Where was Katsuki?
Izuku could feel him. It was like he’d been just beyond his reach, and now the man’s every thought and feeling were pouring into him at once. There was a great flashing behind Izuku’s eyelids and growing pressure in his temples. “Where?” Izuku hissed. “Where is Katsuki?” “My foolish, idiot son.” Katsuki’s mother, then? She sounded furious. “It is unusual for a bond to form if both parties haven’t exchanged bites… I guess you really did offer your life, didn’t you? A bond requires mutual desire and surrender to form.”When the woman spoke next, it wasn’t to address Izuku. She spoke to someone nearby. “Go release my brat. He’s probably even angrier with the mate withdrawals.” There was a rush of water around them, but Izuku couldn’t tell if that meant they were now alone. The complete darkness before wide, open eyes was surreal.“What did he tell you about the tribe?” The voice was closer now. It wasn’t quite a whisper, but he could tell she wanted the details without allowing anyone to overhear. Izuku’s aching brain raced. He felt dizzy despite his lack of vision. Was this why Katsuki had never spoken of other sirens? Was he not allowed? There must be rules. That was why the siren had never sung for him.“Nothing,” Izuku managed to croak. He tried to push the truth into the sound. It must have been enough, because Katsuki’s mother quickly switched gears. Her voice grew louder, as though to ensure someone else could hear her this time.Izuku’s heart raced. There was a power struggle here he didn’t understand. This was Katsuki’s mother. He had to hope she was keeping him safe, but he didn’t know how to help. Where was Katsuki? Was he in trouble? Hurt? “He’s foolish. Stubborn… I cannot imagine anything more foolhardy than to bond with a human.” The woman spat her words in disgust, but Izuku could hear the underlying tone of worry. Was bonding with Izuku dangerous for Katsuki?“W-Why…?” Izuku asked. His teeth chattered. They felt strange, like they were rattling in his head when his mouth moved, but they were also one of the few pieces of him that didn’t hurt. “You have to be careful, Iz-u-ku. A bond can double a siren’s life, but only if you both survive long enough to enjoy it. You live or die together now, and my son, the strongest of us all, has bound his life to a weak, defenseless human.”There was a short pause while the woman considered her words. “It will be a miracle if you both survive the change. Impossible that you live long enough to make me think this wasn’t a fatal mistake for my only child.” The anger began to leach from her tone, and Izuku could hear the notes of mourning growing stronger as she continued. “Every year there are less of us. We grow weaker. Fewer children are born. Our tribe is in peril, and yet my heir does this.”Izuku didn’t know what to say to that. He had so many questions but no real strength to pull his thoughts together. He had no idea how to comfort or soothe in this new, unfamiliar place. Fortunately, he didn’t have to. Izuku felt desperation and affection bloom in his chest. The feelings weren’t his until suddenly they were. He wasn’t sure how he knew, but, even in the dark, he felt Katsuki arrive. A painful thrumming started at the back of his throat and some of his panic eased.“You broke the chamber!” Katsuki seethed. His hisses were shrill with blind rage. “You could have killed him!” “We had to speak to him. It’s tribal law. The damage is minimal, and he’s talking. I guess that means it’s working, and that you didn’t soil your den with some rotting, human corpse,” Mitsuki rushed to argue. Her words matched Katsuki’s heat and intensity, but Izuku could hear that she was drawing further away. “Out! You and all of your men. Stay OUT or there will be blood!” Katsuki snarled. He was moving further away as well - herding his house ‘guests’ out of his space.“Are you challenging me, Katsuki?” His mother hissed. “Do you want me too?” Katsuki growled. His voice was pitched so low and dangerous that Izuku shuddered despite the painful throbbing. Still, his mother must have decided not to press, because a fresh current told Izuku that the other sirens were leaving. Katsuki continued to snarl and churn the water in their home with angry pacing until the other mer were long gone. It was only then that he returned to Izuku’s side. Izuku tried to sooth him in some way. He could taste the blood in the water, and he could feel the hurt through the connection in his chest that could only be their bond. “If the crystal reforms, you must not fight it,” Katsuki ordered. His voice had gone soft with deep affection. Izuku closed his eyes and focused on the soothing timbre while he tried to form his next question.“Kacchan… What’s happening to me?” Izuku could hear the fear in his own voice. He wished he could have hid it, but he was too tired and numb to even attempt to figure out how this new form of communication worked. “You offered me your life, and I gave you a new one,” Katsuki answered.He said it so easily, as though it hadn’t changed their lives forever. Affection warmed the words, but Izuku could hear an underlying apology. So much had been kept from him. Izuku couldn’t possibly have known what to expect, and he was overwhelmed with the sudden changes.“I can’t feel anything,” Izuku stated. His lower lip quivered. He knew he’d be crying if he wasn’t somehow underwater. His chest tightened in a way that he definitely could feel. He was beginning to panic. He took a few deep inhales in an attempt to stave off an attack. And then Katsuki started rumbling for him. The sound was low and sweet, and Izuku felt affection and reassurance thrum through the tightness in his chest and throat. Izuku’s body began to relax, and blissful numbness crept up his limbs to take the pain away once more. “You’re still changing, Izuku. You have to rest… But you’ll belong to the sea when you wake,” Katsuki promised. It sounded foreign to Izuku. Being dragged to the bottom of the sea was strange enough, but Katsuki’s affection was blowing his mind. His Kacchan didn't rumble or offer reassurance. He postured and hissed and threatened violence until he got his way. But this felt different. Izuku could feel the way Katsuki’s bulk settled protectively over him. His thoughts quieted and his body relaxed under Katsuki’s care. Something in him trusted Katsuki with everything - something deeper and truer than Izuku could explain even by instinct. “You are my mate now, Izuku,” Katsuki explained. Careful claws made their way into Izuku’s hair and began stroking through green curls. “I will keep you safe. You only have to rest.” The thrumming continued, and Izuku let his eyes flutter shut. He wanted to fixate on the word “mate.” He wanted to understand, but he didn’t have to - not yet. He had nothing to fear, because Katsuki was here. The realization crashed over him all at once. Katsuki cared. If what his mother said was true, then it was even more than that. Did Katsuki love him? He’d done all of this to bring Izuku into his world; not to eat him. All of those months of getting to know one another, all of those words of comfort, and every offer Katsuki had made. None of it was untrue. It had all been to bring him here; into Katsuki’s world. An unfamiliar sound rose at the back of Izuku’s throat. Sightless eyes opened once more as he recognized the affectional trill for what it was. He’d heard Katsuki make it a thousand times, just before he asked Izuku to join him.
He was becoming a siren.
Katsuki’s rumble deepened with pleasure. The siren shifted, and Izuku could feel Katsuki’s nose and lips curiously exploring his face and hair. Izuku was shocked when an unusually long tongue slid over his face and through the winding locks of his hair.Katsuki was grooming him, and Izuku was enjoying it. His aching thoughts fell away in favor of a soft rumbling of his own. Izuku was exhausted, and it was impossible to keep his eyes open while his mate was being so unnaturally soothing.
----- CHAPTER BREAK -----
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When Izuku woke again, his vision was beginning to clear. It was dim, but he could make shapes out again. His body was still numb, and what little he could feel hurt. He must have made a soft noise of complaint, because a moment later there was a hand brushing through his hair. “Kacchan,” Izuku greeted. He allowed his eyes to flutter closed for a moment while Katsuki’s claws drew patterns on his scalp. “You’re awake?” Katsuki rumbled back. Izuku exhaled with a soft hum in response, and Katsuki’s muscular body shifted in the water above him as the alpha settled closer. His proximity seemed to ease the pain until it was only a dull ache. “The crystals around your face have begun to shed,” Katsuki explained. Izuku could hear the smile in his voice, but he had no idea what he was talking about. “Crystals?” Izuku prompted. “You’re encased in crystalline stone. The sea chose to shield you for your transformation. My mother broke the area around your face, but the change has continued,” Katsuki explained eagerly. His hand drew downward until it cupped Izuku’s cheek. “The crystals are weakening, but you’re not quite ready yet.”Izuku’s mind raced as he absorbed the new information. He wished he could turn his body and take a look around. He still couldn’t move, but the implications blew his mind. Encased in sea crystals? An ocean chrysalis? Who knew such magic still existed in the world?“Your muttering is cute,” Katsuki rumbled.Izuku’s mouth closed with an audible click. That felt different. Experimentally, he brushed his tongue over his teeth. The movement didn’t feel the same. Something had definitely changed around his tongue, but it was the teeth that allowed him to really feel the difference. They were sharp, and his gums were tender. It was possible that his fangs were still growing in, but he was no longer defenseless. The change should have unsettled him. Instead, Izuku felt a thrill of excitement. This was happening. This was real. “Do you think you could eat for me, beautiful?” Katsuki pressed. His thumb swept over Izuku’s cheek, and the fledgling siren opened his eyes to blink slowly at his mate. Katsuki’s smile widened. The alpha had been watching Izuku closely since his mother left, but this was the first time since then that he’d been able to look into Izuku’s eyes. They were still wide and green, a color that was never seen in Katsuki’s pod, and now the power of the ocean glowed within them. “Eat?” Izuku questioned. The thought hadn’t even occurred to him, but the idea of food started a whole new ache in his changing body.“My instincts say I should feed you,” Katsuki answered, but his tone went dark, implying that his instincts were actually screaming at him. “But I know you’re still changing.”“I’m starving,” Izuku admitted. He tried to tilt his face to get a better look at his mate. The darkness seemed to lift when his eyes met Katsuki’s. His heart stuttered. The siren looked different under water. He belonged. His stubborn hair was still shaped into spikes that moved gently with the current. Brilliant fins swayed to the same rhythm, and his scales seemed to shimmer with every subtle shift of his serpentine body.Izuku only wished the next thing he saw wasn’t Katsuki tearing the belly out of a dead fish. The siren chewed what was in his mouth. Izuku felt sick, but it was even worse when Katsuki pulled the fish pulp from his mouth and brought it to Izuku’s lips. The former human’s stomach revolted. He turned his face away, and Katsuki made a soft sound of concern.“Deku… You have to eat,” Katsuki clicked. He continued to hold the fish pulp nearby, but Izuku couldn’t even look at it. Even the glimpse of white, fleshy ribbons between Katsuki’s fingers had been too much for him.“Humans don’t eat raw fish,” Izuku protested weakly.“Sirens do… And you have to adjust,” Katsuki reasoned. The rumbling began again, and Izuku’s heartbeat slowed with the low and soothing sound of it. His mate leaned in and nuzzled Izuku’s curls, and his face drew downward until he could rub their cheeks together.It was hard to look away or keep his tension when his giant, predatory protector was cuddling him like this. Glowing, green eyes narrowed, and his lips pulled into a pout.“Please?” Katsuki crooned.Izuku looked doubtfully at the fish paste in Katsuki’s hand. He took a few deep breaths and tried to prepare himself to try it. His face scrunched up and his mouth felt strange. He must have looked truly disgusted, because Katsuki began to laugh. “You can eat by yourself when your fangs finish coming in,” Katsuki promised.“It’s gross, Kacchan,” Deku argued. “What if I fed you directly?” Katsuki offered. His rumble deepened, and Izuku could hear the suggestion in it. Izuku’s brow only scrunched further while he thought about what ‘directly’ might mean. Katsuki let the fish guts in his fingers float away, and Izuku watched with rapt attention as Katsuki scraped the other side of the fish and lifted the remaining flesh. His mate chewed for a moment, and then leaned forward.Izuku would have squirmed away in sheer embarrassment if he could. Rationally, he knew this wouldn’t be their first kiss, but it would be the second. He really would have preferred that fish wasn’t involved.Katsuki’s mouth found his, and his lips were so soft. It didn’t make any sense for them to be so soft and gentle when sharp teeth rested just behind them. The insistent press of them somehow made the fish taste sweet as it passed over Izuku’s tongue. The texture was unfamiliar and strange, but it wasn’t as gross as he’d expected.Katsuki’s tongue stroked his own for a moment, and Izuku swallowed obediently under the attention. It wasn’t bad, and the fish was pushing the numb feeling out of his belly.“More?” Katsuki offered. Brilliant, red eyes were narrowed with affection as he waited for his mate to accept his help.“Yeah,” Izuku answered.Katsuki fed him several more fish, and, soon, Izuku was feeling relaxed and warm for the first time since he’d awoken on the ocean floor.
After a few more days of tender care, the crystals began to weaken and fall away. Izuku peeled himself from the stone little by little, and Katsuki was by his side the entire time. The siren groomed him meticulously as his scales were revealed one by one.Izuku’s new body wasn’t what he expected. Instead of dark, colorful scales like Katsuki, Izuku had a milky white tail tinted with sickly gray. His fins and talons were the same. The color was concerning. It was too similar to fish meat or sickness, but Katsuki didn’t seem concerned. The other siren swept his fingers slowly over the scales to ensure they remained smooth. “A little soft, but not unlike a newborn siren. They may harden with time. If not, we’ll adjust,” Katsuki promised. He shifted his body closer and snuggled in so that Izuku could share in his warmth. “Your mother was right, wasn’t she? I’ll be a weakness for you,” Izuku muttered. He looked down at his dull scales and swallowed against the tightness in his throat. Katsuki refused to say so, but Izuku knew he was worried. He had to be.“Deku…” Katsuki began. A hand found Izuku’s jaw and lifted his face until they were staring deep into each other’s eyes. Then he leaned forward and brushed their mouths together in a soft kiss. Izuku allowed his mate to guide him back against the sandy floor of their den while his mate kissed his worries away. Laying under Katsuki with the soft grains of sand caressing his new scales made him feel safe - protected from new, harsh realities. “We’re going to be okay. You’re my reason for living, Izuku. Maybe it is a weakness, but no more than my heart, my gut, or anything else I need to live are weak points,” Katsuki attempted to explain. The alpha’s eyes were narrowed as he watched Izuku’s face. It warmed something in the new siren. He trilled softly for his mate and leaned forward to brush their cheeks together. Katsuki pressed into the contact and released a few trilling clicks of approval. The sounds echoed off the walls of their den, and somehow that made this new place feel even more like home.“You said… I look like a newborn?” Izuku questioned. “Our children are born milky white and small and soft. They come into their colors as they age,” Katsuki explained. “For all we know, this is just the start of your transformation. But… This may also be a consequence of my mother’s interference.”“I’m sorry, Katsuki,” Izuku muttered against the siren’s lips. He didn’t know why he was sorry - for being soft, for his mother’s interference, or for the stress of his transformation. Izuku couldn’t help but wish this could have been easier for his mate. “Why? I’m the luckiest creature in this ocean,” Katsuki rumbled for him. Their lips were close enough that Izuku felt the way he smirked, and he could hear the smug satisfaction in his voice.Izuku’s eyelashes fluttered as he leaned forward to brush his lips over his partner’s. Katsuki believed what he was saying. Izuku could hear it. They were in this together.Inspired, Izuku swept his tongue into Katsuki’s mouth. At least that muscle had toughened up considerably. The other siren’s teeth didn’t cut him as Katsuki invited him in. Warm hands squeezed Izuku’s hips as Katsuki drew him closer. Their fins brushed sweetly as they wrapped around each other. A tingling sensation began building along Izuku’s spin as his new body reacted to his mate’s touch.The hand on Izuku’s hip traveled inward until a warm palm rested flat against Izuku’s belly and moved downward to the junction of Izuku’s torso and tail. Clever fingers pressed and explored. “Omega. That will make things easier,” Katsuki crooned.“Omega?” Izuku questioned. He began carefully brushing his fingers over Katsuki’s collarbones and shoulders. His fingertips were still sensitive enough to feel the fine texture under his touch, and he wasn’t sure he’d ever get tired of examining his new mate’s body. Katsuki’s musculature alone would have been enough to keep Izuku’s attention forever, but the man was also covered in lethal spines and shimmering fins. Izuku wanted to catalog every inch of him, and they’d have plenty of time, as long as Izuku managed to keep breathing.“Humans do not have omega? It means you’ll produce eggs for us,” Katsuki explained with a few curious clicks. “E-Eggs? You think I’ll produce eggs?” Izuku asked. He blinked dumbly at his mate as he settled more comfortably in the sand. “Does that mean…? Would they be… Viable?”“Of course they would be!” Katsuki growled. His eyes narrowed viciously, and Izuku could hear the implication. He worried that Izuku thought he was too sickly or wrong to have children, and that might be a concern too, but Izuku was more focused on the idea that it was even possible. “I mean that humans are usually born with either a penis or a vagina. They’ve divided by their organs. I-I was born without a womb, so getting pregnant wasn’t an option,” Izuku tried to explain.“That’s so impractical,” Katsuki huffed. His hands prodded Izuku’s abdomen again. He leaned a little closer and sniffed around Izuku’s gills, and then the alpha took Izuku’s hand and placed it beside his so that Izuku could feel what he did. “This pouch here is your womb. It only sticks out this way and feels soft here when the womb is developed and active,” Katsuki explained. “Your scent is also tinged with an omegan scent. Gender is subjective and subtle for sirens, so it’s difficult to pick up with scent alone.”“Subjective and… Subtle? How many genders do sirens have?” Izuku muttered.“Three primarily, although there are nuances between. Siren can be alpha, beta, or omega, but we are not born anything. We can transition when it suits us, though it takes time,” Katsuki explained. “Most siren choose to be beta. Their sexual organs are inactive, they struggle to put on muscle mass, but they also expend less energy. It’s easier to survive.”“Alpha, like myself, can fertilize eggs. Omega produce eggs. Alpha and omega can develop more physical power, but they’ll waste away much faster than a beta if they’re struggling to stay fed.”“I have always been an alpha,” Katsuki finished. “If we decide to have children together, being an omega will make it easier.” “You think we could have…?” Izuku muttered almost to himself. He’d never even imagined that parenthood was an option for him. Izuku loved children, and he’d always been lonely. Sometimes daydreaming about having a family, however impossible it seemed, had brought him comfort. “We can try,” Katsuki answered with a grin; flashing all of his teeth. “It won’t be easy. There hasn’t been a pup in my clan for nearly twelve years, but I’ll do everything I can to put one in you.”“Over and over…” Katsuki promised with a low rumble. His thick, muscular tail rubbed slowly over Izuku’s, and the new siren whimpered as something hot slid over his pale scales. Izuku took a deep breath to steady himself before finally glancing down at Katsuki’s dick.He didn’t know what he expected, but it wasn’t at all human. The shining scales of Katsuki’s pelvis had parted to reveal a long, tapered appendage with a thick swell at the base. There were membranes along the sides that looked almost like frills. The rest of his length was textured with swells and divots, but the flesh itself looked smooth. The color was a sweet gradient of dark reds and oranges that complemented Katsuki’s scales. Something more viscous than water beaded at the tip. And it spread, shining and slick, over Katsuki’s length as he reached down to stroke himself. When the alpha’s hand reached the knotted base, Izuku could see movement. Just above the knot, there was a ring of soft, pulsing nubs that fluttered and brushed Katsuki’s palm. If those could move to invite touch, Izuku wondered how the rest of Katsuki’s shaft would react to his inner walls. The omega flushed darkly. He glanced up at his mate, and found hooded eyes watching him fondly.“We don’t need eggs to have sex… Mate,” Katsuki rumbled. His tail curled against Izuku’s, and the gentle pressure sent heat racing south. “You’re going to teach me how to have sex before we even swim?” Izuku teased even as his arms curled around his mate’s neck. Delicate claws combed through Katsuki’s hair as Izuku brushed their noses together.The prospect should have been terrifying. Izuku had never had sex as a human. He couldn’t imagine how the siren’s dick was ever going to fit inside him, but he trusted Katsuki. Moreover, Izuku wanted him.Arousal already made his blood feel hot and his stomach tight. “Fuck yes,” Katsuki answered eagerly. Deadly fangs began tenderly nibbling Izuku’s neck as he rocked Izuku down into the sand. The alpha’s tail curled tighter and shifted over Izuku’s scales. Alphas must run hotter, because he felt so warm. Izuku could feel every brush of heat along his new scales. They were much more sensitive to touch than he’d expected, and it set his body tingling and trembling. Suddenly very curious, Izuku reached down and brushed just the tip of his finger against his new slit. He hadn’t had the chance to explore it yet, but the scales around the opening were even more sensitive. They were flushed just slightly pink, as though teasing the existence of the soft passage beyond.It was on the tip of Izuku’s tongue to ask about preparation, but maybe he didn’t need it now? Katsuki had said he was an omega. This new body was made to take his mate, and he was already hot with lust. Surely the claws wouldn’t feel good on his soft, inner walls either. His pulse must be racing or perhaps his nerves were leaking into the bond, because the alpha lifted his head to get a better look at Izuku’s face. “Calm down, Izuku,” Katsuki ordered. His pupils were dilating with the strength of his arousal, but his brow was also furrowed with concern as he nuzzled against Izuku’s jaw. “Are you alright?” “It’s not that… I-I just don’t know how. This body is new to me,” Izuku muttered nervously. He wasn’t even sure how to control the muscles that Katsuki was constricting with his tail. Katsuki knew just what he was doing. At least Izuku had to assume he did, because the omega’s body was already on fire. Izuku wanted to be good to him in return, but he wouldn’t have known what to do even if he’d still had legs to wrap around Katsuki’s hips. “Then we’ll learn it together,” Katsuki soothed. His chittering held an underlying promise that they didn’t have to continue. The alpha wanted the assurance of Izuku’s comfort. Izuku chittered back and nuzzled the side of Katsuki’s neck. The alpha’s gills tickled his face as they filtered water, and Izuku smiled into them. “We’ll start slow,” Katsuki promised. Perhaps Izuku had been too worried about claws, because Katsuki was careful and deft as his hand slid between their bodies to trace Izuku’s slit. The area was swollen and Izuku’s entire body twitched with sensitivity even at the explorative touch. The alpha crooned his praise into Izuku’s ear while the omega shuddered and did his best not to arch upward into Katsuki’s attention. He didn’t want to hurt his new scales by squirming too much under his mate’s sharper body.“Don’t worry, Deku.” Katsuki’s body rose in elegant coils as he slid himself down Izuku’s body. Their fins brushed sweetly as the alpha settled his face just above Izuku’s aching entrance. Izuku didn’t have as much feeling in his fins, but there was enough sensitivity there to tickle his senses. Izuku was confused as the alpha nosed around the junction of skin and scales. He wasn’t sure what Katsuki expected to find that he couldn’t have felt with his fingers. The former human was surprised that Katsuki hadn’t just slid inside. Did he want to make sure Izuku’s body was ready for it?But then Katsuki was mouthing the swollen scales. It was impossible not to writhe under the exploratory tip of Katsuki’s tongue. Izuku’s fins fanned themselves over the soft sand beneath them while his body tightened and released as he squirmed against the sensation. Even then, Katsuki’s fangs managed to avoid the soft scales while his lips teased the area. Izuku whimpered pitifully. His eyes were half-lidded as the tip of Katsuki’s tongue began to trace the edge of each scale lining his slit. He couldn’t even begin to understand how he could feel so much through those little scales. Would it feel this way on any other part of his body? He wasn’t sure he would survive if it did. Izuku was flushed scarlet as that clever tongue began to pry the lips of his new opening apart. He could feel his pulse in his gills as they worked overtime to bring enough oxygen to Izuku’s addled brain. When Katsuki’s tongue entered him, Izuku thrashed. He hadn’t meant to; it was purely instinctual and spurred by his apparent reactivity. Powerful, clawed hands pushed Izuku’s hips into the sand and held him firmly while his tongue made its way deeper. At first, Izuku was too distracted by the rising heat in his blood to appreciate its texture, but soon all he could think about was the incredible control Katsuki had over his tongue. Unlike his dick, Katsuki’s tongue was perfectly smooth. The tip had a sharper point than a human’s, and it was so, so long. The tip itself was agile, and it seemed to explore every little crease in Izuku’s new body. Each time it found a new place to explore, Izuku found himself keening in his overwhelm. The omega clawed frantically at the sand, if only to remind himself that he might hurt Katsuki if he reached for the alpha without thinking. This body was no longer human, and Izuku had to be careful with his mate. All too soon, Katsuki had leaned in so far that his lips were once again brushing Izuku’s swollen slit. Izuku’s inner walls welcomed him in. Unfamiliar muscles pulled at the intrusion, as though he badly wanted his mate even deeper.If there was heat in his blood, then there was fire building in his core. It ached with such need that it almost hurt inside. Katsuki’s tongue felt exquisite, but it wasn’t enough. There was an emptiness in his gut that had to be satisfied. Crimson eyes flickered up to meet Izuku’s, and the omega could swear that Katsuki knew exactly what he was feeling. The alpha growled low in his throat, and the tongue lodged deep inside transferred those vibrations to Izuku’s core.Izuku’s vision went white. He pushed his hips upward with enough strength to break Katsuki’s hold on his hips. It was probably only some miracle of siren evolution that he didn’t break Katsuki’s nose with his desperation to get closer, and, still, Izuku felt lips curl upward into a smile against his belly scales. The alpha’s hum deepened, and Izuku came undone. His entire body seized with the strength of his release, and his claws found Katsuki’s shoulders and clung; the omega having long forgotten to be careful with them. His body trembled as he came down from orgasm. It was almost magic the way every muscle first tensed and then slowly went boneless. His thoughts went soupy and lazy as he relaxed into the sand. He was still pulsing with heavenly aftershocks, and Katsuki held him through every sweet pulse. His nerves felt raw as Izuku’s breathing evened out, and his alpha began to withdraw his tongue. Izuku whimpered again at the emptiness, but it was also a relief. The former human was already so overwhelmed, and he wasn’t sure he could have taken much more without some sort of break. He opened his arms to invite Katsuki closer, and the alpha crawled obediently over him. His mate settled easily into his embrace, and their lips met in tender greeting. Cheekily, Katsuki swept his tongue into Izuku’s mouth. There was still something slick and viscous on the alpha’s tongue, and Izuku found himself happily sucking it off him. Knowing that he was tasting himself there made him whimper with delight. Somehow he wasn’t expecting it when the head of Katsuki’s forgotten dick found his slit. Even the light touch made him jolt. He chirped and writhed even as Katsuki pressed his weight down on him. “So sensitive,” Katsuki praised. “Much more sensitive than most.” The alpha siren leaned closer and nosed at Izuku’s gills. Izuku took a few gasping breaths even as he tilted his head to the side to give his mate more room. “Can you feel how much I want you, Deku? How much it fucking turns me on?” Katsuki growled low for him. The vibrations themselves seemed to add to Izuku’s teasing as they thrummed through delicate, new gills.
He could feel it.
He could feel Katsuki’s dick against him. It was so much hotter than even the burning at his core, and thick precum seemed to stick to his scales as Katsuki rubbed the thick shaft over Izuku’s tail.“Please… Tell me I can…” Katsuki begged. He drew his hips back and rubbed slowly up the length of Izuku’s body. His cock head caught ever so gently on the slit again. Izuku almost arched his hips to get it to dip inside, but Katsuki was pulling back before he could. “Tell me, Deku,” Katsuki ordered. “I need to hear you say it.”Izuku smiled through his own gasping. Explicit consent seemed to his mate’s kink. Since the moment they’d meant, Katsuki was always asking permission. Begging him for something Katsuki wouldn’t take; something that could only be offered. Izuku couldn’t have been more ready to give.“Katsuki, take me.” Izuku could feel just how tightly wound his mate was. Every muscle was taut under his fingertips as Izuku stroked his alpha’s arms, but his mate still entered so slowly and gently. Just the head slid past the opening at first, and it was all Izuku could do to hold still. Katsuki’s dick felt hot against his inner walls. It was nothing at all like the alpha’s tongue, which had seemed to match the omega’s internal temperature. The heat urged Izuku’s passage to relax and invite his mate in even as it made his abdominals tense with arousal. Izuku struggled to breath as Katsuki pushed a few more inches inside. He couldn’t afford to have all the breath knocked out of him now, or he’d pass out before Katsuki reached the place that pulsed at his center. He felt split open and overwhelmed. Katsuki’s length had dips and swells and frilled ridges. He felt the rippling around each ridge so deeply as they sank into his body.He might have guessed that Katsuki’s dick was prehensile. Every other part of his body had an inhuman level of control, and now the head of the alpha’s dick was prodding and testing his insides. The ridges seemed to pulse and wriggle as though they were trying to dig their way deeper. Izuku couldn’t stop clenching down experimentally just to feel how they’d respond to the extra pressure. Katsuki gasped over him and let out a long, slow breath. He held still for just a moment, and Izuku took the moment’s recovery to lick at the alpha’s jaw. Katsuki crooned for him, and Izuku could hear the praise and pleasure in it. The alpha pushed in a little further, and Izuku could swear that it grew inside him as the alpha’s dick rippled and pressed deeper. Katsuki’s muscular tail flexed and pushed, and several more inches pressed in all at once. That did knock the breath out of Izuku, but it didn’t reach the place Izuku badly wanted it to go. Now he sat at the swollen knot at the base of his mate’s length. The soft nubs there began teasing Izuku’s slit, and the omega whimpered weakly in response. It wasn’t fair that he could feel so much. Katsuki hadn’t even begun thrusting yet, and Izuku could barely see, because his eyes were so hazy with pleasure. His slit was puffy and swollen and the nubs caressing and pressing at the stretched opening was so good. Izuku mindlessly ground down on them, and the knot pushed at his opening and left him pleasantly throbbing. Something at the back of his mind told him that he badly needed to get those nubs inside him, but he wasn’t sure how he’d ever manage it. The knot beneath them was huge, and Izuku was already so full that he couldn’t hold still for the amount of pressure against his inner walls. “Focus on me, Deku,” Katsuki crooned, and Izuku’s eyes obediently found crimson again. The smile on his mate’s face was soft with affection as he pulled back and thrusted forward.The new movement instantly took the pressure off and left Izuku feeling relaxed as Katsuki picked up a rhythm. Their scales slid together easily as Katsuki’s tail moved over Izuku’s. Each thrust seemed to pull at some unseen inner current. It felt like sweet heat swelled at his core with such strength that it left him dizzy, and the greater that pressure became, the better it felt.Soon Izuku could barely think past the colors sparking behind his eyes. “Just focus on me,” Katsuki purred.His mouth found Izuku’s, and their lips moved together eagerly as Katsuki moved with him against the den’s floor. The soft grains of sand felt heavenly against Izuku’s skin and scales, but Izuku liked it even better when Katsuki’s hands sought his. Their fingers laced, and Katsuki used that grip to pin Izuku to the ground while he increased the strength of his thrusts.The current raged in his very blood now. His orgasm was building differently than it ever had before, but Izuku knew exactly what it was. He pulled away from Katsuki’s mouth so that he could cry out loudly as he came. His vision whited out with the strength of his release. His body trembled in the aftershocks while his mate snarled over him. Izuku was relaxed enough now that he thought it might be possible to get the knot inside, but Katsuki didn’t even try. Instead, he carefully ground down just enough that Izuku’s body began to part around the knot; teasing its entry, even though he wouldn’t push forward enough to risk popping it inside. It set the head of his cock even deeper. It teased that white hot space inside him and made pleasure rocket through Izuku’s system again. If he hadn’t just cum, he was sure that would have set him over the edge. Katsuki kept thrusting. Kept teasing that spot, rubbing it at just the edges and driving them both wild. He gripped Izuku’s hip tightly to keep him from squirming downward as he began to lose his own control.A deep throbbing began as Katsuki joined Izuku in orgasm. Seed flooded Izuku’s new body, and the tight pressure at his core seemed to spread out into a soothing pool of gentle warmth. It left Izuku feeling hazy and sated. Katsuki nuzzled into the junction of Izuku’s neck and shoulder and began lazily licking the raised skin where he’d delivered the bonding bite. “I love you,” Katsuki hummed against his omega’s skin. Izuku could hear the promise in those words, and the omega found himself getting emotional as he nuzzled closer. “I love you too,” Izuku promised almost desperately. He loved this man so much that having him buried in his deepest recesses was almost a religious experience. Izuku had no basis for human sex, but there was no way it was any better than that. The omega could easily get addicted to this.Already, just the idea of losing his place at Katsuki’s side felt like it might kill him, and that probably wasn’t far from the truth either.
BONUS!
Check out this wonderful fanart from my good friend Tephura! I am completely unworthy of her, and so, so happy! I think this may be my first ever official fanart, and my heart is so warm about it!
----- CHAPTER BREAK -----
For many days after their first coupling, Katsuki attempted to keep Izuku close to the den. They left the safety of their home to learn to swim among the corals together, but the alpha bristled furiously any time he sighted another siren in the distance. He was always quick to bring Izuku back to their den, even as Izuku struggled to get a better look.It didn’t take long to realize that Katsuki was trying to keep him away from the tribe. Social anxiety prickled under Izuku’s skin, but his curiosity was stronger. He wanted to see the other sirens. He wanted to know how they lived. He wanted to know their colors and mannerisms and beliefs; to experience his new community. He wanted to know how the others varied from Katsuki. Izuku was never going to leave his mate. He felt the truth of that in his bones. Whatever came next, the two of them were in it together, and Izuku needed to know more about Katsuki’s life. He had to have some idea of what their future might look like, and he wasn’t going to learn anything new while curled up in the relative safety of their den. He couldn’t let Katsuki keep distracting him with sex either. As much as Izuku was hungry for it, there had to be more to life than indulging their seemingly endless lust for one another several times a day.Izuku waited until his mate was relaxed and pliant under his hands to bring it up. The alpha had been on edge and extremely protective since Izuku’s change. A hand or fin was draped over Izuku at all times, as though the other siren was afraid Izuku might slip away without his noticing. His alpha was only just waking, and Izuku was tracing his pectorals with idle claws. Crimson eyes blinked open lazily, and the arm around the omega’s middle tightened. The blond hummed in greeting and nosed closer to nibble on his mate’s jaw. Izuku tilted his head back and happily let Katsuki’s fangs travel along his throat.“Katsuki,” Izuku started. His fingers found blond spikes, and the alpha eagerly leaned into his touch. “What do you need, Deku? Are you hungry?” Katsuki rumbled.“I want to see where the tribe lives,” Izuku answered instead. “We can’t stay here forever. You’re going to want to see your family and friends again.”The alpha tensed. Izuku felt a little mean for ruining his lover’s hazy contentment, but something had to change. There were a few moments of silence before Katsuki released a long sigh. His fluttering gills tickled Izuku’s arm as the omega soothingly stroked his mate’s nape. “I won’t. You’re all I need.”“That doesn’t work for me, Kacchan,” Izuku argued even as he nuzzled closer. “Please? I want to see what life is like down here, and I won’t really know what to expect until I meet your family.”His alpha blinked slowly and clicked in irritation. It took a few moments more before he made a hesitant noise of agreement. Katsuki’s fingers brushed back green curls as Izuku snuggled gratefully closer to his mate.“You’re learning to hunt first, and we’re practicing your swimming,” Katsuki insisted. His eyes narrowed with determination, and Izuku could feel a spike of anxiety in their bond. The omega frowned as he considered that reaction. The confrontation with Katsuki’s mother was still fresh in his mind. Was the entire tribe the same? Did they think of him as a weak human who had condemned one of their strongest warriors?“Do I need to?” Izuku questioned. Viridian eyes found his alpha’s again as he searched the man’s face for insight. “Yes, Deku. No matter where you are in the ocean, you should be able to defend yourself or escape as needed. I won’t let any of those vicious bastards near you until you know the basics.”Viscous bastards? Izuku swallowed nervously. Somehow, he was still expecting the other sirens to be like Katsuki. He was rough around the edges maybe, but his heart was good and loyal. Izuku couldn’t help but hope that he would have some friends among them.“Come,” Katsuki ordered.A now familiar hand found Izuku’s as the alpha led him toward the entrance of their shared home. Katsuki had much better control over his body than Izuku, but the omega was learning by allowing Katsuki to guide him along. The alpha slowed at the entrance and gave Izuku the opportunity to lead through the more familiar grounds. Izuku’s pulse raced every time they left. He wasn’t sure he would ever get used to the new world around him. The ocean was more full of life than he’d ever imagined. With a siren’s eyes, he could see the light filtering through the water even at this depth. The world around them was colorful to his new senses. Seagrass waved lazily with the current, and brilliant corals clung to the rocks that rose from the ocean’s bed. Izuku had known, as a concept, that he had been surrounded by life on land. The ground teamed with bugs, the air with birds, and small animals lurked in every alley and behind every crate. And yet, he’d never been aware of them the way he was of the creatures buzzing about him under the water. The fish were numerous, but there were also creatures crawling through the sand and clinging to the foliage. Most of the animals that dared spend time around Katsuki’s den were too small to warrant notice. Katsuki always took him further out and into more open water to swim and hunt.Izuku did his best to ignore the environment and focus on his swimming, but it was so easy to be distracted. Movement was no longer focused on his legs. Instead, it was a full body experience, and so he had to pay attention to the entire area around his body instead of what was just in front of him. It was disorienting, but he was getting accustomed to it. This body knew how even if Izuku didn’t. His fins picked up on every minute movement around him as long as he was relaxed enough to pay attention. Katsuki took over once they’d moved beyond the rocky outcroppings that surrounded their home and into the more open corals beyond. He swam under Izuku for a bit and pulled him along while the omega enjoyed the way the water cut around his new body. Izuku smiled down at his mate. Katsuki was going to be a wonderful father someday; if it was really possible. The alpha was an endlessly patient teacher, and the omega was trying to reward his efforts by studying diligently. Katsuki eventually guided them into an area of reef that was surrounded by thick seagrass and settled in among the long strands with his mate. Izuku smiled softly as the strands encased him while he nestled in with Katsuki. The alpha leaned close to whisper in his mate’s ear, and Izuku did his best to focus on the advice instead of the way Katsuki’s lips brushed his skin. “Taking them by surprise is probably your best bet. If your scales harden, we’ll try full, frontal assault. Until then, you have to do your best to chase and stun,” Katsuki explained. He moved some of the grass aside to give Izuku a better view and then began to point around their new environment while explaining the plan.“I want you to wait until something worthwhile passes by. Then you’ll swim after it as fast as you can until you can push it into a crevice or the sea floor. It’ll be easier to use force to get them into the right spot than to try to catch them in your claws.”Izuku nodded his understanding, and Katsuki lowered himself all the way to the ground to wait. Seagrass swayed over his back and kept him mostly hidden from view. His body went very still, and Izuku did his best to mimic his posture. Everything around them went quiet for a few moments. It gave Izuku time to center himself as he waited. He tried to think of a plan, but he got the impression that instinct might be a greater help. It wasn’t long before a decently sized school of fish swam by. At the first sight of them, Izuku darted into action. Maybe these were too small for the stun technique to work, but he had to try. His world narrowed down to the flashing, silver fish as they raced away from him. Perhaps he was too focused, because he ended up slamming into a rocky bank at full speed. Izuku hissed in pain as the sharp stones damaged his soft scales. Katsuki was by his side in an instant. Izuku had expected his mate to berate him for making such an amateurish mistake, but, instead, the alpha was quiet as he checked Izuku over for injuries. Careful fingertips prodded the new scrapes and wounds. Some of the stones had broken past the scales and left tender flesh exposed. Izuku’s eyes narrowed. If that was all it took to damage him, then just how soft were these scales? They couldn’t be much harder than human skin, and that was dangerous.Katsuki didn’t mention it. Instead, he leaned in to kiss Izuku’s forehead. “I should have warned you. You should look when you can, but it’s easier to feel the flow of the water and follow it rather than keeping track of the landscape when you hunt,” Katsuki explained. He leaned forward to rest their foreheads together, and Izuku slowly began to relax again. Being close to Katsuki always made him feel better; more centered. “I can do this,” Izuku promised. He wasn’t about to let soft scales get in the way of their life together.“I know you can,” Katsuki answered with obvious pride. His mouth stretched wide to reveal every one of his shining fangs.He took Izuku by the hand and led him back to the bed of grass. They rested there longer this time. Izuku was, in essence, a large predator, and many of the animals had scattered after his charge. It took time for them to return to the reef. The pain of his new bruises faded to a dull ache while he waited for a larger target. When a viable option came by, Izuku rushed it. This time, it was a single, large fish. Maybe too large for his first kill, but Izuku needed something he knew he could hit. The damn thing was still faster than Izuku had expected. For something so large, he’d expected it to be clumsy, but that couldn’t have been further from the truth.Izuku wove through the landscape easily, allowing the current flowing past his fins to guide his movements. He’d barely realized that he’d cornered the damn thing when he smacked the creature into a rock. The creature went still. Its gills still moved, so it wasn’t dead, but it had been stunned on impact. Izuku didn’t give it time to recover. He ripped into it viciously. It didn’t occur to him until he’d already swallowed that this was the first time he’d fed without Katsuki’s help. Something about tracking the fish down himself had taken the initial disgust away. Perhaps seeing the fish living in its own environment had rewired something in his brain. He didn’t think of fishing boats or open markets anymore. Instead, he thought of vibrant corals, seagrass, and schools of fish that shimmered even in the low light. When his mate came to join him, Izuku eagerly turned to share a mouthful of his first catch. Katsuki trilled with victory and took a bite of his own. They ate the kill together until it was little more than bones, and then fell into the sand happy and satisfied. Izuku was starting to wonder if they should go home when he turned and found Katsuki smirking at him. The alpha was on him in moments, and the tinkling sound of siren laughter filled the water as the two rolled together across the sandy floor. Izuku did his best to pin his mate, but Katsuki was larger. He wasn’t afraid to use his muscles either. Izuku had to get creative to keep the game going. They wrestled until they were both panting and smiling in the high of their success. Izuku rolled on top of Katsuki one more time as they panted. He leaned in and kissed Katsuki deeply, only to find himself rolled on his back again as Katsuki curled around his body. “You were so beautiful,” Katsuki praised. The blood red of his eyes narrowed with affection as they explored Izuku’s face. “I know this is all new, but you looked so natural. It’s like you were always made for this.” “Maybe I was,” Izuku purred for him. Satisfaction curled in his gut when he saw the alpha’s pupils dilate with pleasure. Katsuki wouldn’t admit it, but he loved any acknowledgement that they were destined. “I feel like you deserve a reward,” Katsuki rumbled. The coil of his tail loosened so that he could slide down Izuku’s body. The sweet brush of their soft belly scales made Izuku’s breath hitch. That was usually a precursor to sex, but they weren’t in their precious den. This was open water.
Surely, they weren’t going to do anything here?
Katsuki nosed the opening in his scales, and Izuku felt like his whole body was starting to blush. When the alpha prodded his slit, Izuku squirmed in his arms.“What’s the matter, Deku? Too much for you already?” Katsuki teased. “Anyone could see us here!” Izuku hissed back, but his words lacked any real bite. Instead, he was sure his clicks betrayed his embarrassment, because Katsuki’s expression grew smug. “Wouldn’t that make them lucky?” Katsuki teased. Izuku covered his face with his hands, and Katsuki reached up to gently pry them away. “Are all humans so prudish?”“S-Sex is private for humans. Maybe they are prudish. There are a lot of expectations about who you can have it with, when, and where…” Izuku tried to explain through little clicks and warbles. All the while his mate watched him with far too much amusement. One of the alpha’s fingertips brushed over Izuku’s opening. It caught ever so slightly on the folds and pushed the scales apart to expose the pretty, pink passage underneath. Izuku’s flushing grew worse at the proof of his own arousal. He knew from experience that the scales didn’t part at all when he wasn’t feeling receptive. “No one is going to bother us here,” Katsuki promised.His brilliant eyes flashed with arousal, and Izuku wished he could open himself even further. What could ever be more important than this? He’d take Katsuki anywhere. He released a soft croon of acceptance, and his mate eagerly lowered his head again. This time the tip of his tongue breached Izuku immediately. The omega arched upwards into him and marveled at how deep Katsuki could reach. His long tongue caressed the inner walls slowly, and Izuku couldn’t have kept still to save his life.The omega hadn’t gotten any better at this. He was still at Katsuki’s mercy every time his hands or mouth were on him. His alpha pulled back just enough so that he could curl the flat of his tongue against his opening, and Izuku wailed. His claws sought purchase in the sand, but there was nothing to grip that his claws couldn’t instantly shred. Mercilessly, Katsuki’s tongue pushed all the way in again, and the blond’s lips teased the omega’s belly scales while that sinful tongue mapped his inner walls. “I-I need more!” Izuku begged. He did need more. For all the sex they’d had, that white, hot spot inside never seemed to be fully satisfied. It would calm for a moment when Katsuki made him orgasm, but it was never quite enough. His lower lip quivered, and he had trouble focusing as he looked at Katsuki. He was already overwhelmed, but his body yearned for more. He badly wanted to be full again. He almost cried when Katsuki’s tongue withdrew and left him empty.“You want a knot,” Katsuki rumbled. It was a statement rather than a question, and Izuku didn’t even try to deny it. “H-Humans don’t have them… B-But when you tease me with it, it’s like… It’s like you reach something new,” Izuku tried to explain. He was filtering water so quickly that it was affecting the currents around him, and Katsuki seemed to enjoy watching him squirm and pant far too much. “It’s because I’m close to entering your womb when I do,” Katsuki informed. “You what?!” Izuku exclaimed. He sat further up, and his mate happily crawled over him and nuzzled his cheek. Izuku leaned into the caress and pressed a few kisses to Katsuki’s face in turn. “Why so surprised?” Katsuki questioned. “You must have noticed. It feels different. Better?”“Humans can’t do that,” Izuku explained. His eyes fluttered shut as Katsuki’s lips found his neck. He was always very careful around his gills, but he also liked to nibble and suck at the sensitive areas around them. “I didn’t even have a womb until you turned me.”“Sirens can breach the womb, but only when knotting. It’s the best way to reach and fertilize eggs, but sirens rarely trust their partners enough for it,” Katsuki explained. Izuku reached down to rub Katsuki’s length. He didn’t need to tell his alpha just how much he trusted him. Their bond thrummed with the strength of the trust and love between them.“Why?” Izuku rumbled even as he guided Katsuki’s dick to his opening. The alpha moved slowly forward so that Izuku would feel the glide of every one of their scales as he did so. His length slid half way inside, and Izuku arched his hips to force it in just a little further. Izuku’s eyes fluttered as his body welcomed the familiar flutter and pulse of his mate’s length. He rocked back a few times to entice Katsuki deeper, but the alpha insisted on keeping the slow, gradual glide.It was too slow for Izuku. He could already feel the way his natural lubrication began to escape and gum up around his belly scales. He was ready.“To be stuck together in the tie is dangerous,” Katsuki explained. He nuzzled into the side of Izuku’s neck. “It takes trust to go through with it for unbound pairs.”“Why? Isn’t it dangerous for bonded pairs?” Izuku questioned. He blinked hazily at Katsuki while his alpha slowly eased the rest of the way inside. He wanted it faster, and he knew his mate was teasing him. “Yes. It might be dangerous if they were ambushed, but the tie is mostly dangerous because one siren may kill the other. We kill each other for many reasons, but especially for social standing. The sirens in a tie are both held in place and high on endorphins,” Katsuki explained as he finally began to thrust.His voice was melancholy, but the bond between them was full of comfort and affection. “They… Kill each other?” Izuku asked, horrified. He clung to the comfort that Katsuki offered, and relished the way he stilled so that Izuku could focus on their closeness. “It’s cowardly, but it does happen,” Katsuki admitted, “As the tribe gets more desperate for pups, it becomes more of a concern.”Izuku wrapped his arms around his mate’s neck and pressed his hips down so that he could grind against the knot. Just feeling it against his entrance reignited the fire at his core. He was so fucking glad they were bonded, because he was pretty sure he needed it. “I love you,” Katsuki crooned as he picked up the pace. Izuku arched eagerly into his thrusts. The frills and ridges of Katsuki’s dick were a wealth of sensation when Katsuki’s pace was slow, but it turned into intense friction when he sped up. Much of his tail already ached with forming bruises, and Izuku couldn’t bring himself to care. He wanted Katsuki to bruise him. He wanted to be marked in every way possible, and he wanted to mark Katsuki in return. Stubbornly, the omega clung to Katsuki and began biting and sucking at his chest and shoulders while pushing insistently on the knot. The little nubs at the top of the knot, which Izuku had since learned were villi, rubbed happily at his slit and sometimes slid inside to stimulate the inner walls and help them prepare for the oncoming knot. “Kacchan… Please,” Izuku begged. Just the initial stretch was making him twitchy with excitement. His body was unable to keep still when it was so eager to finally be full. “Net yet,” Katsuki argued. Sharp fangs scraped along Izuku’s jaw and worked their way up to one of his ears. “I want you to come for me first.”Izuku whimpered and curled his tail more firmly around Katsuki’s. It slowed his thrusting marginally, but the bind itself was its own sort of pleasure, he’d learned. Pressure brought pleasure, and Katsuki’s dick wasn’t limited to thrusting in and out. It could move and pulse and ripple. It brought them both pleasure whether they were moving or not. Izuku wasn’t sure he wanted to cum. His body relaxed when he did, but it also made every sensation feel like it had an echo. He wasn’t sure he wanted to take his first knot while oversensitive.Katsuki was smirking at him, and so Izuku knew that the alpha could tell exactly what he was thinking. But Izuku was tired of letting the alpha win. He was still new to this, but he’d learned a lot already. The omega constricted further and rolled them. He growled down at his alpha in a playful challenge, and he felt Katsuki through their bond trying to assess how badly he wanted to win. This was Izuku’s day. This had been his first kill and would be his first knot, and he wanted to win badly. They rolled a few more times, ironically pushing the knot deeper as they did. The tinkling sounds of laughter filled the clearing again, but Izuku pushed down hard to signal to Katsuki that he was ready to end the struggle.The alpha looked up at him quizzically, and Izuku growled low. He gave his alpha a bright smile, but his eyes were over-bright as a wicked impulse entered his mind.There was only the barest warning across their bond before the omega bit deep into Katsuki’s shoulder. They were already bonded, but Katsuki may as well have a mark to match. Blood sweetened the water as Katsuki went lax in Izuku’s coils, and the omega used the opportunity to push down hard. There was a faint burn, but Izuku scarcely noticed it as the knot finally, finally slid into place.Izuku wasn’t sure what he was feeling at first. All he knew was that Katsuki’s dick had slotted into something divine. It felt so good, so important, that Izuku couldn’t process anything else. No touch, sound, or sight registered, because everything he had was focused on what was happening in his womb and in their bond. Katsuki’s knot grew even larger once it was fully encased. The flesh pulsed and bloomed outward to lock Izuku in place. His dick wedged perfectly into that hot spot inside the omega, the one that seemed to constantly ache with need. Izuku clenched down around it eagerly as new muscles made themselves known. It was as though his body moved on its own. His inner passage rhythmically stroked the flesh inside him. He felt Katsuki’s length in new ways as his body caressed him, and Izuku was struck by the knowledge that he probably had just as many thrilling muscles and frills and moving parts within him as Katsuki’s dick did. Katsuki was coming. Izuku could feel his mate pulsing in response to every firm pull of Izuku’s inner walls, and, more importantly, he felt the hot semen filling up that place that had been so, so empty. It was like spreading aloe over a burn. The ache inside was long forgotten as every hot jet of Katsuki’s release soothed Izuku’s instincts. The omega was certain that Katsuki’s semen had never reached him this deeply, because it had never felt this way before. His cum was locked up inside him with nowhere else to go. It filled him eagerly and completely, and the steady stream of it showed no signs of stopping.Somehow, the sensations coming through the bond were even better. All barriers between them seemed to have come down as soon as the knot settled inside, and now Izuku could feel Katsuki’s deep-rooted satisfaction and delight as though it was his own. Izuku could feel the echo of his mate’s pleasure with every pulse in each of their bodies. He could feel how Katsuki delighted in the echo of Izuku’s pleasure as well. The alpha was awash in pride knowing that he’d knotted and filled his mate; thoroughly satisfying him in an entirely new way.It was a feedback loop of pleasure that they were both happily lost in.Their senses came back to them very slowly. Izuku couldn’t even have guessed how much time had passed. Katsuki had been right about knotted sirens being vulnerable. Izuku wouldn’t have noticed anything through the pleasure of it, and it made him wonder if this was more dangerous for bonded pairs.Izuku reached between them and found the soft spot that Katsuki had identified as distinctly omega. It was softly swollen outward with the volume of Katsuki’s release, and just looking at it made Izuku rumble with pleasure.He hadn’t expected so much more cum compared to their usual coupling, but he also found that he liked it. He allowed himself a moment to imagine what was happening inside him; how the tip of Katsuki’s dick was still tucked safely inside his womb and still occasionally delivering another jet of seed. He imagined the womb closing behind his mate and leaving his essence trapped inside for hours after.How long would it take to leave him? Better yet, how long would it be before he had eggs for Katsuki to fertilize? How would it feel to swell with the proof of their coupling?His mate rolled them again, but this time he did it so that Izuku could affectionately nuzzle into Katsuki’s neck while he lounged. His alpha lazily stroked green curls while they rested in post-orgasmic bliss. “Kacchan… You do have friends, don’t you?” Izuku questioned. He hadn’t considered that Katsuki may not have friends he wanted to visit, but he was beginning to understand that sirens were often violent and untrusting. Real friendship might be rare in their culture. “Only a few,” Katsuki confirmed. “Denki and Eijiro are the closest to me in age, and I like them best. I have a passing friendship with some of our other hunters, but we also fight for standing. It will never be the same.”Izuku hummed as he contemplated that. Only two friends that Katsuki would address by name. It didn’t seem like many, but it might be enough. Friendship was never about quantity on the surface either. Even one truly good friend was enough, and Izuku already had Katsuki. “I thought we could visit Denki first. He is an unmated omega, and a bit of an outcast himself. He’s fascinated with humans and mostly non-violent. He falls low on our hierarchy, but I think you will like him.”“You said you like him, right?” Izuku prompted. “I said I trust him. At least a little, but he’s dopey and mostly useless,” Katsuki argued. The omega gently swatted his mate’s chest. “That’s not nice, Kacchan.”Katsuki smiled widely at his mate, and leaned in for another sweet kiss. “If he makes you smile, I’ll have to change my mind,” Katsuki promised, and Izuku could hear the truth in it. After all, Katsuki would love anything that made Izuku happy.Their lives were tied together now, and Izuku wouldn’t have it any other way.
----- CHAPTER BREAK -----
It took a few more days to convince Katsuki to take Izuku further into the tribe's territory. The alpha insisted they wait until Izuku’s scrapes and bruises were healed after his first hunt. He spent the time meticulously grooming his omega’s scales and massaging his aching body. The alpha looked self-satisfied and pleased as the new scales grew in. He insisted that they were harder and darker, but Izuku thought he might be imagining it. The flesh still looked unpleasantly milky to him, but Katsuki continued to treat him like he was the picture of perfection. It was hard to believe how different his life had become in such a short time.The depression of the mainland seemed so far behind him. Izuku’s heart still ached whenever he thought of all he’d lost, but it was an easier weight to carry with the promise of the future ahead of him.Izuku lay curled in the sand with his mate. He hummed a low, siren’s melody while stroking Katsuki’s blond spikes. The alpha’s eyes were hazy, and his body rested in a loose curl on top of Izuku’s so that their scales brushed together lazily every time their bodies shifted. Katsuki was always like this when the omega sang for him. All the tension and aggression bled out of him and nothing but contentment was left behind. Just watching the shift in his mate’s demeanor brought Izuku joy, but the feedback through their bond was even better. Every note seemed to build the satisfaction between them.“I still want to meet everyone, Kacchan,” Izuku reminded. His mate stiffened minutely against him, but he didn’t shift away. “Everyone here is dangerous for you. I don’t fucking like it,” Katsuki admitted. The alpha turned and pulled himself further up Izuku’s body so that they could talk face-to-face. His crimson eyes were narrowed with a grim sort of acceptance. Izuku wished it could be easier for them both, but they were going to have to face this eventually. “We’re starting with your friends, aren’t we? That should make it easier,” Izuku attempted to comfort. “I fucking guess! But I still don’t…” Katsuki growled low in his chest, and Izuku smiled as he placed a hand over his mate’s heart. He could feel the vibrations of his lover’s growling in his fingertips.“You don’t want to share,” Izuku accused. His fanged grin widened as he watched his mate blushed brightly. His scales flashed bright orange, and his fins flared with his flush. Katsuki was usually so self-assured, but he really was beautiful like this.It wasn’t so long ago that death hadn’t felt like such a terrible thing. And now he had Katsuki.How could he have gone without knowing Katsuki? Izuku’s heart fluttered, and Katsuki clearly felt the way his emotions wavered. Clawed hands drew Izuku’s body closer for an embrace. Even his tail wrapped a little more tightly around Izuku as they lay tangled together.“I need to feel integrated, Kacchan. I want to feel like we have a future here together,” Izuku continued. Katsuki’s growling mellowed into a low rumble, and Izuku closed his eyes and let the comfort seep into his very bones. He only wished that everything could be as easy as their bond was. Loving Katsuki was effortless. It was hard to believe that anyone could oppose something that felt so right.“No matter how things go with them, we do have a future. It’s you and me, Izuku. Always,” Katsuki promised, “There’s not a voice in this ocean or world that could convince me otherwise.”Izuku rolled them in the sand and rubbed his face against his lover’s shoulder. Katsuki’s claws tangled in his curls and happy clicks filled their den as joy echoed between them. “You’re ready. We can go see dunceface today. He lives on the outskirts, so it shouldn’t be too dangerous for your first visit,” Katsuki explained. Izuku trilled his excitement. Maybe he shouldn’t have been so eager to meet more unknown sirens after he’d been nearly torn to pieces, but he wanted it so badly. Some part of him felt like he had something to prove. He could belong in this life. He could do anything for his Kacchan. The alpha checked Izuku’s scales meticulously one more time before they left, and the little smile he wore told Izuku that he thought they were still hardening. He hoped it was true. He knew Katsuki would protect him, but he couldn’t help but feel anxious when he thought about how easily he’d been damaged.The anxiety only grew as they left their den. Izuku was eager to learn more, but the ocean was very different to his life on land. Everything before him was so vast, and it faded into a dark blue haze on the horizon. It was still disorienting, and he didn’t know the landmarks that would help him find his way back.A wave of reassurance washed through the bond as Katsuki took Izuku’s hand. The omega smiled up at his mate. He knew how much Katsuki wanted to crowd him back into the den and keep him there, but he was helping Izuku push forward anyway. He was so lucky. Affectionate clicks were on his tongue as soon as he thought it, and Katsuki pressed into his space with a smug smile. Their fins brushed as they glided past the rocky outcroppings, thick corals, and seagrass. Familiar ground was soon behind them, but it was hard to pay attention to the changing landscape while his alpha was openly flirting with him. Katsuki’s claws grazed his sides and hips teasingly as they moved, and Izuku’s entire body heated in response. For the first time, a glimmer of green entered Izuku’s scales. It left him elated and bold. He rolled them over so that they spiraled as they moved. The shifting current was liberating in his curls and fins, and Izuku laughed as his mate, ever competitive, spun them even faster. In their joy, they didn’t notice the danger until it was on them.A blur of pale gold struck them from the side, and they fell apart as they were thrown aside. Pain blossomed in Izuku’s side and bloomed in the bond he shared with Katsuki. Being thrown in the water was a lot more disorienting than it was on land.For a moment, Izuku didn’t know up from down, but he did know that it wasn’t his blood he could smell in the water. Even without the sharp pain in their mental link, his body seemed to know the scent of Katsuki’s blood. Sudden panic made Izuku’s body stiff, but he still managed to right himself.By the time his eyes found the attacker, Katsuki was already charging him.
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The other siren was puffed up, and his lips were drawn back to show off a mouth full of needle-thin fangs. He had dark claws and gray scales with hints of a pale yellow pattern. The combination of colors made the sheen of him look almost sickly, and there were a good number of pale scars running along his length.Like Katsuki, he was blond, and Izuku wondered for a moment if they were related. His hiss of rage was so high pitched that it hurt Izuku’s ears, and it was tinged with something that sounded like arrogance or superiority. He must not have seen Katsuki coming, because he charged at Izuku with lightning speed. Something bubbled in Izuku’s chest; something stronger than panic. The green in his scales flashed more brightly. He opened his mouth to scream, but even that wasn’t faster than his Kacchan. Katsuki scales flashed brilliantly as he set upon their attacker with claws and fangs all at once. He twisted beautifully in the water, and the spines along his body tore through the other merman’s side. When Katsuki lifted his head, he came away with a sickly chunk of flesh in his jaws. He spat it out as though he’d tasted garbage, and the other siren turned and swam away to make room between them. Izuku watched, shocked, as Katsuki turned to follow the retreating siren. The alpha’s claws bit so deep into the other siren’s back that ribbons of sickly flesh were left caught in the current as he ran.“It will be your fingers next!” Katsuki threatened.Blood filled the water, and Katsuki released a few triumphant screams in their attack’s wake before returning to Izuku. The omega shook with nerves as Katsuki checked him over. Claws, still coated with shining viscera, lifted Izuku’s hands delicately to check his fingers. His touches were sure and careful, but Izuku could feel that Katsuki was more shaken than he was. The bond was alive with panic even as the alpha brushed the flat palms of his hands over every surface of izuku’s body to check for damage. He left smears of the other siren’s blood in his wake, but Izuku didn’t have time to care.He began to hum. The vibrations were low but strong enough to shake the water between them. Izuku watched the way they affected his mate with calculating eyes. After all, Katsuki was the one who was injured. The alpha hadn’t noticed, because he was too busy fussing over Izuku.The omega threaded his hum with the barest hint of siren song, and Katsuki began to relax into his open arms. Perhaps one day, Izuku would be able to sing like his mate. Threading it in small ways like this seemed easy enough. He used the new sense of fuzzy calm to gently prod at his mate’s wounds without upsetting him. The alpha held very still as Izuku cataloged the damage. He was sure there were minor scrapes and bruises elsewhere, but the worst of it were claw marks in his side. Thankfully, the bleeding had already begun to slow. The wounds would seal quickly.“You okay?” Katsuki slurred against Izuku’s neck. He nuzzled in closer until the tip of his nose was tickling Izuku’s gills. “I’m fine, Kacchan. You’re the one who’s hurt,” Izuku promised. “It’s just a scratch,” Katsuki growled even as Izuku prodded the area. It really was just a scratch by comparison to what Katsuki had done to the other siren. He wondered how long the stranger’s deep gouges would take to heal. Surely, he wouldn’t bleed out. They must have something available to stop that. “We should go home,” Izuku suggested gently. He had a lot of questions, and he knew Katsuki wouldn’t want to answer them here. Their bond was prickly with worry and anxiety after the attack. “No,” Katsuki grumbled. “If we go home now, Neito will twist the story until it sounds like he pushed us back to our den… This is normal in our tribe, and this won’t be the last time we’re tested either.” “Neito?” “That fucker who challenged me. He’s a power hungry, little bitch,” Katsuki snarled with disgust. Izuku flinched and closed his eyes against the mental image of the siren’s ruined back. “You hurt him badly…” Izuku muttered. “It’s the only way! In this tribe, only power is respected. You have to hit fast and hard, and I needed to hurt him enough to discourage any of his fucking friends,” Katsuki explained. He shifted closer to nuzzle at Izuku’s shoulder. “That is the only way I can keep you safe.”Izuku could hear the worry in his tone, and he could almost feel the adrenaline bleeding out of them both. He turned into his mate and began to lick and nuzzle at his jaw. Katsuki rumbled his appreciation while Izuku’s hands slowly swept down the length of each arm. “I’m sorry you had to,” Izuku whispered to him. “Izuku, I have already killed for you, and I’ll do it again. I’ll do this as many times as I have to,” Katsuki promised. Bright, red eyes met dazed green, and Izuku gazed deeply into them while his mind raced to understand the depth of that statement. It hung between them, and, even after prodding the bond, Izuku couldn’t find any lie or shame in them.
Katsuki had
killed
for him?
It must have been the siren that lured him off the ship. How had Izuku not thought about it? He’d been so caught up in the transformation and the bond growing between them. The magic had woven through his new life effortlessly and somehow masked the violence that made it so. The siren with the pale eyes was dead, and Katsuki had done it quickly enough that he’d been able to pull Izuku to the surface before he drowned. And he didn’t regret it.“Was he… From your tribe?” Izuku asked. His fingers shook where they rested against Katsuki’s skin, but he was beginning to feel numb. Magic was easy to accept. Life under the sea came surprisingly easily, but Izuku didn’t know if he could adjust to this passive violence. He wasn’t sure he could abide by this lack of reverence for other lives. “No. He was a rogue. He’s adrift and forgotten now, or my mother would have pitched me shit for it.” Katsuki’s tone was sharp, but Izuku could feel his worry. He sensed the nervous exploration of their bond, and he knew how Katsuki withered when he found Izuku’s fear and doubt. “Would you… Be in trouble for it?” Izuku managed to ask. “Socially, perhaps. My mother has asked that we try not to kill each other now that our numbers are small. It’s made the fighting even worse, and we still kill each other.” Katsuki paused and leaned in closer to nose at Izuku’s ticklish gills. When he spoke again, the sounds were low and private. “Human or not, he lured my mate, Izuku. His quick death was a greater mercy than he deserved.”Izuku wasn’t sure how he felt about those words. He couldn’t begin to sort the chaos in his head, but Katsuki didn’t give him a chance to reply. The alpha took him by the hand and then swam forward. He kept them moving, but the joy from earlier was long gone; swept away with the currents.
----- CHAPTER BREAK -----
Katsuki tried to watch every direction at once while they swam. His body was tense, and the blood orange in his scales seemed to flash with every movement. Izuku was doing his best to help, but he still found moving underwater disorienting. It was made worse by his scattered, panicked thoughts and the oppressive worry and bloodlust coming through their bond.Neither of them calmed until Katsuki began to slow outside of what must have been someone’s den. It took a moment for Izuku to truly understand what he was looking at, because the dwelling was so wildly different from their own.No attempts had been made to hide it. Instead, a door of colorful, woven reeds hung over the entrance, and the area outside the little home had been cultivated. Colorful plants and corals grew around the den in artful, little arrays. Makeshift pots decorated the doorway, presumably to house the plants that wouldn’t grow directly on the sand. Just looking at it made Izuku’s heart swell. He hadn’t seen many signs of home since he’d joined Katsuki in the ocean, but the proof of crafting and cultivation gave Izuku hope. It reminded him, somewhat painfully, of returning home to the little house he’d once shared with his parents. He could remember what it felt like to run home to their small fence; to play with his father in the yard while his mother tended her flowers.He might never have that again, but he did have a home here. Already, Izuku had some new ideas on how he might make their den a little more his own. Katsuki released a few whistling clicks in greeting before they got too close. Izuku could scent the other siren here, and the prickling over his instincts was almost tangible. He could feel that this was someone else’s territory, and something told him that he should be cautious about approaching another omega’s den. He hadn’t consciously made an attempt to discern Denki’s sex, but the information was there at the front of his mind, as though there were hints of it permeating the very water.It wasn’t long before the woven door was pushed back to reveal a pair of quizzical, golden eyes. Izuku was taken with them immediately. They were a vibrant, molten gold in the darkness of the entry, and they were doubly bright for their curiosity. The siren whistled back and waved his hand to beckon them inside. Izuku tried to move forward, but Katsuki gently pulled him back. The alpha entered the den first, and Izuku was struck by the thought that he’d done it to check for danger, even though they were visiting a friend. He couldn’t help but wonder if life was always like this for sirens. Was there anyone Katsuki truly trusted?Frowning, Izuku followed just behind, and, in this new space, he could see Katsuki’s friend far more clearly. Denki’s tail was narrow and sleek, as though he were built more for speed than combat. The scales were near black, but he had a jagged streak of vibrant yellow along each side. His hair was a little yellower than Katsuki’s, and there was a unique stripe of black in on the right side of his hair. Most characteristic of all was the soft smile on his face as he considered them. “Katsuki! Is this your mate?” The siren asked with a rush of sweet excitement. The notes in his voice were bright with friendliness, and they filled the den with a sense of eager greeting. Izuku let the sound of it soothe his addled nerves. He could still smell Katsuki’s blood, so he was sure that Denki could too, but the other omega seemed content to ignore it. Izuku was glad for it. He knew how shaken Katsuki was, he was certain that the alpha wasn’t ready to discuss it yet. He needed time to unwind first.The two blonds chittered at each other, seeming to pass more emotion than sentiment for a few moments while Izuku looked around the den. He could hear a mixture of enthusiasm from Denki and exasperation from Katsuki, but Izuku was too enraptured with his surroundings to follow their conversation.Denki’s home was decorated and full of oddities and keepsakes. The rock walls had been carved back to create small shelves, and every one was full to bursting. Izuku recognized distinctly human items among them. There were a few glass bottles, shiny baubles, and coins. It was chaotic but charming. Baskets of woven seaweed hung from the ceiling. The nearest one was filled with crustaceans, probably for dinner, and others were full of shining rocks, plant stocks, or unfinished projects. In the corner, Izuku could see a woven hammock where the other omega must sleep. Everything was scented and worn and homey.“You really did it. I didn’t think it was possible,” Denki muttered as he approached. He reached out to take Izuku’s hand, but Katsuki growled low in warning. Denki swirled away easily, as though he were accustomed to such reprimands and scarcely needed to consider them before obeying. The reaction was perfectly submissive, and his easy acceptance had Izuku fascinated. He reached for Denki instead, and the change in the omega’s face when Izuku took his hand was stunning. Denki’s eyes widened and his smile spread as though he were being lit from the inside, and, suddenly, Izuku didn’t feel as alone anymore. “I’m Denki.” The siren greeted him in happy, little chitters. Izuku already knew that much, but he was quick to answer the greeting.
“I’m Izuku.” His answer sounded lilted and excited even to his own ears. He turned toward Katsuki with a bright smile, and the alpha’s expression was soft with relief. After their disastrous trip in, this introduction was going surprisingly smoothly. The anxiety began to ease from their bond as the alpha finally began to relax.“You were attacked on the way here?” Denki questioned. He tilted his head as he spoke, quietly offering more of his neck in a show of submission. He must be very accustomed to Katsuki if he knew the exact moment the alpha had relaxed enough to answer. “Neito,” Katsuki explained. His shoulders drew up further, but he didn’t growl or snap in his frustration. “Izuku, would you mind getting the bottle from the shelf over there?” Denki asked. To Izuku’s surprise, he offered the same placating gesture to him. His neck tilted sweetly as he spoke so that Izuku could see the fluttering of his gills, and Izuku found himself nodding easily. “What’s it for?” Izuku asked as he retrieved the bottle from the shelf.“It’s healroot salve. It dulls the pain,” Denki explained. He moved to the side to watch while Katsuki laid back for his mate. Izuku wondered if seeing Katsuki yield was a novel experience, because Denki was watching them with open fascination. Izuku coated his fingers in the salve. It was thick on his skin and gritty. He hadn’t been expecting the texture, but Katsuki seemed familiar with it. The alpha didn’t so much as flinch while Izuku spread it over the worst of his wounds. “How did it happen? Bringing Izuku here, I mean,” Denki rushed on as he shifted closer. Golden eyes examined Izuku eagerly while the former human busied himself tending to his mate.“You know how it happened. I felt his pull and convinced him to join me in the sea,” Katsuki explained. He shifted closer so that he could chaperone Denki’s examination. “Eijiro probably already told you the rest. My mother interrupted his change, but he still completed it.” Izuku frowned but didn’t argue. It was hardly the full story, but he knew the rest of it was theirs alone. Katsuki had warned him to be careful of how much he shared. Sirens were violently protective of their secrets. Katsuki hadn’t technically broken any tribal laws in his turning, but the information was still potentially dangerous.Ambiguity was their friend in this, and Katsuki didn’t trust Denki to think before he opened his mouth.“The pull… Would you tell me about it?” Denki muttered. There was an awed sort of reverence in his voice that tickled something at the back of Izuku’s mind. Maybe not all sirens were as disgusted with humans as Mitsuki made it seem. After all, there were several human items already scattered about this den.“Mind your business, dunceface,” Katsuki hissed. The sound echoed harshly in the small space. Izuku felt his fins rising with offense at the tone, but Denki didn’t acknowledge it. Instead, his curious gaze lifted to Izuku’s face again. “Did you feel it too?” Denki’s voice had a note of something in it that perplexed Izuku. It sounded more like desperation this time than enthusiasm, but he couldn’t imagine why. Why would Denki want to know what a human felt during the process? “I think I did. I felt something, but nothing as intense as what I feel now,” Izuku answered. He didn’t think there was any harm in sharing that much. He lifted his hand and brushed his fingers slowly over his chest. He felt the bond strongest there; like a comfortable weight fluttering just behind his rib cage. “We were bonded when he woke,” Katsuki explained simply. “So it wasn’t the pull you felt, but the bond itself. That's a beautiful story. I’ve never heard anything like it,” Denki sighed dreamily. His voice was full of romantic whimsy that made Izuku smile and Katsuki bristle.Devotion. Denki had never heard of such devotion.Katsuki might be vicious, but he was also a romantic. Izuku loved it. He was proud of his mate’s fierce adoration, but he knew Katsuki was bashful of it. His nervousness always presented as anger, but he couldn’t hide what he was really feeling from his mate. Still, Izuku mercifully turned the conversation for his alpha.“You have a lot of human items here. Maybe we could talk about them? What questions do you have?” Izuku offered. Just like that, the excitement was back. Denki’s chittering filled the space, and Katsuki began to calm again. For a while, Izuku answered Denki’s questions. They were mostly about how different items were made. He was especially interested in glass. Izuku was in the middle of talking about stained glass, when Denki looked up and seemed to forget himself for a moment. Golden eyes widened brilliantly as he moved forward. He reached up to cup Izuku’s face in his hands, and Katsuki rumbled a warning low in his throat. Still, Denki moved to brush Izuku’s curls back from his face to get a better look at his features. “You have such beautiful eyes. I have never seen such a color,” Denki muttered softly under his breath. He glanced over at Katsuki. “Just like the old gods. The color of life.” “I know,” Katsuki answered. His voice was so smug that Izuku could almost hear the smirk in it, but this was also the first he’d heard of a belief system. “The old gods?” Izuku questioned. He blinked at them both until Denki rushed in to answer.“The stories of the ancient past! They tell of green gods. They lived among us and led the tribes from ruin. Prosperity followed them wherever they went, and to know them was to love them. To obey them,” Denki explained with a soft smile. “I love the stories. My mother used to be a storyteller.” “Is that how you keep your history? Through stories?” Izuku questioned with a tilt of his head. “Of course!” Denki answered. “How do the humans do it?”“Through accounts of history, mostly. Written into books," Izuku explained. His eyes narrowed as he thought about it. He supposed written accounts would be harder to make under the ocean.“Written?” Denki questioned.“Drawn symbols that represent our language,” Izuku explained. “Humans cannot communicate as you do, with suggestion. Everything has a very defined meaning, and you have to speak the right sequence of unique sounds to explain what you’re trying to convey. But it also means we can write it down to be shared as an exact record for the next generation.” “Sounds exhausting,” Denki answered with a grimace.Izuku shook his head in good humor. The movement gently knocked Denki’s hands from his face. Izuku had already decided that he liked the omega. Denki seemed good natured enough, and he never hid anything he was thinking or feeling. It was easy to understand him. “It is exhausting, but it has its uses,” Izuku promised. “Sirens also have shared symbols, but only a few. We use them as important markers, usually warnings,” Katsuki explained. He drew one in the sand for Izuku to see. “This one means to avoid an area. We put them over the dens of venomous creatures or near areas with volcanic activity.” “What others are there?” Izuku asked in wonder.Katsuki was already drawing more symbols on the floor, when there was a short trill outside. All three lifted their heads to look, but someone was letting himself in before they could answer. The new siren was enormous. His frame was so large that he looked odd standing in the comparatively small doorway. Izuku couldn’t see all of him, but the scales he could see were raised with sharp edges. They had more shine than Katsukis, and they looked jagged and sharp in the light. The scales were jet black, but Izuku could see a red sheen in them, and he was sure he saw the start of a red pattern in the scales that were just out of sight. His hair was spikey like Katsuki’s, but it was a bright red. His eyes matched his hair for color. He sized Katsuki up immediately and seemed to puff up. His lips drew back in a snarl, exposing extremely large teeth. Most of the fangs Izuku had seen were thin, but these looked like they were made for tearing flesh rather than piercing it. He could see now that the other siren was injured. He wore bands of some sort of plant around his middle, but the faint scent of blood was still there. He wondered if Katsuki had a hand in that, because this siren didn’t even glance at Izuku. All of his attention was for Katsuki. It was Denki he should have worried about. The omega’s fins flared, and he released a horrible, high-pitched hiss in warning. The shrill sound of it seemed to bring the red siren back to himself. He looked over the group with apologetic eyes before turning to leave.The interaction was brief, but it left Izuku stiff with worry. “That was Eijiro,” Katsuki explained. He crowded into Izuku’s space and rubbed the length of his body along Izuku’s to soothe himself. Izuku could feel the pull on his mate’s instincts to ensure his safety. He’d been on edge before they were attacked, and now Izuku could feel his anxiety like a prickling of needles over his skin. “We should go,” Katsuki explained to Denki. “We’ve had enough trouble for today.”“One more thing…” Denki muttered. He moved closer and spoke quietly just for the two of them to hear. “You should be careful. It’s not just Katsuki’s position anymore. Our tribe is on edge. We’ve wondered for years if we’re cursed, and bringing a human in could feel like an omen if you’re looking for someone to blame.” Katsuki’s fins flared. He turned toward Denki with a murderous snarl, but Izuku held his hand and kept him closer. He butted his head under Katsuki’s chin, and the alpha took the cue to pull him in close. Izuku could feel his mate’s racing heartbeat beginning to slow again against his back.He heard the truth in what Denki was saying, but something about it struck him in a strange way. He couldn’t quite put his finger on it. He’d heard the frustration and worry in Mitsuki’s voice when she’d explained how difficult things had become for their tribe, but why wasn’t anyone focused on what had caused it? More importantly, why weren’t they adjusting? Working together to solve it?“Isn’t clinging to something that’s not working more likely to cause problems?” Izuku asked before he could stop himself. He watched as Denki’s eyes widened in surprise. Izuku can almost see him trying to make the connection, as though that question alone unlocked something new. The trip home was less eventful, but neither of them stopped watching the shifting landscape with suspicion until they were safely tucked into their den. The quiet of their home was a balm over their frayed nerves, and the pair was wrapped in one another in moments. Katsuki crooned low and deep for him so that Izuku could feel the soothing vibrations of his chest. Izuku’s fingers carefully prodded the site of Katsukis wound to make sure that the flesh had knit together well. Their tails lay in loose curls while they comforted one another. It took several minutes of gentle petting and reassurance before they were settled enough to decompress. Katsuki lay back against the sandy floor of their den, and Izuku rested on top of him while they spoke quietly about a day that had been more eventful than either of them wanted. “You can’t blame him. Eijiro, I mean,” Katsuki started. His fingers combed slowly through Izuku’s curls as he spoke. “Our instincts are still raw. I fought him to stay with you when my mother visited, and we’d never fought before. The two of us have always been… Close.”Izuku watched him curiously. “Your instincts… You don’t have complete control of them do you? There’s a compulsion involved?”Katsuki blinked at him slowly as he considered. Their bond told Izuku exactly what he was seeing - Katsuki had never imagined it could be any other way. Humans had similar compulsions. Flight or fight came to mind, but it never went as deep as what he’d seen between Katsuki and Eijiro. Izuku wondered if his instincts would surface in the same way given time. “You’re surprised,” Katsuki noted. His eyes narrowed with a soft sort of worry. He cupped one of Izuku’s cheeks and brushed his thumb over the line of his cheekbone. “I will never harm you. There’s no instinct stronger than the one to protect a bond mate.”“I know you wouldn’t,” Izuku promised. “It’s just not the same for humans. We live different lives, so we’re less reactionary than sirens.”“‘They’ live different lives,” Katsuki corrected fondly. “You're more siren than you know.” Izuku smiled brightly at him. He hoped it was true. Even if siren life was harsh, there was an unmatched beauty to it, and, of course, Katsuki was there with him in this life. Izuku lowered his head to nuzzle his mate’s pectoral. He hoped his alpha could feel the well of affection growing in his chest.The den was silent for a moment. “I hope he forgives me.” The alpha’s voice was so quiet that Izuku could have mistaken it for a private wish, but his voice grew as he continued. “Eijiro and I have been close since we were pups. Many thought we would pair when we were older.”“Why didn’t you?” Izuku questioned. It certainly would have been easier for him. “Eijiro is a coveted stud. Reds and oranges are said to bring prized fighters, and the brighter the shade, the more deadly they’re said to be. He and I were favored by the tribe. My mother says she could see our colors even in our baby scales,” Katsuki explained.His fingers trailed down the length of Izuku’s spine, and he relaxed easily against his mate while he waited for him to continue. He had no reason to feel jealous, and he didn’t want to rush his lover’s explanation either. “We were… Never that way. I guess there are a lot of fucking reasons. But the biggest is Mina. Eijiro only ever had eyes for her, and he’ll have no one else. They’re unbonded but mates all the same,” Katsuki explained. His voice was fond, but there was also something sad in it that told Izuku the story wasn’t over. “They feel a lot of pressure to have children, because Eijiro is so prized. I hope you meet her soon. I think knowing someone who doesn’t blame her for it would be good for her.” Katsuki's chest lifted with a deep sigh. “You know our clan hasn’t had children in a long time. Their clutches never have live eggs.”Izuku released a soft, comforting coo. He could feel how much it distressed Katsuki to say so. His friends must want those pups badly, and not just for the sake of the tribe if Katsuki was heartbroken for them. “Is it always like this? With the violence and pressure and expectations?” Izuku asked. He felt Katsuki freeze for a moment under him, but then he felt the slow exhale. “Yes.” Katsuki answered simply, but there was remorse in his tone. He thought he’d doomed Izuku to this. The omega lifted his head and patted Katsuki’s chest reassuringly. “I would still choose you, Katsuki. I’m just worried,” Izuku explained. He swallowed and attempted to resettled himself. “That’s a lot of stress, especially for breeding pairs. Fear and stress can put a lot of strain on a potential pregnancy. I wonder if it’s why your tribe has had so few births.” Katsuki guided Izuku’s mouth to his and kissed him slowly. His tongue swept lazily through Izuku’s mouth, and the slow caress soothed him. Izuku let his eyes flutter shut, while Katsuki flipped them and rested protectively over his mate. “I’m sure it’s one of the reasons,” Katsuki admitted. “Generations of sirens have lived this way before us, but, sometimes, I wonder if things are worse now.”“You’re in line to lead one day, aren’t you? Maybe… This is something you could change,” Izuku mused. “If I do, it will be with you by my side,” Katsuki promised. Their noses brushed together as they traded whispers. “And, until then, I will be here to protect you. To keep you safe.” It wasn’t a promise that things would change, but it was enough. Even if life remained just like this, violent and uncertain, Izuku would learn to live with it. He’d stay by Katsuki’s side.
----- CHAPTER BREAK -----
Izuku adjusted well over the following weeks. He quickly became accustomed to hunting and swimming. His body was getting stronger and quicker. Katsuki was convinced the changes in his scales had continued, but, if anything was happening, it was too gradual for Izuku to notice. He was making up for it with speed and clever movement. His body was developing entirely new muscles, and Izuku was reveling in his newfound skills.Katsuki was less glued to his side now. Sometimes he left to hunt on his own, and, when they did swim together, he no longer guarded Izuku’s body like he might be torn from him at any moment. Instead, they raced one another. Sometimes they wrestled or played games among the sea grass. The sirens continued to watch them with open distrust and even disgust, but no one had attacked them recently. Maybe it was because Katsuki was quick to thrash anyone who got too close, but even his attacks were less vicious now. Violence was certainly more common among the sirens. Izuku was beginning to understand that life was harder here. It made Izuku think of his neighbors in the slums. Sometimes, cruelty was about survival.It was a new way of life for Izuku, who had always been more likely to ignore a slight than answer it. He planned to focus on speed over power, so that he could escape as needed. Of course, that approach only worked if he had somewhere to run to.Izuku sat dumbfounded at the entrance of their den. Katsuki was out hunting, and so he was home alone when he heard the whistling clicks that announced a presence just outside. He was a sitting duck there alone, but his visitors didn’t actually look dangerous.In front of him was the siren he knew as Eijirou. The alpha was even larger than he remembered with his long tail draped over the nearby rocks, but he also looked sheepish and nervous. The giant seemed to be trying to make himself look smaller. It was the first time Izuku had ever seen body language like it among the sirens.
His partner, who Izuku was beginning to suspect was Mina, stood proud and smiling beside him.
Where Katsuki and Eijirou had dark scales, her’s were far lighter. They made up for that with vibrancy. The entire length of her was bright pink, and even her skin had taken on some of that pigment. Her eyes were darker than Izuku had seen in other sirens, but they were uniquely lovely with pale gold irises that shimmered in the darkness.“May we come in?” The new siren asked. Her voice was so melodic that it reminded Izuku of the sweet tinkling of bells. It made him pick up and pay attention. Izuku looked between them in a weak attempt to get a read on their intentions. He didn’t think they meant him any harm. Katsuki loved them both, even if his last meeting with Eijiro hadn’t gone well. Izuku still didn’t understand the social dynamics of his new home, but he had to at least hope this was a friendly visit. “Of course! Come in,” Izuku answered. He moved out of the way to make room for the two to join him. “Thank you, Izuku! I’m Mina, and this is my mate Eijiro,” Mina introduced as she swam by. Izuku’s eyes followed her fins as she moved. They were flowy and elegant without the spines he and Katsuki shared. “I’m Izuku, but I guess you know that,” Izuku answered happily. Eijiro followed her, but more slowly. He lifted his head, looking around with an expression that was somehow hopeful and fearful all at the same time. Izuku’s smile widened. He was looking for Katsuki. “Katsuki will be home soon, if you want to wait for him,” Izuku suggested. There wasn’t much to show them around their den. Although it was becoming less sparse. Denki had shown him how he prepared certain sea grasses for weaving, and they’d even spent some time crafting together. Izuku had made his own hanging baskets, and Katsuki had carved him some shelves, but he hadn’t added anything to them yet. “We’re here to see you too. I am sorry for how we met,” Eijiro explained. His tone dripped with genuine remorse, and the worried slant of his eyes reminded Izuku of begging puppies. The alpha reached behind his head to nervously muss his own hair, and Izuku found himself charmed. “It’s alright. Katsuki explained that it was an instinctual thing. I don’t think he blames you either,” Izuku promised. He could see Eijiro relaxing as he spoke. His gaze lifted and slowly began to brighten again.“I’m glad… I’d never snapped at him like that before,” Eijiro admitted. He shifted awkwardly in place and watched the door from where he rested. Izuku got the feeling that the alpha wasn’t going to relax until he made things right with Katsuki. Meanwhile, Mina eagerly took his hand. “Do you mind if I have a look?” Mina asked as she turned over his hand in her’s. Izuku had no idea what she wanted, but he nodded his head anyway. Her nails brushed slowly on the underside of his claws. She nodded her head as she pressed her claws to his. She tapped them a few times before turning Izuku’s hand over again and repeating the process on the other side. “The rumors are all wrong. These are already hard, and look! See the red around the beds. The color is already shifting. They’ll turn black soon,” Mina explained. “I’m sure it will be the same with your scales.”Izuku turned to look doubtfully down the length of him. His scales were less sickly looking than he remembered, but they were still a pale gray. The green had certainly become visible in some places, and the color deepened whenever his pulse raced. He was trying not to get his hopes up about the hardness. The scales around his hips were just as soft as they had been when he first changed. “You know, my scales took longer to harden than most. I remember that when they did, the ones at the end of my tail hardened first, and then the ones near my belly only hardened when my coloring came in,” Mina assured. Her voice was rushed and excitable. Anyone would be drawn to it, and Izuku was no different. He was about to ask her a question when a low snarl came from the doorway. Mina instantly let go of his hand and moved away from him to appease the new arrival.Katsuki was home. Izuku released a few trilling chirps to let him know that everything was fine. His alpha entered and looked around the room; quickly taking in the scene and looking for any signs of trouble. He didn’t find any, but Eijiro didn’t even wait for him to finish his assessment before he approached. His head was bowed as he offered Katsuki his arm, and the alphas clasped hands nearly immediately. In moments, they were pressed close, their foreheads touching as they started their stilted apologizing. Mina took Izuku by the hand and led him to the other side of the den to give them some semblance of privacy. “Thank you for letting us in. Those two are very close. Unusually close for our kind,” Mina mused as she watched them. “Eijiro was heartbroken. He thought their bond might not recover, especially since bonds like theirs are so rare.” “Most would expect them to fight for standing, wouldn’t they?” Izuku guessed. It was the piece he’d never quite understood. Katsuki had said that he and Eijiro didn’t fight, but they were both considered prized alphas. How could they not be considered rivals?“Yes. They don’t fight, because they choose not to. Most of the clan considers it dirty. Partnerships like this are considered collusion among ranking members of the tribe,” Mina explained. “Collusion? But some of you have friendships. Why is it any different?” Izuku pressed.“Such bonds are usually reserved for siblings or cousins. Eijiro and Katsuki are not related in any direct way. They merely gravitated toward one another. It was encouraged when they were young, but it changed once Eijiro and I paired,” Mina explained with a soft sigh of frustration. “But many of you mate without forming pairs, don’t you?” Izuku attempted to clarify. “We have sex without becoming mates,” Mina corrected. “And most of us pair with multiple partners if we can find enough suitable prospects. The problem is that Eijiro and Katsuki do not.”Izuku shook his head. “I don’t understand the subtleties of it at all. You have some kind of ranking system, but it’s arbitrary. You approve of some connections, but which ones involve shifting criteria,” Izuku muttered to himself as he attempted to process the new information. “You’ll understand in time. Much of it is instinct driven,” Mina explained simply.Instinct. That was the piece Izuku was still missing. It was so common for Katsuki to just know certain truths when interacting with other sirens, as though the information was written in the space between them. Izuku sometimes wondered if he couldn’t tell, because he wasn’t truly a member of the tribe. “It will be worse for a while. You should be careful. Everyone’s been waiting for their chance to get to Katsuki,” Mina warned. Shimmering eyes narrowed with concern as he graze flickered back to their alphas. “He’s the strongest in his generation, and he’s heir apparent for Mitsuki’s place at the head of the council.” “... Would a few lost fights remove him from that seat?” Izuku asked curiously. “Probably, but he’ll always be a problem for anyone who wants council control. And his death would remove him completely,” Mina answered. Her tone was quiet and gentle. Izuku felt no ill will in them, but he bristled all the same.
He’d never let that happen.
“You’re not alone,” Mina added. She leaned closer and chittered soft reassurances for him. “What he and Eijiro have is precious, and I’ll help you protect it.” Eijiro and Katsuki joined them a moment later. They swam close to one another, offering the occasional, comforting brush of fins, and Izuku’s heart eased. Their circle of friends had grown.
Izuku adored Denki.
He’d suspected that he would when they first met, but he knew it in his bones now. He visited the other omega often. Sometimes they did nothing but mutter eagerly at one another. Often, Denki asked questions about the surface and about his work on the ship. Izuku crawled into Denki’s hammock while the other omega pulled a bottle off the shelf and showed it to Izuku. There was nothing but dirt in the bottle, but Denki was fascinated by the fact that it was different dirt. Full of rocks that he’d never seen under the water. Izuku grinned widely and reached over to pull his friend down with him. Denki yelped and fell over him in a loose curl. Izuku scooted over so that Denki settled more naturally next to him in the hammock. The other omega blinked up at him even as he snuggled down beside him. Izuku reached out to playfully muss his spikes, and Denki’s insecurity slowly melted away. “Are you sure this is okay?” Denki questioned as he settled his weight more evenly in the hammock. “Why wouldn't it be?” Izuku asked. He’d never had many good friends, and so moments like this weren’t common for him until he found Katsuki. There was nothing strange about it by human standards. Friends sought each other’s company, and cuddling was a natural extension of that desire for closeness.“This is something only mates do… Sometimes mothers with their pups. I haven’t been held like this since my mother passed,” Denki explained. His voice was quiet with uncertainty, but he still wrapped an arm around Izuku’s middle and settled closer. “Oh… I’m sorry. I also lost my mother recently,” Izuku muttered. He rested his head on top of Denki’s and wrapped an arm around his back. He gave the other omega a gentle squeeze. His heart constricted at the soft, mournful sound Denki released into his chest. “I miss it. Being close. And I miss her. I miss her so much,” Denki began. “She was a good dam. Always took care of me; ensured I survived. Sometimes I miss her so much I…” His shoulders began to shake, and the hand pressed to Izuku’s side squeezed tighter. Izuku sat up a little further so that he could look the other siren over. There were no tears under the ocean, but he knew now that there was crying. Only it came as a song. The mournful melody seemed to leek from Denki’s gills, and the sound of it broke Izuku’s heart. Desperate to take even a little of that pain away, Izuku pulled the other omega closer. He brushed his fingers through Denki’s hair and let him cling while he mourned. His body was curled over, and it made him look so painfully small. Izuku wanted to shield him from everything in that moment, but all he could do was remain close - to offer him the promise that he’d watch over him while he was vulnerable. Izuku wasn’t sure how much time passed while he stroked Denki’s hair, but, eventually, the song died down to a hum and slowly began to quiet. It seemed to take Denki’s energy with it. His body went limp over Izuku’s, but the hammock was strong enough to support them both even in the still water of Denki’s den. “She was an outcast too. This was her den before it was mine. She raised me alone here, and she was kind. She wore the scars it brought with a smile,” Denki explained. “They say I’m like her.”“Good. She sounds lovely,” Izuku consoled. He felt Denki startle, but Izuku’s fingers never paused in their slow stroking. He meant it. Izuku hated the way these sirens built their world around physical strength and aggression. They had the ability to communicate, to relate, to work together - they could build something so much more than this. Outrage began to spark at the back of his mind, but his thoughts were interrupted before he could explore them. “Why care for me like this? I don’t think Katsuki would like it if we tangled,” Denki questioned. He lifted his head to explore Izuku’s expression. Something entirely new in his chest twisted at the idea of exchanging comfort for sex.“That’s not what I want.” Izuku promised, even as he bristled uncomfortably. He looked away and considered carefully what he wanted to say next. How was he supposed to explain that Denki was important, while making it clear that his body had nothing to do with that equation?Izuku turned back toward the omega and watched the way his expression flickered with worry. Izuku swept his hair gently back from his face so that they could look each other in the eye. “What we have is better than sex. We have trust,” Izuku explained. “Trust?” The way Denki whispered the word made it sound like a foreign concept, and Izuku’s chest only grew tighter. He had to explain this in a way that Denki would understand. He couldn’t leave any room for doubt if he wanted to keep the bond blossoming between them. “You know me, and you know I value you as a person. You’re important to me. Family. You trust me not to hurt you. Just like I trust you not to hurt me,” Izuku explained. He swallowed nervously and settled back into the hammock. Denki automatically adjusted to him, removing any new distance instantly. “Trust. That’s it? Just like that?” “Just like that. We look out for and protect each other,” Izuku agreed. “Protect each other? Even though we’re not mates?” Denki muttered in apparent disbelief. “We may not be mated, but we are friends,” Izuku answered eagerly. He looked up at the ceiling and released a slow sigh of contentment. “I would fight for you.” Denki answered the sentiment with a slow, continuous rumbling. The sweet purr settled Izuku’s nerves and lulled him halfway to a contented dose. The way Denki relaxed into him felt right. This was the sense of community and family he’d been missing. This felt like home.