Chapter Text
Everything is quiet, save for the sea wind and the gentle push and pull of ocean waves. Not even the sea birds are singing today because Kacchan is singing—and when Kacchan sings, the whole world stops to listen. He’s perfect and handsome and Izuku would do anything to prove himself to him. If only he had anything to offer. Unfortunately, when Izuku sings, the whole world is horrified. He’s never quite on key, never quite in tempo, and no amount of practice or lessons have made him any better. That’s why everyone calls him—
“Deku, shut the fuck up! I’m working.”
It’s a wonder that Kacchan’s voice can be all at once musical and soft, but guttural and grating when he speaks to Izuku. Deku means useless. A siren who can’t sing—and is fascinated by humans—is the epitome of uselessness. It might hurt his feelings if he didn’t so wholeheartedly believe it.
Izuku is, put simply, an immense disappointment. He’s technically a prince, groomed since birth to lead in some sort of capacity, but princes are supposed to be desirable, handsome, and talented. Princes are more like Kacchan, and Izuku is just… himself.
“Kacchan, your voice is so wonderful. I could listen to you sing all day, every day.” He doesn’t mean to say it out loud, but he does. No matter how truthful it is, he still regrets showering him with his praise. Kacchan hates it.
Kacchan hates everything about Izuku.
“Fuck off. I’m busy.”
“Oh, is there a ship?” Izuku asks, his head breaching just a bit higher over the waves to look at the horizon. He sees nothing, but that doesn’t mean they aren’t out there. On top of his shitty voice, his sonar is also subpar. He should be able to feel the ship’s presence, but there’s nothing. Nothing but Kacchan, lazing on the outcropping of rocks at the edge of the island shoreline. His orange tail swishes in time with the crashing waves, pristine scales glistening in the mid-day sun.
“I swear to fucking Poseidon, if you fuck up this catch for me, I’ll kill you. I don’t care what Yagi says.” Kacchan levels him with a serious glare—the kind of glare that sends schools of fish darting away in the other direction, the kind that bleaches coral with the sheer heat of his disdain. Izuku reddens.
“I would never,” he mumbles, submerging his face halfway, so most of the sentence tapers off into bubbles, in an attempt to bury his blatant lie. He hopes Kacchan won’t call him out on it. Izuku would, he has, and he almost certainly will again. He can’t help it! He’s never felt fully right among the other sirens, his royal status be damned. At least with humans, he’s special. Most of the time they try to kill him, but if his friendship with Kacchan—honestly, a generous term for their tentative, somewhat hostile existence with one another—has taught him anything, it’s that friendship is nothing without the threat of bodily harm. It keeps things interesting, to say the least.
“Go home, Deku. You’re useless above sea level.”
At least he’s generous enough not to say that he’s just as useless below sea level, as well. Izuku pouts, but he obeys. He submerges himself, but lingers long enough to hear Kacchan’s song start up again. He sighs, bubbles billowing from his mouth—Izuku imagines they’re shaped like little, shattering hearts—and heads home.
“Sulking is unbecoming of the future king,” Eri intones. She’s working on her letters, silver hair fanning around her with the soft, ever present current. It shines lustrously like abalone shells under the sun. Izuku is the typical middle child, with an older brother and a younger sister—never quite bad, but certainly not the best (the eldest), and definitely not the most doted on (the youngest). Eri is only eight, but she’s already leaps and bounds ahead of him in everything—singing, dancing, writing, public speaking. The only thing Izuku could ever boast at being above average at is his fluency in the human tongue, but no one actually cares about what humans have to say. It’s a precaution, more than anything, to learn their language. Sometimes, he thinks he understands humans more than sirens, despite the initial language barrier.
“I’m not supposed to be a king. Mirio is.”
“Mirio abdicated. You’ll be king, so stop sulking, Izu.”
Izuku just barely manages not to roll his eyes. His brother, Mirio, is the epitome of perfection, save for the fact that he left their commune for another, smaller one in the far Eastern seas. He was the pride of the family, born and bred for kingship. He even looks like their father at his prime—blond, built, and blue-tailed. It’s too bad he fell in love with a quiet, Eastern siren, and up and left them all for the simple life. He still visits from time to time, but he’ll never take his rightful place on the throne.
“What if I abdicate? You can be queen and I’ll go off adventuring.”
“By adventuring, do you mean getting nailed to the prow of some sailor’s ship until you rot into sea foam?”
“Maybe,” he mumbles, considering it for a moment, staring at the evidence of his closest call to date. His hand is deformed, the webbing severed and scarred. He was harpooned right through the center of his right hand when he was ten. Kacchan saved him by ripping the thing out, with little care for the fact that it utterly destroyed his hand. He’s been obsessed with both humans and Kacchan ever since. At this point, it’d be far easier to capture a human’s attention than Kacchan’s. His heart hurts with an unrequited crush.
Suddenly, he’s smacked in the head with a silver tail fin. For someone so young and dainty, Eri packs a wallop.
“Ow,” he gripes, massaging the aggravated flesh of his cheek and neck. Her scales are sharp and cutting—a sign of fastidious grooming. Izuku’s scales almost thrum with the knowledge that he doesn’t take care of himself nearly as much as he should. She pouts, wiggling her way under his arm and nuzzling into him.
“Don’t you leave me, too.” She clicks at him, a sure sign of sisterly affection, short bursts of sonar washing over him, ruffling his curls. He clicks back in an attempt to be comforting, but his sonar is wonky—a weak mimicry of what it should be. He’s almost positive she can barely register it.
“I won’t. S’not like I’ve got anywhere else to go,” he says, nuzzling her hair.
Not like anyone else wants me, he thinks, hating himself for it, but believing it all the same. He knows his dad loves him, but he also knows that he doesn’t measure up in any way, and that—disappointing him—terrifies him to no end. He’s eighteen, and Toshinori is ill. Eighteen is the time for ascendency. Time to grow up and pick a mate and live his destined life as a king, but no one wants a mate who can’t sing, not even if they’re royal, and he only has eyes for one person. In only a few days time, every unmated siren will perform in front of the entirety of the colony in search of a match. Izuku will be expected to join this year, and as if the thought of singing wasn’t terrible enough, the thought of being left alone at the end of all the pageantry will surely be worse.
He’s all but forgotten his little sister, tucked under his arm still, until she clicks directly into his ear. The sound is deafening.
“Ow.”
“No more sulking, Izu. Go do something productive. I have lessons to finish,” she says haughtily, swishing away from him. He pouts, admiring her easy maturity. She should be queen, and Izuku should be somewhere else.
He takes his leave, content to float along the currents, resigned to going wherever it may lead him. He swishes along until a strong undercurrent catches him. It lazily pushes him along the seafloor, away from the safety of the grotto. He finds himself wallowing in his own melancholy. He’s directionless, idling—and the lingering fear that that’s all he’ll ever be is debilitating. He floats higher to the surface, facing skyward, eyes closed so he can feel the setting sun, it’s brightness and intensity dulled by the depth of the sea, instead of seeing it.
Sometimes, he wishes he could float through the sky as easily as he does through the water. He wishes for the horizon to melt seamlessly, blending sea and sky so that he might cross over, and find someplace new. Somewhere he fits just right.
His thoughts are interrupted when the waning light of day is blotted out completely, leaving him the slightest bit cold. He opens his eyes to find the underside of a behemoth of a ship. He smiles, knowing Kacchan may actually kill him this time. Still, he moves closer, fascinated by the wooden hull and the seafaring humans within.
Katsuki smirks at the approaching ship. The idiots onboard are drawn to his song, and soon they’ll be crashing and burning, drowning in an attempt to catch a glimpse of him.
“Dumbasses,” he mutters, before continuing his song, his eyes on the doomed vessel. They’re so close to the shallow, rocky seafloor, now. They’ll be sinking before they know it. This is what they get for treading on the sirens’ domain. He’s momentarily distracted when something crests above the water. He knows there’s only one creature ballsy enough to get that close to a ship, and he’s immediately infuriated. A glittering, green tail splashes on the surface as he dives.
“Fucking Deku!” Katsuki screeches as he bails off his rock and slithers under the surface of the water. He’s going to get himself killed, either by the humans or by Katsuki’s own webbed hands. Deku’s too fucking reckless. He’s supposed to be a king, but he’s never once acted like it. He’s got so much potential, an almost hidden grace with that inordinately muscled tail of his swishing along like nothing fazes him. Katsuki would give anything to be in his position—a future king, revered by all and wanted by everyone. He deserves to be in his position, and the idiot acts like he’s so above it, chasing after humans every chance he gets. Just because he vacillates between hating him, and being enamored by him doesn’t mean he wants the fucker dead. Katsuki clicks frantically, trying to reach Deku, but the idiot never listens when he calls to him.
He remembers, with intense chagrin, when they were younger, and Deku was this fucking close to being skewered through the chest with a harpoon. He yanked him out of the way, but he was still hurt. His deformed, broken hand haunts him, and ever since he’s been far less concerned with trailing after sailors, and far more concerned with leading them to their demise with a zeal that could only be described as hateful retribution.
He can’t fathom why Deku hasn’t learned his lesson. Katsuki has, and he’ll be damned if the one and only person he cares about is reduced to sea foam because he’s too stupid to be cautious. If there are no humans to observe, there’s nothing distracting Deku. He wants his eyes—those stupid, pretty, bright green eyes—on him, and only him.
Izuku stays close to the surface, occasionally bobbing his head above the water to listen to the bustling sailors on the ship. They’re frantic with need to find the source of that beautiful song, trying to replicate it with their own voices. None of them sing like Kacchan. Maybe that’s why Izuku feels so connected to the humans. He’d die to be with Kacchan, too. He follows alongside the ship for some time, lost in the sound of shuffling feet and the mimicry of siren song.
It tends to drive humans mad, the songs of their people. If the ship doesn’t crash first, the sailors aboard will surely kill each other in some sort of competition to be the only one to look upon the siren. The sun has set, and the stars are clear against the endless night. Izuku likes the dark. At night, the horizon melts, the water dim, the pinpricks of light in the sky reflecting off the tumbling surface of the sea. It’s hard to tell where the sky ends and the water begins. The calming dark is desecrated when the ship alights with shattering glass and a minor explosion.
Izuku stops abruptly, no longer content to float along by. Flames lick the deck of the ship. Some men scream and others continue their rendition of the song, chanting feverishly with little regard for their safety. A shadow hoists himself over the rail of the ship, obsessively repeating the song. He dives off, clearly determined to find Kacchan. He’s diving to his death, but Izuku won’t allow that. The sailor hits the water with a plunk, and Izuku wastes no time diving after him.
The human dove straight down, with little regard for whether or not he’d be able to swim back to the surface. That’s what siren songs do. They call men to the sea, make them burn with a desire that only vast oceans can quench. He writhes, choking and gasping, the last of his air bubbling out of him. Izuku hooks an arm around him, the billowing cloth of his shirt catching on the scales of his arm. It’s jarring to be so close to a human, to feel his heavy, graceless body flush against his own. He flicks his tail, charting a course for the surface, determined to keep this man alive.
Izuku drags the sailor up the beach, his tail flopping uselessly behind him as he squirms. The tide laps at them, but Izuku’s already feeling too dry. The man is passed out, but he’s breathing shallowly. Izuku is content to watch him, to observe the way his soaked shirt pastes itself to the planes of his muscled chest, to run his fingers through his bright red hair. He’s never seen a human so closely, and now he knows why he’s always craved human interaction. They’re beautiful, in an odd way. His legs are slightly off-putting—almost ugly, actually—but he supposes that’s just because he’s never seen a pair of feet up close. He pokes at one of them curiously, and the human’s response has him jumping so high he nearly retreats back to the sea. The little things on the end of his feet—almost like fingers, but stubbier, and far less useful— wiggled. Disgusting… but fascinating. He pokes a finger into his foot again out of morbid curiosity. This time, the man coughs, expelling sea water from his unevolved lungs. Izuku is frozen in shock.
The human abruptly sits up, still coughing. He wraps a large hand around Izuku’s arm, crushing the rigid fin there. Izuku hisses on principle, though the grip hardly hurts. The man quickly releases him, but he stares hard in wonder at the sight of Izuku.
It’s funny. He’s not even looking at his tail, or the patches of scales along his arms, or the small gills on his neck. He’s just staring… at him—at his plain, ordinary face.
“Are you the singer?”
Izuku is dumbfounded. This human has the same red eyes as Kacchan, beautiful and glittering like the blood moon on the water. He wants this human to like him, so he nods, desperate for approval. His answering smile breaks open, warm like the sun. Before Izuku has time to fully appreciate it, the strange, beautiful human fists his hands into damp, green curls, and pulls him into a kiss.
Katsuki searches around the sinking ship for Deku. He’s nowhere to be found on the surface, and the growing chaos of the fire, the deteriorating ship, and the suiciding sailors leave him panicking slightly. Was he caught? Will he find him with another harpoon in his body? Has he already melted into sea foam?
“Deku!” He screeches between his furious clicking. Deku never hears him, but that doesn’t mean he can’t use his sonar to find him.
“Fuck,” he mutters, as more sailors smack into the water, drifting down, down, down. He clicks again, and it’s an impatient sound. He finds him just before he hits the surface, a burly, lump of a human in his arms.
He follows him to the shore, cursing the fact that Deku is so much faster than he is, even with the dead weight of his passenger. By the time his head crests the surface of the water, Deku is locked in an embrace with the human, their mouths pressed firmly together.
There’s a pounding in Katsuki’s ears that might be his heart attempting to rip itself out of his chest. He feels a pain sharper than anger or disappointment, sharper than the harpoon that almost took Deku from him years ago, and he’s not sure exactly what it is. He’s too overwhelmed to really push it away, and he’s considering dragging himself up the beach and snatching Deku away when something else happens.
Deku’s tail loses all its luster, drying out at a breakneck pace. His scales shed rapidly and translucent skin sloughs away, carried off in the wind. Deku’s tail has entirely disintegrated into a pair of hideous, pale—though surprisingly thick— legs.
“Deku,” he bellows, horror-stricken because he’s never seen anything like this. He feels a need to simultaneously abandon him to his fate, and get on land and drag him back into the water, so that maybe they can forget about this and go home. Can Deku even swim with those things? Can he still breathe underwater?
Deku and that stupid, disgusting human break apart. It’s obvious the sailor can’t see him in the dark because he’s an unevolved idiot, but Deku’s eyes still shine in the dark, acidic green reflecting the light of the moon. He can see him. Their eyes connect just for a moment before Deku looks down at where his tail used to be. He gives a strangled yelp at his unsightly new appendages, touching them lightly, as if to clarify that what he’s seeing is real.
“Deku, get the fuck back here!”
“There are more of you?”
Izuku is momentarily distracted from his new lack of a tail by his companion. His companion who just kissed him.
“Um, I—“
“What happened to your tail?”
“Don’t know. Um, oh my. What is going on?” Izuku murmurs, more to himself than to the sailor he rescued.
“Deku, get the fuck back here!”
Izuku starts at the terror in Kacchan’s voice, his legs—he has legs, what the fuck—curling absentmindedly. He’s thankful that he can at least move them. He needs to go back. A gentle, calloused hand on his knee pulls him back to the present moment.
“You’re so beautiful.”
Izuku shivers, both because he’s cold and because he’s never been called beautiful before. He feels a strange urge to use his new, wobbly legs to follow this human wherever he may go… but that’s crazy. That’s insane.
“I—I have to go.”
“Will you come back? Will you sing to me again?”
Izuku can’t say what he wants to say, and he can’t lie, so he says nothing, mouth agape.
“I’m Eijiro. Please, say you’ll come back to me.”
“Ah, I don’t know,” he says, hedging between a desperate yes and an are you crazy?
“I’ll be here tomorrow. After the sun goes down. Will you come back?” He looks terrified at the thought of separating, and Izuku finds it endearing, his heart softening just so.
“Okay,” he whispers, because he wants to, but also because Eijiro’s grip on his shoulders is firm, and he doesn’t know if he’d let go without confirmation.
Eijiro looks at him like the sun and moon rise and set just for him. No one has ever given him so much attention, so much unbridled respect. He pushes Izuku’s wet bangs out of his eyes and kisses his forehead.
“Sing to me again. Tomorrow..”
Izuku crawls away on unsure legs, submerging himself entirely, save for his head. He looks back at the sailor, at the only person who’s ever shown him romantic affection, and finds him waving dumbly, almost trance- like, after his retreating form. He lifts a hand to wave back, but Kacchan is suddenly beside him, smacking it back down under the water with a harsh slap.
“What the fuck, Deku?” Kacchan splashes him, a webbed hand pressing into his face until his head is fully underwater. Izuku expects to breathe normally, but he finds himself choking on sea water, flailing now that his legs are off the bottom. Kacchan might actually kill him.
He seems to sense this because Izuku’s head is yanked up by his hair just as suddenly as he was submerged. Izuku coughs, expelling sea water like it’s poison so he can breathe again. He’s still flailing, still trying to make his useless legs work for him.
“Kacchan,” he says between shuddering lungfuls of air. “Don’t—don’t do that, please. I can’t breathe.”
“No fucking shit, you useless human!” Kacchan smacks him upside the head, and it actually helps center him, edging slowly away from his choking panic. “What the fuck did you do?”
“I don’t know. I mean, I saved Eijiro, and then—“ Izuku doesn’t get to finish his piss poor explanation because he can’t quite breathe again when Kacchan pulls him close in a rough, angry kiss. It’s more teeth than anything. He’s almost positive Kacchan bites him.
“Wha—?” So many people are kissing Izuku today. It’s dizzying, but also—
“Ouch! Oh, fuck!” Izuku screams when his gills tear holes in his neck, and his fins crop back up like razors sprouting on his arms. His scales are shiny and new again, cleaner than Eri’s. “Oh, I’m fixed.”
“Eijiro?” Kacchan bites out, rage turning his face a blotchy red. “You’ve got to be fucking kidding me! What a stupid, fucking name. Should’ve let the idiot drown. Fucking humans. Swear to fucking Poseidon, Deku, if you ever pull this shit again, I’ll—!”
Kacchan keeps up his tirade, but Izuku’s not listening anymore. It’s almost impossible to stop him once he works himself up, and in any other circumstance, Izuku would be attentive, hanging on his every word, but he’s having his own little crisis at the moment.
“K-Kacchan kissed me,” Izuku breathes, face dipping below the waving surface of the water. He relishes in the familiar fluttering of his gills. It’s nice to breathe again, to recognize the bodily processes he never once gave thought to before.
“The fuck were you thinking? You’re gonna get yourself killed! What would you do if I wasn’t here to change you back?”
“Wait, how did you know that would work?”
“Because I used my fucking brain! You should try it once in a while, stupid Deku!” To add insult to injury, Kacchan spits, like kissing him was so awful he had to clear away any evidence of him on his lips. Izuku feels an urge to roll his eyes. He’s completely spent—apparently, altering one’s anatomy is tiring work—and all he wants to do is forget this unfortunate little mishap, and maybe cry his eyes out when he gets a moment alone. Except…
“Eijiro wants to see me again,” he mumbles entirely to himself, looking back at the beach, and that stops Kacchan’s diatribe in its tracks.
“Don’t you fucking dare,” he grits out, murder in his eyes. “I’ll tell Yagi.”
“No!” He yanks on Kacchan’s arm with a desperate force that startles them both.
“The fuck do you mean, no? I’m not going to let you—“
“Let me? Since when do you care about anything I do?” Izuku shrieks, suddenly indignant. The last threads of his patience have snapped. This isn’t what he imagined when he spent all his time wishing for Kacchan’s attention. “Who cares if I want to… to make a new friend!”
Kacchan reels back like Izuku slapped him, eyes tight with thinly concealed rage.
“He’s human, Deku.”
“Well, clearly something about me is human, too. I had legs, Kacchan! I almost drowned just now. That’s not… normal. Maybe this is how it’s supposed to be! Maybe this is why I don’t fit in. Maybe this is why nobody likes me. I’m a freak of nature!”
Kacchan literally slaps him. Izuku holds his cheek, pouting at the leftover sting.
“Ow! What was that for?”
“For being a fucking idiot! You’re a goddamn king in waiting. Act like it.”
Izuku frowns, thinking of his family. Thinking of what he said to his sister only a few hours ago—adventure, sailors, and seafoam. When he said it, he thought he didn’t belong anywhere, but now… maybe he knows where he’s supposed to end up.
“I shouldn’t be, and you know it,” he admits. “I’m not good enough. Eijiro, though…. He likes me! A bit. I mean, he thinks I sang to him.”
Izuku’s getting lost in the idea of it all. He thinks of Eijiro and the dreamy look in his pretty eyes, the cords of muscle in his neck, the planes of his chest under his thin, soaked shirt. It wouldn’t be so bad to be cared for by someone like him. When Kacchan speaks again, he almost sounds tired, so exasperated to be listening to stupid Deku for an extended amount of time. Izuku feels like crying, but that would only make Kacchan angry again.
“Who fucking cares? You’re being stupid. Don’t do this shit again. We’re going to go back, and forget this ever happened.”
“He wants me! He was… really nice.”
“No, he wants me. What’s he gonna think when you sing to him with your shitty, terrible voice? Who would want you after that?” Kacchan’s words cut clean through him, sharp and severe. Kacchan has always been good at pinpointing his every insecurity with fine, cruel precision. He thinks of the ceremony again, how awful it’ll be to really know that no one wants him. Izuku definitely feels like crying. Instead, he does something crazy—something he never would’ve done if he hadn’t just tasted genuine approval in Eijiro’s lips. He punches Kacchan, his fist colliding with the perfect, tanned skin of his cheek. If not for the pain in his fist, he might not have believed it really happened.
“Shut up, Kacchan. Just— shut up!”
Izuku dives, ready to be done with this. There’s no point in arguing. He takes great pleasure in the fact that he’s always been faster than Kacchan. He won’t catch him—and he won’t catch him tomorrow, either, when he goes to visit Eijiro again. He won’t catch him when he’s on shore, with legs, walking away from a lonely existence underwater