Chapter Text
Kirishima tries not to remember his first rut. He had thought he’d known what it’d be like; he’d been to the mandatory health classes at school, he’d read the pamphlets, he’d tried to pay attention when the doctor’s bored nurse ran through it all. It should have been easy and short, a pseudo-rut, a mockery of what he’d experience later on. A pup-rut, his moms had called it; a normal mix of hormones and emotions that meant you were growing up.
He tries not to remember what happened, and he’s made sure never to have to endure it again.
Memories pop in flashes, snaps of scenes that come to him when an overscenting Alpha moves too close, in dreams at night. He remembers how it felt; a furious anger directed at nothing and everything at the same time. He felt the indescribable urge to run and yet the thought of leaving his room was at the same time unbearable.
He remembers his mother knocking, cracking the door open to deliver… something? Food? Whatever it was, it had crashed to the floor outside seconds later as the door slammed shut in a rush of rage and teeth that had barely missed tearing his own mother’s fingers off.
They don't talk about that. So far, Kirishima hasn’t let on that he knows it happened at all.
He woke some time later to his mom’s hushed but frantic whispers. “Baby, wake up,” she’d called, her warm hand pressed against his cheek. “Where are you hurt? Where’s all this blood coming from? Eijirou, baby.”
“Mom,” he’d cried, trembling, exhausted, smearing blood across her shirt as he clung to her with tattered fingers and a mouth full of splinters.
The bed had been in ruins, the walls were covered in deep grooves as high as he could reach. He had ravaged the room like an untamed dog left alone too long; chewed the frame of his bed to pieces until his spit ran red. It wasn’t something he could explain. It wasn’t something he had remembered doing willfully.
They swore to him it’d be okay. They’d figure it out, they had promised as the doctor pulled wood from his tired teeth. But their house was small, and if he had heard their frightened whispers in the hallways after dark, they probably had heard his muffled crying, too. It hadn’t been their fault. His moms were a pair of temperate betas who had adopted him as a baby, who had minimal experience with anything more elaborate than gentle scenting. He couldn’t blame them.
It wasn’t his moms’ fault that he was like this.
The doctors didn’t think it was an issue. “Things will settle out,” they had said, “You’ll get used to how it feels.” They had called him a ‘strong young Alpha’ and had talked about hormones; had showed him charts that marked his blood results as wildly outside normal ranges, but tried to play it off as a good thing.
“He’s just a child,” his mother had snapped after one doctor had started talking too much about Omegas for her taste. Kirishima had felt her fingers squeeze around his wrist, his own face pale and wide-eyed, and knew she had been exhausted as he was. “Middle school’s tough enough. What are our options?”
Medications, mostly. Suppressants, blockers, patches and pills. The office made them sign a release after going over it all again and again. It wasn’t like they were dangerous. Scent blocking was normal, even for kids just barely presented. The use of suppressants was less so, but it wouldn’t do any harm short-term; his body would catch up later.
Much later, if Kirishima has any say about it.
Things return to normal. They replace his bed with something nicer, fix up the walls, and patch torn bits of carpet. He goes back to school wearing patches on his neck to repress the scents his body doesn’t even produce, and he swallows his pills religiously, setting alarm after alarm portioning them out weeks ahead of time.
Kirishima tries not to be too jealous when a homeroom classmate presents as an Omega a few weeks later, talking about a pup-heat weekend full of ice cream and long naps in a blanket nest under an air conditioner. He has bigger goals to focus on: an endgame that has nothing to do with sex or gender, and he studies hard and works harder and fuck, he dyes his hair, too. It’s something he can control.
Kirishima makes it into the hero course and he’s ecstatic to find himself surrounded finally by a group of peers who aren’t obsessed with secondary genders, who don’t care what somebody smells like, who don’t blink an eye at his scent patches because half of them are wearing the exact same thing.
He settles into his homeroom seat and grins.
--
It’s awesome. He loves it. The coursework is hard and their teacher accepts nothing short of perfection, but Kirishima is eager to push himself. He wants to succeed and so do his new friends; its an environment nothing like middle school and his grin on the train home each day has never felt more genuine.
There’s really only one distraction, and his name is Bakugou Katsuki.
He’s hard to read at first. Bakugou doesn’t bother to block his scent but Kirishima can’t make it out anyway; whatever he gives off is covered by the smell of smoke and burnt sugar that wafts angrily from his palms. He yells and bares his teeth, posturing violently even as he sits at his desk, ready to snap at the smallest trigger.
So, really, it isn’t Kirishima’s fault that he pegs him as another Alpha. That’s just the obvious conclusion; Bakugou demands attention and reverence better than any textbook Alpha Kirishima has ever met.
They’re a few weeks in when Kirishima, heartbeat fast and lunch forgotten, stops Bakugou on the way to the cafeteria after class.
Bakugou turns and faces him, knocking Kirishima’s hand away from the elbow where he’d been bold enough to grab him. “You want what?” he spits loudly, slinging his book bag easily over one broad shoulder.
Kirishima isn’t deterred and asks again. “Just like one pill dude; what dosage are you on?”
Bakugou stares at him, an eyebrow raised impatiently. Kirishima is adamant that he’s not going to blush, but it feels like there’s a joke here he’s not part of.
“You’re asking to borrow one of my suppressant pills,” Bakugou clarifies.
“Yeah, man. Do you have any? I left mine at home and I was supposed to take more at lunch and I-” Kirishima swallows. He’s doing his best not to panic and he shouldn’t; missing one dose won’t spike withdrawal and he’s already taking double what’s prescribed, anyway. “I just need one,” he finishes lamely.
“You’re a fucking Alpha.”
“Oh. Yeah, I am.” He probably should have led with that information, but it had taken him too long to work up the nerve to go and ask Bakugou about this in the first place. He had thought this would be an easier conversation than it was turning into; Bakugou might sneer and cuss but he of all people had to understand this wasn’t something to fuck around with, right?
Bakugou shifts his weight to his other heel, crossing both arms over his chest. He narrows his eyes. “I’m not,” he says.
“Not what?”
“Fuck off, Shitty-hair.”
Kirishima blinks. “My hair’s-” he starts, but stops quickly, struck with his mouth wide open. Oh. Oh. Oh? “Wait,” he begins again, “you’re really not an Alpha?”
“Someone tell you I was?”
“Well, no. But you-”
“If you’re about to fucking spout some dumbass rhetoric at me, I’ll kill you.” His eyes are hard and though Kirishima doesn’t fear his explosions, it’s an effort to resist stepping backwards under the weight of that gaze.
“You don’t smell like a… like anything else,” Kirishima hazards.
Bakugou frowns, the tension in his folded arms fading. “I don’t?”
Kirishima shakes his head and Bakugou’s frown deepens, his lips carving a hard line. “You mostly smell like your quirk. Smoke. And like, sweat, I guess.”
Bakugou pulls his arms away from his chest and looks down at his hands, forehead creasing. “Huh. Guess that’s probably true,” he grumbles. He seems almost surprised by the concept until he suddenly shrugs, hands falling to slot into his pockets. “Whatever. I don’t give a shit,” he snaps.
Bakugou turns away from him and it’s only Kirishima’s vibrant stupidity that makes him shift forward and ask, “Beta?”
“Fuck no,” Bakugou calls over his shoulder, and Kirishima doesn’t have to guess again.
Bakugou Katsuki, a personality more explosive than his powerful quirk, is an Omega. It’s a concept almost bizarre enough to distract Kirishima from the suppressant dose he’s still missing.
Almost. Not quite. He spends the rest of the day in a jittery haze and when he finally gets home, crunching pills in sharp teeth, he finds his notes nothing but a mess of haphazard half-sentences. Great. Kirishima digs a full bottle of suppressants from his stash underneath his bed and shoves the whole thing into his school bag, followed by an entire roll of scent patches.
Today’s mistake isn’t going to happen again.
--
And then Kamino happens.
--
The prospect of living in a dorm with his closest friends is thrilling, but the reality of it hits Kirishima later that first evening. He’s exhausted, collapsing onto his newly made bed long past a reasonable bedtime. Echoes of the past few days haunt his mind and he turns towards the wall, collecting his thoughts; his friends are okay, they haven’t been expelled, and there, some feet away, Bakugou is safe.
Kirishima breathes. He pulls one fist closed, tucking it against his chest, the feeling of Bakugou’s hand in his fading. Whatever they are, they’re friends at least, but it wasn’t until this afternoon, gently pestering Bakugou while he tries to unpack, that he finally knew this for sure.
He went to bed hours ago, but Kirishima can hear Bakugou awake in his room. His footsteps pace back and forth and muffled words echo through the wall. Kirishima gets it. He’s surrounded by his things from home but this isn’t his room. It smells wrong, it feels wrong, and an itch burns through his chest as he tries to fall asleep. Exhaustion finally beats instinct in the early hours of the morning, and Kirishima sleeps.
Each day grows a little easier, each night he falls asleep a little quicker. He refuses to wash his sheets for now, unwilling to sacrifice the comfort of his own scent. Kirishima learns to grow comfortable in the dorms again, and learns to love it.
Bakugou doesn’t.
Kirishima can still hear him most nights, pacing and talking to himself. Mumbled cursing and muted thumps lure Kirishima to sleep sometimes, but tonight it’s too much. Tonight his heartbeat pounds in his ears as he listens to the noises behind the wall. He wants to reach under his mattress and chew another pill but… but he’s…
They had called him to stay after class that afternoon. Aizawa had calmly shepherded him into a quiet room where Hound Dog and Recovery Girl had already been waiting for him- and Kirishima knew. He had paused in the doorway, breath catching, wondering for an irrational second if he could just turn and run.
Aizawa had gently steered him into a seat and they proceeded to tell him what he already knows: he’s taking too many suppressants.
His fear overwhelmed him and they could see it. “We don’t want you to stop all at once,” Recovery Girl said, her hands folded in her lap, legs swinging from the edge of the couch. “But you need to learn how to understand and control yourself without them. We and your parents feel that this is the best time and environment to start.”
“My- my moms?” he had asked, brain working only at half-speeds.
“Of course,” she answered. “We always want the parents involved in all decisions like this.”
Kirishima had sat in silence for a long time, his hands clasped tightly over his knees. He looked up towards Aizawa, who gave him a short nod. Hound Dog simply watched, leaning over the back of the couch above Recovery Girl. He had a textbook’s worth of pamphlets in one hand, and Kirishima could read the cheesy titles of some of them from where he sat: “Your Alpha and You”, “Scenting for Pups”, and other terrifying concepts.
“I don’t want to rut,” Kirishima had insisted, licking his lips nervously. “I won’t. I won’t do it.”
He expected them to argue. He’ll have to eventually, he knows this, but he can’t… not right now. Not while he’s still trying to learn math and english and how to be brave.
Recovery Girl nodded, and Kirishima breathed again. “We’ll go very slow. You’ve missed most of your development periods, and we don’t want to hit you all at once.”
“What do I need to do?” he asked quietly. He could argue, maybe. Could they force this on him? Would they? But they’re… they aren’t wrong. He needed to figure this out and maybe this is the best place for it, surrounded by friends and teachers.
So they had come up with a plan.
It sounded easy at the time; no more scent blockers and cut the suppressants down to the standard dosage. It shouldn’t change anything, in theory. With good progress they would start cutting it down further.
But now he’s lying awake listening to his own heartbeat pulse in his throat. He wants desperately to take another pill. Two more. Whatever it takes to calm his heart down. And he could; they are there on his table. It’s stupid, because it isn’t anything but his own anxiety spiking his pulse and keeping him awake. Nothing’s changed. He doesn’t feel any different after taking only one pill before bed. It’s just the memory of what was and the thought of what could be- he can’t focus on the present.
He’s stronger than this. He has to be stronger. He has to-
Another thump from across the wall splits his thoughts and he sits up, throwing the blanket away from his legs. Kirishima’s never asked what Bakugou does over there for hours every night, but right now he has to find out. He needs to, because otherwise he’s going to have to admit that he can’t go a single day without overdosing his medication. (They wouldn’t have to know, though, would they. He could just-)
Kirishima throws himself out of bed and out of the room without finishing that thought. The hallway is cold and empty and the floor is awkward beneath his bare feet. He hears a muffled ‘fuck’ from Bakugou’s door just before he knocks, and then waits in silence.
“What?” Bakugou growls through the wood.
“It’s me.”
“So?”
“Let me in.”
The handle shifts and after a pause Bakugou opens the door. He’s dressed in his usual dark sleepwear, hair a fluffed mess. “What?”
“I can’t sleep either,” Kirishima says.
Bakugou eyes him, his gaze flickering up and down the hall before settling on Kirishima’s face. Finally he relents and steps away from the door, leaving it cracked open as an unspoken invitation. Kirishima takes it for what it is and pushes through, letting it close behind him.
The room is a disaster.
He remembers setting this up with Bakugou a week ago. He had mostly sat on the edge of the bed and watched; Bakugou had a specific place for every single thing and Kirishima quickly gave up on trying to help him out. It’d been neat and tidy and it had looked absolutely nothing like this.
There’s stuff everywhere. Clothes, pillows. Blankets pile on and around the bed. His school books are stacked neatly on the desk but they’re the only semblance of order in the room.
Kirishima steps forward, trying to take it all in. “What are you doing?”
Bakugou picks a pillow up from the floor and presses it against his chest. He stares at the unmade bed, face twisting into an ugly grimace. “I can’t fucking get it right,” he grumbles darkly.
Kirishima knows what Bakugou smells like by now. He’s spent enough time with him; studying, eating, training. He knows the difference between smoke and sugar and the scent hidden beneath it: it’s sharp, kind of acrid but more like spice. Smells like cinnamon, like it’d burn your tongue if you really opened your mouth and inhaled. He’d said that to Kaminari once, “Bakugou smells like cinnamon,” and Kaminari had snorted and said he was more than happy not to find out for himself.
Kirishima has smelled Bakugou before, but it’s never been like this. The room is clouded with something burnt and it’s not the sweetness of nitroglycerin. It makes him want to cover his nose and it’s an effort to resist. He kicks a shirt away from his feet and when Bakugou’s eyes snap towards it, he realizes what’s going on.
Kirishima blinks. “Are you nesting?”
“I’m making one, fuck,” Bakugou curses, slamming the pillow back onto the bed. “Stupid- Fucking- Blankets-” he hisses, tossing fabric with each quick pause.
“Why?” Kirishima tries to stand still. He’s never seen a nest but he knows the concept and he’s read the rules: don’t touch them, don’t mess with them, nothing without explicit permission. The anxious scenting in the air is curdling his stomach and he’s at a loss, stuck just watching Bakugou continue to dig through every piece of fabric he owns. “Is this a heat thing?” Kirishima ventures.
It stops Bakugou short and he turns, dark shirt in one hand. His stare is incredulous, shocked out of his undefined anger by the question. “Oh yeah,” he snorts, and it’s not quite a laugh but feels close. “I’m just having a fucking heat in the shitty dorms.”
Kirishima doesn’t ask him if he’s serious, but the expression must be clear on his face.
Bakugou rolls his eyes. “No, you scentless dumbfuck. I’m just trying to get fucking comfortable.” He brings the shirt to his face, breathes, and then tosses it onto the bed.
“It’s harder, being in the dorms,” Kirishima comments. Must be even worse for Bakugou, after Kamino.
“You’ve no fucking idea what it’s like, Shitty-hair,” Bakugou snaps. He pushes the pillow closer to the wall and though the whole thing still looks like an unorganized mess to Kirishima, Bakugou’s expression softens slightly.
“I do! I get it, kind of!” Kirishima insists, defending himself. “I can still barely sleep here. It’s not my space and it smells weird,” he argues.
Bakugou grunts, which Kirishima takes to mean he accepts that. “Whatever.” He turns slowly in place, eyeing the fabrics still criss-crossing the floor, his frown deep. His gaze falls on the shirt at Kirishima’s feet and then rises. “Give me your shirt,” he demands, palm stretched forward.
Kirishima’s fingers fist into the cotton over his stomach. “This one?”
Bakugou nods once and snaps his fingers, rushing him.
“Uh.” Kirishima hesitates but can’t come up with a good reason not to obey. He lifts his tank-top over his head. “It doesn’t- I don’t really have a scent, though.”
“You have a scent, dumbass, it’s just not the right one. You can’t smell like nothing.” Bakugou grabs the shirt and Kirishima is forced to watch, eyes wide, as he leans into it and inhales. “Ugh,” he complains. His eyes flash over Kirishima once and then towards the bed, his nest. “It’ll work,” he says, laying it out over the pillow.
Kirishima stares. “You’re just gonna-” There’s no way he’s not blushing; his whole body feels hot. He barely registers the acrid smell in the room dissipating slowly. “It’s okay to do that?”
“Who gives a fuck?” Bakugou carefully climbs into his bed, taking care not to disturb the visibly random assortment of blankets and pillows and clothes. He settles himself in, and though Kirishima’s relieved that Bakugou doesn’t lay right on his shirt, he doesn’t know what to make of it when Bakugou reaches his hands out, dragging it closer. “I’m fucking exhausted and I’ve got shit to do,” Bakugou snaps under Kirishimas stare. He turns his face away and pulls a throw blanket over his legs.
He should leave, but Kirishima’s always been too nosy and pushy for his own good. “Is this what you’re doing every night? Do you have to keep redoing it?”
Bakugou doesn’t respond for a while, but his eyes are still open so Kirishima knows he’s not asleep. He pulls in a deep breath before answering, letting it out slowly. Kirishima watches his chest rise and fall. “I don’t have the energy to explain this shit to you,” he mutters finally, but there isn’t much heat to it.
And really, it’s fair. Kirishima’s an Alpha but only technically. He thinks he understands on a basic level; how do you adjust to a new home after the kind of trauma he’d endured? How do you go back to school and pretend shit’s all normal? There’s nuances to nesting that Kirishima will never understand, suppressants or not. He barely knows why he feels uncomfortable in this place at night.
He wants to understand, though.
“They’re taking me off suppressants,” Kirishima announces, and it takes a moment for him to register what he’d said, shocked by his own voice. Here in the dark, tired, he suddenly felt that it was important Bakugou knows this- but maybe he just needs to talk about it.
Bakugou shifts and turns towards Kirishima. “Good,” he says. “That shit’s stupid.”
“It’s- but I-”
“How can you be the best of yourself if you cut half of it away?” Bakugou continues, ignoring Kirishima’s stuttering. “You think you’re gonna be a hero if you can’t even deal with your own biology?” His words are calm and firm, said with a bitter certainty.
Kirishima struggles to swallow. “Maybe I can’t,” he chokes. He wants to turn around and leave, run from this hard truth but he can’t- he’s struck by Bakugou’s half-lidded crimson eyes.
“You’re strong, Kirishima,” Bakugou continues. His fingers flex over Kirishima’s gifted shirt. “I bet you’re a real fuckin’ strong Alpha. Figure your shit out.”
It should be bizarre, right? That he’d need to hear this lecture from an Omega? Okay, Kirishima was the last to preach stereotypes, but-
He’d heard similar from his parents, the doctors, from Recovery Girl and Aizawa, but they’d all been so easy to dismiss. They don’t understand. How could they? Hound Dog is an Alpha but he isn’t an Alpha like Kirishima is. So why is it that it’s an Omega’s words that hit him hardest? That repeat in his skull like a ricocheting bullet?
Bakugou’s in a league of his own when it comes to strength and power and ferocity but Kirishima knows that’s not why his words hit home. It’s because Bakugou’s an Omega that he trusts him in this- because not once has Bakugou ever been ashamed of it, or acted like it was a hassle, or cared that half the population still couldn’t see them as entirely equal. He’d gone through a heat last month without preamble; simply missed a few days of class before the weekend and came back Monday having listened to the recorded lectures and with homework done like everybody else.
Bakugou sits half-buried in a nest he forces himself to rebuild over and over every night and still tells Kirishima to quit the suppressants.
“I don’t know what you’re still standing there for,” Bakugou snaps. “I’m not letting you in my nest.”
Kirishima isn’t sure how long he’s been standing there for. His nails beat crescent lines into his palms and his heart threatens to burst from his chest. He’s having the kind of revelation you only have in the middle of the night and for the first time in his life he wishes he could scent properly- he could express his sudden overwhelming determination without having to come up with words and Bakugou would understand.
“Dude!” he explains, finding his voice. He’s too loud for the hour and catches himself, but he still grins. “I’m gonna do it! Not- no, I don’t wanna get in your nest, not- not that,” he rambles, smile faltering for just a second before he continues, “I’m gonna figure it out. I’m gonna quit the suppressants!”
“Fuckin’ great, Shitty-hair,” Bakugou grumbles, turning his head back into the blankets.
Kirishima’s on a roll. He knocks his fists together over his chest. “I’ll be the best Alpha and then I’ll- I’ll get you a shirt with my actual scent on it! Properly!” he announces.
“You’re fuckin’ batshit,” Bakugou answers. He slides one palm to cover his mouth and Kirishima thinks he hears what might be a laugh, but Bakugou plays it off as a clipped yawn. “Get out of my room,” he orders, settling deeper into the confines of his nest.
“Yeah, dude, yeah.” Kirishima turns to go, his hand on the door handle. “Goodnight, Bakugou,” he calls over his shoulder.
“Fuck off,” Bakugou answers.
Kirishima still grins, and when he finally falls asleep later, it’s with an air of excitement. In the morning he’ll be struck by a sea of reservations and worries, but right now he’s confident. He’s going to be the best fucking Alpha hero anybody has ever seen.