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Damn pheromones.
Katsuki is very aware that Izuku has a nearly encyclopedic understanding of him and all his quirks, both explosive and emotional (and sometimes at the same time.)
But for years, he’s been grateful that it is only nearly; he’s lucky that Izuku can’t sense his pheromones, otherwise it would reveal something too… revealing.
(How was he supposed to know that the constant outflow of emotion could actually backfire? They don’t cover that in omega classes.)
***
Perhaps the worst part of it all is that Katsuki wasn’t even the first person to be aware of it. Throughout their whole lives, he and Izuku have orbited each other, leaving their marks on their bodies, for better or for worse. It had felt normal; correct, even. He didn’t question it.
Maybe he should have, though, in order to avoid this latest little indignity.
Because a few years after they graduated, at one of those bar nights that lasted long after the trains stopped running, with Ochako nodding off against Kirishima’s shoulder and Iida valiantly attempting to pretend he can stay awake, fucking Half-and-half cracked the damn thing wide open with all the grace of a blunt knife.
“Why didn’t you tell me you were courting Midoriya?” Todoroki asked. He’d just sat back down, and had the nerve to have a little hint of curiosity in his voice as though he’d never considered the possibility before.
“What are you talking about?” Katsuki spluttered. “And don’t say shit like that out loud.”
Todoroki looked pointedly at their friends — all immersed in their own conversations, blissfully unaware of whatever nonsense he’d decided to spout — before turning back to him. “I just think it’s strange that my best friend would keep something like this from me.”
“We’re not friends,” Katsuki spit back out of habit, before catching the little hint of mirth on Todoriki’s face, and the oddly soft scent of anise that always emerged when he was joking around. “Oh, piss off. I don’t know what you’re talking about.”
Katsuki took a pull of his drink, but frowned when he realized he’d drained his highball already.. Those words — courting Midoriya — felt so unfair; it’s impossible, after all.
“Really? But he smells so much like you, I just thought…” Todoroki frowned, eyebrows scrunched. “And you’re always –”
“Stop cutting yourself off and spit it out.”
“You’re always around him? And he smelled like you, even over the smoke.”
Katsuki tensed.
Midoriya might have a bad habit of smoking when he’s stressed, but Katsuki’s is definitely worse.
“I’m not courting him,” Katsuki muttered, weakly, before rising to get another. He wasn’t running away from this conversation. Call it a tactical retreat, call it self-preservation, but he wasn’t cowering away from reality.
Because it couldn’t be real.
An Omega couldn’t court a Beta. It was impossible.
***
Todoroki’s stupid observation made a home in his head, completely against his will.
Because the more he thought about it, the more he could — and you would never catch him telling Todoroki this — understand why he’d made that assumption.
Alongside the traditional courting gifts that Alphas gave to their omegas — soft blankets to fill their nest, trinkets to wear as tokens of affection — scenting was a key part of the whole mating dance. It was impossible to keep an in-progress courting a secret for long, because the scents of the courting couple would rub off on each other, until you were standing in front of an Alpha who smelled like sweet cream and caught a whiff of a sandalwood Omega.
But he and Izuku lived out of each other’s pockets, even now; what was a token if not a dog-eared All Might card? What was courting if not knowing someone else, the way Izuku knew him?
It was easy to slip into the habit of it. Of letting Izuku hand him blankets from their shared storage closet when his heat inched closer, marked on their wall calendar. Of nudging Izuku’s thigh with his knee when they all shoved into an izakaya booth far too small to contain the bulk of them as heroes.
They lived together; was it any fault of Katsuki’s that he started to think of home as Theirs, with all the intention of a capital T?
Perhaps it was.
Because Izuku didn’t seem to notice any of it. He brought food to Katsuki during his heats as though it was just something you did to be nice. And when he leaned back into Katsuki — a move that would rub his scent off on him if Izuku were an Alpha — it was only to look at an article on his phone or to silently signal him while they were on duty.
He was a good person. A good Beta. A best friend. And Katsuki should have just swallowed it down, taken the crumbs of comfort he could get from Izuku’s behavior, but instead —
“Kacchan, look!” Izuku said, throwing an arm around Katsuki and pulling him close so he could read the latest breakdown on Mirko’s fighting style. “I don’t think I agree with the article’s premise, but I can definitely see where they’re coming from…”
And sure. Katsuki would have an answer, eventually, but for a moment he let his eyes flutter shut, inhaling the scent of stale tobacco that hovered around Izuku after a smoke break on the balcony. Eyes closed, he could pretend that Izuku wasn’t just a Beta; he wrapped his own scent around him, enveloping him in his sweet caramel, pushing it out and out and out until he couldn’t pretend anymore.
Izuku’s scent wasn’t as alive as his own was, the smoke fading, inert. It didn’t answer his scent, wasn’t responsive. Once he’d given all he could, there was nothing left, and so he sighed, opened his eyes.
“Just say you think they’re full of shit, Izuku,” Katsuki said, leaning into Izuku’s touch.
He’d take what he can get, lest he ruin what they’ve built together.
***
Katsuki was used to wanting Izuku. He was also used to pushing past pain, to forcing a breakthrough, to making something out of his body and his quirk, that he didn’t notice the moment wanting tipped over into something dangerous, until it was too late.
“Fuck.” He stopped still in the city streets. Suddenly feeling lightheaded, he placed a hand on a random wall to steady himself, stumbling on the sidewalk. What was happening? No one unaccounted for had arrived on the scene of the quirk accident they were triaging, so there was no threat that could have caused this. And honestly, he had felt something wrong with his body all day, since he woke up on their couch neatly tucked in with his favorite blanket from his nest, his last memory before falling asleep leaning against Izuku’s shoulder while they watched an old Godzilla movie.
Ever since, his body had crackled with too much energy and electricity, the sweet caramel of his scent nearly burnt, and he felt so damn antsy.
“Dynamight?” Izuku asked over comms, a note of worry in his voice. “Are you okay?”
He was the epitome of a professional while on the clock, and normally Katsuki was too — mostly — but the honest note of concern put him over the edge.
Of course Izuku was the first to notice something had gone wrong; of course he was reaching out. He’s a good hero; that’s all.
Katsuki’s stomach twisted into knots. He opened his mouth to answer, but his throat was too dry to make words come out.
He was a good hero; he’d spent the entire accident far from Katsuki, helping out some of the victims while Katsuki was still trying to subdue the target. He kept catching glimpses of him holding someone close or soothing them, and each time he bit his lip and turned away to block out the image, and the sense that Izuku should be next to him.
When you were courting, you weren’t supposed to be that far apart, right?
In the weeks since Todoroki had clocked him, he had tried his best not to think too hard about what it all meant.
Damn near impossible, when, like a line of dominoes, the rest of their friends noticed too. The only thing keeping him from exploding with frustration over their sympathetic looks was the fact that Izuku clearly had no fucking clue about his feelings, and he’d rather keep this shut up tight than confront everyone about it.
Confront them in front of Izuku, of course, because that was the person he wanted to keep this hidden from most of all. But he was always with Izuku, which was the problem.)
And sure. Katsuki was brave enough that, if it were anyone else he’d imprinted on like a particularly explosive duckling, he’d confess his feelings and get it out of the way, but Izuku was different.
He’d always been different.
Katsuki didn’t want to lose what they had, and so he stubbornly convinced himself that it was enough, until suddenly — as if between one heartbeat and the next — he felt his body grow cold, like he’d been dropped into an ice bath. But Todoroki was nowhere near him, and the bright summer sun was blazing overhead.
“Dynamight?” Izuku again, and the concern made him ache.
The feeling was just as overwhelming as his heats were, but instead of arousal and warmth, he’d become filled with despair and cold, shooting up to his head and making him grab at his mask, his skull, his temple, just to tamp down the pain. He had no idea how much time had passed, could barely hear the frenzied worry over their comms.
Nearly went numb until he felt a warm hand on his back, almost burning, and smelled his own scent mirrored back at him. Beacon in a storm, he latched onto it, dizzy from the ache, and that was the last straw. Because, in the eye of the storm clarity, he had half a moment to realize that the caramel wasn’t coming from him, that it was mixed with smoke and familiar sweat. His scent was inert, like he’d given it all away.
He had half a moment more to hear an aborted “Kacchan?” before everything went dark.
***
Katsuki woke up in a hospital bed. This wasn’t uncommon for him or other heroes, but normally they were brought down by a villain or a natural disaster, and not their body and pheromones rebelling.
He still felt cold, but it was much more manageable. Not overwhelming like his heats usually were, and nothing like how he’d felt out on the field. His room was empty but blissfully private, and the dusk in the window told him it had only been a few hours since he’d passed out.
Katsuki was smart. He didn’t need a doctor to tell him what he’d started to realize as he sat upright in his bed, gripping the gown of his robes and absent mindedly exploding away the sweat, but it certainly helped fill in the blanks..
Courting a Beta like this, where his pheromones and feelings would be rendered inert and unreciprocated, was a disaster for more than just his mental health.
“Whatever,” he grumbled. “Just tell me what prescription I need to take to cure this.”
The doctor leveled him with a look; she was older, intense, and Katsuki got the feeling that she’d been through this kind of thing with a hundred other stubborn Alphas and Omegas before Katsuki, and that he wouldn’t be the last.
“There’s no medicine you can take, kid,” she said, scribbling something down on her chart — no doubt marking him down as a category 5 case of head in sand from the way he gritted his teeth. “You either have to confess, or get over your feelings. Pick your poison.”
“Is that really how a doctor’s supposed to speak to their patient?”
“No. But it’s the only way I think you’ll listen.”
***
To be fair. He did listen.
He just. Ignored her recommendation. Doctor’s orders didn’t a law make, after all.
But he repeated those words in his head like a mantra over the next few days, especially when he gets pulled off the duty roster and Izuku babies him at their apartment, wrapping him in blankets and bringing him tea and hovering behind him while he cooks because there will always be something he does not trust Izuku to do.
“Can you stop mother-henning me?” he snapped, once, regretting it when Izuku listened and gave him space. He felt cold and empty because of it, dangerously close to how he felt when he passed out, and he was so grateful when Izuku returns with konbini snacks and an old DVD of their favorite All Might specials to watch from the video store down the street that somehow was still in business despite the lack of customers that he could practically watch his scent amble over to Izuku, sheared away from him.
“Only once you tell me you’re alright,” Izuku replied with a smile, “and I believe it,” he added, as if he sensed that Katsuki might fudge the truth, a little.
He was feeling better, just with Izuku being there, after all, but it did nothing for his symptoms. As they wrapped a (shared) blanket around their bodies, the cold returned like a reminder of the havoc he was wreaking on himself, but Izuku didn’t seem to notice.
Small mercies.
And the hovering didn’t stop when Katsuki returned to active duty. His first shift back was light: a daytime patrol and some school visits, and Izuku bullied Todoroki into switching partners so they could work together.
“It’s not bullying, Kacchan. I just asked and Shouto agreed!” Izuku looked like very picture of innocence, but he wasn’t being the menace, for once.
“And I’m sure you asked very nicely, Deku,” Katsuki rasped out, narrowing his eyes at Todoroki’s smug expression over Izuku’s shoulder. “But that doesn’t mean it wasn’t bullying.”
It was nice, though, being side by side with Izuku while they’re working, bantering and showing off for kids, helping out with minor quirk accidents while out on patrol. There were no big surprises, but it was just good to be working again.
He’d been going stir crazy, a little, even though being in his own private bubble with Izuku felt too nice.
Calm before the storm, though. In the evening, when all the straggling members of their friends and cohort, the ones who aren’t abroad or on deep cover missions or on duty, convened to commemorate his return to the field, he could feel that brush of cold come over him again.
“I always get the sense that they just want an excuse to celebrate when they plan these hangs,” Izuku murmured in Katsuku’s ear, making him shiver from accidental delight and pain. This close, it felt like Katsuki was waiting for a scenting that would never come; according to what he’s read — studied only in the dead of night once he was sure Izuku was sleeping, before deleting his browser history just in case — Alphas and Omegas can court and date Betas; they just need to make sure their feelings are reciprocated. The silent pheromone language wasn’t enough here. The love needed to be loud.
It was a little more effort than a standard Alpha/Omega bond, but Katsuki was never one to shy away from putting in work; no stranger to being loud. He just…
He didn’t know what would happen if things didn’t go according to plan; if he could handle it, or if it would feel like a rejected mating. If he would lose the peace and life he’s built.
“I just wish they’d choose to celebrate somewhere quieter,” Katsuki muttered back, making his life harder by soaking up Izuku’s warmth and presence, and ignoring the way all of their friends seem to look at him with pity when they take a break from inane drinking games or making Todoroki cool down their beer.
“Wanna go outside?” Izuku offered, and it was considerate; proof he knew Katsuki, who nodded because yes, he wanted fresh air, wants to be with Izuku, wants —
Izuku lights up one of his damned cigarettes, shrugging bashfully at Katsuki who just rolls his eyes. They all have their vices; Katsuki’s just happens to be Izuku. And at least he doesn’t smoke the cheap shit, so the tobacco that starts to cloak him despite all of Izuku’s efforts at making sure he’s downwind doesn’t smell too bad.
It’s almost pleasant. He imagines it seeping into his skin, becoming part of him; his caramel and Izuku’s smoke merging like a French pastry chef on break, chainsmoking before going back to his croquembouche.
It makes him feel oddly warm; warmer than even the soft summer breeze had any right to make him feel, and when he turns to look at Izuku, he’s letting the glowing ash drop to the ground, cigarette frozen in his hand.
“Izuku, I —” Katsuku tries to say, before Izuku breaks in.
“Kacchan, you scared me, you know?” he saud it casually, like he’s practiced this. Izuku blinked up at the stars and the city lights and sighs. “I mean, you always scare me, but this was worse. I didn’t know what happened to you.”
“I got sick,” Katsuki said, which wasn’t untrue.
“No, I mean…” Frustrated, Izuku dropped the cigarette, grinding it under his ankle. “Normally, I get it. Every variable, every calculated risk. I know what you’re going to do out in the field, and even though you always find a way to surprise me when you break past your limits, you don’t scare me like the other day. It was unaccounted for. Impossible to predict. An unknown variable.”
Izuku’s skin gets more freckled in the summer, the dots of green make him look otherworldly as he reaches towards him, closer, and closer, until —
“I don’t want you to get hurt like that, Kacchan,” he said, hugging him way too tight with his face buried in his neck. “I don’t want you to hurt in a way that I can’t understand. What happened out there?”
Maybe it’s because he couldn’t see Izuku’s face. Perhaps it was his hands gripping at the hem of his shirt, or the scent of tobacco swirling around them mixed with sweat, familiar and comforting and all too Izuku that Katsuki starts to feel a little bubble of hope in his chest.
“It’s ‘cause I like you, dumbass,” he said, airily. “How come you couldn’t predict that?”