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The first time Katsuki knots him, Shouto bites him hard enough to leave marks.
Katsuki’s rough fingers are wiping the tears Shouto has yet to realize have slipped down his cheeks carefully away when he notices the little red pinpricks his canines have left behind on his bicep, almost drawing blood.
“I’m sorry,” Shouto says, and, for some ridiculous reason, finds himself only crying harder.
Katsuki should hate him, he knows that much. He’s only doing this because the rest of the class alphas can’t handle how Shouto gets during his heats, and his next best option was swallowing past his shame to ask Aizawa-sensei.
Shouto pictures it, having to stand there red-faced and humiliated and ask the first grown up who has ever cared for him without asking for anything in return to knot him through a heat because he almost wrecked his dorm, last time, and—
And that thought just has him tucking his face into Katsuki’s neck—he can’t be Bakugou even if he wanted to, right now, not when they’re like this, and isn’t that selfish of Shouto, too?—clutching uselessly at his forearms and wondering why anyone would want to hold him when he’s hurting them?
(That’s what Katsuki is doing, though. He’s holding Shouto.)
“Alpha,” he says, something between a shameful whisper and an outright sob. “Alpha, it hurts.”
And it does hurt, even with the stretch of a knot. It hurts and it hurts and it hurts, keeps sharpening with each little thump Shouto’s heart attempts—stubbornly—against his ribcage.
But Katsuki only rubs his back, big hands warm and comforting, and then, when Shouto finally pulls away on his own volition, he cups his chin and says, “Shh, it’s okay. You’re doing great. You’re such a good omega, sweetheart.”
That’s—
Warmth flutters, brand new and hopeful, inside Shouto’s chest.
“I’m not,” he says, anyway, because his body had been molded to other kinds of touch before it knew gentleness, and sometimes the truth of it feels like venom in his mouth, acrid and bubbling behind his teeth. “I hurt you. I hurt you, and I shouldn’t have, and you shouldn’t even have to be here in the first place, but because I’m useless—”
“You’re fine,” Katsuki interrupts. “And I’m here because I wanted to be. Think anyone could’ve made me do this otherwise?” He scoffs. “Don’t make me laugh, sweetheart.”
Shouto’s face is still too warm, uncomfortably tacky with the salt of his tears starting to dry up now that he’s finally stopped crying. The way Katsuki says sweetheart feels a little like rain on a summer day, though. The kind where it’s okay if you’re crying because you’re barely five years old and you scraped your knee on the pavement and your father has never loved you, because then the rain starts, and you’re not alone in it.
In the big, uncomfortable, mushy wet feeling you don’t have a name for yet, but that burns anyway.
“Really?” Shouto asks. “But when Kirishima offered to help, I almost punched him.”
Katsuki’s palm is so warm on his cheek. “Hey, princess,” he says, “don’t take this the wrong way, but you hit like a girl.”
Shouto huffs, but it mostly melts into laughter. “Would you like me better like that?” he asks. “If I was a girl?”
Katsuki stills.
Shouto doesn’t even know why he’s asking. They barely talked about it, beforehand. It was just—well, the Shouto of three days ago who was dreading the beginning of his heat and had never taken a real knot before figured Bakugou was just trying to be a good friend. Because he’s always been better at doing these things than he was at talking about them.
So. They didn’t really talk. Shouto mostly nodded. He knows he said thank you, because he remembers the red of Katsuki’s ears when he did but—well, he kind of assumed this part wouldn’t lead to even more talking.
Then again, Shouto doesn’t think Katsuki would be the type to knot his friends, so. Maybe they should talk.
“Would you?” he asks. Then, “Katsuki?”
“You wanna do this now, huh?” Katsuki asks, his hand sliding to cup the back of Shouto’s neck. “Couldn’t wait a little?”
Shouto bites at the inside of his cheek. “I’m sorry?” he says. It doesn’t feel like the right thing to say, this time around. But he says it anyway, just in case.
“Don’t fucking apologize,” Katsuki says in return, because—well, he’s good at noticing, isn’t he? “You don’t have to apologize for a single damn thing. Not to me. Not ever.”
“That’s nice to know,” Shouto says. “You’re—ah, you’re nice too.”
It’s a silly thing to say when they’re like this, maybe, but—it feels different. Katsuki should know it anyway. Because knotting Shouto was nice of him, too, yeah, but he probably wasn’t doing that bit to be nice, so. He should know it still counts. This part. (Him holding Shouto when he doesn’t really have to, even with nowhere else to go.)
“Yeah?” Katsuki asks, voice soft, and—
Shouto wants to kiss him.
It’s not new, but it’s the first time he realizes what the tightening in his stomach means, when Katsuki’s this close. Warm and twitching inside him. God.
“Yes.” Shouto nods. “Very nice. Even—even without the knot.”
“But you needed it, didn’t you?” Katsuki says. “And I wanted to help.”
“Because we’re friends?” Shouto asks.
He can do that now. He gets to make jokes. And he knows that he doesn’t need to flinch when Katsuki scowls at him. It’s barely a scowl, actually, more the token shadow of annoyance passing through without bothering to settle down anywhere remotely important in what little space there is between them.
Katsuki grips his hips. “Sure,” he says evenly, grinding his knot into Shouto. “Yeah, we’re friends, halfie.”
Shouto tilts his head to the side. “So,” he says, “you knot your friends?”
Katsuki’s mouth twitches. “Just the ones I wanna keep forever,” he says, leaning in close just to scrape his teeth over Shouto’s collarbone, tugging at the skin there until Shouto’s biting back a whimper. “That okay with you, princess?”
“Mm,” Shouto says. “That’s okay with me.”
Katsuki laughs for real, this time. “You’re not difficult, you know,” he says. “Fine with me if you wanna bite a little. Wanna a bite you a whole lot, but you don’t hear me saying sorry for it.”
“That’s different,” Shouto says. “You’re an alpha.”
And Shouto isn’t.
No, Shouto’s an omega, so the old man put him on suppressants the second he started to smell anything like his mom used to, before she had to leave, and he’d never had a real heat before he got to U.A. and then Aizawa almost punched the wall over the number of suppressants pro hero Endeavor had his precious omega son on so he wouldn’t go and ruin his perfect plans by getting slick between his thighs.
He would have liked a son like Katsuki, probably. (But maybe not, considering what happened with Touya-nii.)
“Yeah,” Katsuki says, like it’s obvious, “and I’d be real shit at it if I minded my omega biting me. C’mon, princess, it was basically a nibble.”
I almost drew blood, Shouto thinks, and doesn’t say it.
He does say something else, though. Opens his mouth and lets another aching truth slither out, raw and scaly. “I don’t like it. When I get like that. I can barely think besides how much it hurts, and most alpha scents are downright disgusting, and—and if you hadn’t been patient enough to put up with the bad parts, I would have probably—”
“But you didn’t,” Katsuki says. “You didn’t, and you’re fine, and I’m gonna take care of your heats from now on, okay? Deal?”
Just like that, Shouto feels the prickling of tears in the corners of his eyes again. He’s used to crying during his heats, but that’s usually just the frustration spilling over, his own skin not stretching quite right over his bones, the heat mounting and mounting and mounting with no real relief no matter what he does. It doesn’t matter if he bothers to fuck himself through it or just huddles into a little ball of twitchy limbs in his nest and cries about it once the anger has mostly seeped out of him.
He ends up wiping his blotchy face either way, but this—
This is different. Because Katsuki wants him for real, doesn’t he? Wants Shouto forever, for good, because he’s just stubborn enough to mean that sort of thing when he bothers to say it. And Shouto knows that.
Shouto knows Katsuki.
So.
“Deal,” he says, nodding so hard he feels silly about it. “If—if you really don’t mind.”
He doesn’t, Shouto knows. But maybe he needs to hear it one more time, just in case. Because he knew Katsuki even before he ended up pinned down under the comforting weight of him with most of his clothes still on, his heat still more of a suggestion than an actual problem, Katsuki keeping both of Shouto’s wrists pinned to the sheets in one hand, but—
Well. Some hands-on reassurance doesn’t hurt. And Katsuki’s good at that.
“Look at you,” Katsuki says. “You’re fucking perfect, what idiot would mind taking care of you, huh?”
Shouto has a lot of answers to that, all of them prickling the underside of his tongue like needles, but instead he swallows, and says, “Most alphas, probably. I hear they like their knots attached to the rest of their body.”
Katsuki scoffs. “Idiots, the lot of them,” he says. “Besides, did you really think I wasn’t gonna keep you all to myself after this?”
Shouto flushes under the weight of the look in Katsuki’s eyes. It was less embarrassing when Katsuki was calling him pretty and a thousand other too-sweet things while he kept Shouto’s thighs spread. Less revealing.
Intimacy, Shouto thinks uselessly. That’s it. The difference between just being touched and—and wanting one person to touch you until your body can’t take it anymore, hollow emptiness melting away under their hands until you don’t care about anything besides that they keep touching you just like that.
“I tried not to think about it at all,” Shouto admits. “I was—I thought you’d hate me by the end of it, honestly. That you’d see how much trouble I am and decide I’m not worth the fuss, and then I’d have to go back to spending my heats miserable and alone.”
“Hey,” Katsuki says. “Listen to me.”
He sounds so soft Shouto can’t help but pay attention. Funny, considering how fond of hurling alpha commands at him when Shouto could barely stand, let alone keep training Endeavor was. Katsuki isn’t anything like that, though. (Of course he isn’t. He wants to make sure Shouto feels good. Endeavor never cared much about what Shouto felt even when it was the ache of having to stand on a broken bone.)
“Okay,” Shouto says. “I’m listening, alpha.”
“That’s a good omega,” Katsuki says, and something inside Shouto thaws and softens and drips down his insides, warm and good. “You’re never spending another heat alone if I can help it, you hear me?”
“You should bite me,” Shouto blurts. “I mean, if—”
“Yeah,” Katsuki interrupts, looking real smug about it. “I should, huh?”
“If you want to,” Shouto says, cheeks burning.
“You already bit me,” Katsuki says, but he hardly sounds mad about it. “Only fair, right?”
And Shouto could say it doesn’t count, that his wasn’t a mating bite, that he definitely wants that from Katsuki, strings and all, even if he didn’t know that the tug in his stomach whenever Katsuki’s eyes lingered on him in the middle of class movie night was just plain old want until Katsuki was licking him between his thighs to get him ready for the stretch of a knot, but instead he nods.
(The nodding has been pretty foolproof this far.)
“Sure,” he says, smiling. “Only fair.”
…
It’s only after his heat is over and that persistent itch sated that Shouto remembers to ask.
“So,” he says, still comfortable and warm in bed next to Katsuki, drawing lines on the inside of his forearm. “That my omega thing you said before, how long were thinking about it, exactly?”
“Take a guess,” Katsuki says, and Shouto—
Shouto touches his fingers to the back of his neck, and smiles. Yeah, he could probably guess.
(But he doesn’t have to, and that’s the best part. That, and how warm Katsuki is, pressed this close.)