Chapter Text
As a beta, Katsuki couldn't tell other people's secondary gender from their scent. Only alphas and omegas could pick up on them so the most he could do was guess. Of course he'd assume Izuku is a beta or even an omega, absolutely not once having prime alpha in mind. He's completely oblivious of it, somehow manages to stay uninformed because he never cared about genders to begin with.
It was until he started realising his feelings for Izuku that he began caring. He heard from his friends that Izuku was a late bloomer. While everyone already presented in middle school, Izuku's happened when they're already in UA and coincidentally enough, it was when he was kidnapped. He never really got the chance to know what his gender was and in no way he'd ask. He doesn't want to sound like a creep ! He decided to do what he does best and of course, it's to use his brain !
His first guess was a beta and he has a really solid reasoning for it !
The nerd almost never had a heat break. Other omegas in his class would at least have a minimum 2 days of break during their heat. He even witnessed some of them struggling with it including the boys but Izuku ? It never seems to be the case. Katsuki started making deductions on his own, wondering if Izuku's pain tolerance was just that great considering he breaks his body so often. Though it makes sense, it's unlikely because Izuku might also not have a nest, or need one. He never saw the nerd taking any pieces of clothing's from anyone. If he does, Katsuki would know because his regularly scheduled eavesdropping session would’ve picked it up but there's no indication that izuku ever did.
He became confident with his conclusion. Izuku must be a beta ! No heat, no nest, almost no reaction to scents and alphas growling during battles or around villains ! Clearly a beta !!!
He thought.
Totally was not expecting Izuku to go absolutely feral when a particularly strong villain manages to plunge him into a building. The next thing he knew the second he regained his footing was blackwhip spiralling and Izuku growling while baring his sharp fangs. The nerd was drooling as he began attacking at high speed. It was such a mess that three pro heroes had to hold him back AND struggles. Katsuki calling out to him was the only thing that manages to snap him out a little before they knocked him out unconscious.
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"I-Im sorry for the troubles i caused !!!" Izuku started apologising profusely the second he woke up, adjusting the muzzle they had put on him as if he's used to it.
"Ah don't worry ! It's rare to have prime alphas around, we understand you're protecting your mate !" The pro hero patted Izuku on his shoulder while nodding at Katsuki as well.
Huh ?
"O-oh Kacchan is not my mate.." Izuku mumbled to himself, suddenly all shy and awkward but the hero was so talkative and probably didn't even hear him.
"You two should rest, I'm sorry about the muzzle !" The man then turned his heels to Katsuki and offered him a smile.
"Your alpha is stable now so you can stay close but the muzzle has to stay on !”
Katsuki only blinked quietly at that, not sure if he should be yelling at that man for talking nonsense or to even try processing everything he just learned.
"Sorry Kacchan ! He misunderstood ! I think it's because I got a little mad that Kacchan was hurt- a-are you okay now ? Are you feeling pain ? I'm so sorry I was a little late ! I lose control a bit..did black whip reach you ? D-Did it scare you ?? I’m so so-"
"You're..an alpha ?" Katsuki's question halted Izuku's mutterings, making him tilt his head in confusion.
"Uh um yeah ? More accurately im a prime alpha..but that doesn't matter, it's the same thi-"
"Nuh uh ??? It's not the same thing at all !! You're a fucking al- prime alpha ???"
"Well yes !"
“FUCK YOU !”
Katsuki shoves the nerd away, feeling EMBARRASSED now. His analysis was way off !!! No wonder Izuku has zero reactions to other alphas ! It's not because he couldn't tell by their scents, it's because he's practically immune to them ! Regular alphas threats wouldn't even budge him. That's why even omega's scents never bothered him ! He remembered from class that prime alphas took stronger suppressants because of their animalistic tendencies, so their sense were numbed down a little. They needed a really solid trigger to go batshit.
Izuku was batshit.
"You're muzzled.." Katsuki muttered, eyeing the metal mask that has always been part of Izuku's hero suit. How come he never noticed that ? He thought the nerd just wanted to look cool or something.
"Yeah it's alright ! As long as I didn't hurt anyone.." Izuku bashfully scratches at the back of his head with that goofy grin of his. At least he looked apologetic.
"You said it was because of..me ?"
"Well uh um..it's actually an internal-"
“Cut the bullshit.”
"O-Of course it's because I don't want Kacchan to get hurt ! I was so worried that something might happen to you ! What if you're really injured ?! I couldn't possibly let anything happen to Kacchan, especially something that dangerous-" Katsuki raised a brow as the nerd began spouting out words he could barely catches anymore. He couldn't believe this crying loser is a prime alpha of all things !
"You're stupid, I'm not some fragile beta. Not an omega for you to claim either." Katsuki spat almost bitterly. He knew he'd hate this part where he had to do a reality check.
"Of course kacchan is never fragile ! You're the strongest hero I know !" Izuku frowned, his tone suddenly a lot more stern. See, Katsuki doesn't know shit about alphas scents or aura but he could feel his hair standing up when izuku stared at him so intently, as if he might eat him whole.
"..Kacchan is really important to me..beta or omega, I never cared. It's Kacchan." Izuku blubbered to himself, clenching both his fists to show determination. Katsuki could never stop him even if he wanted to, not when he looked like that. Important huh. How far ? In what way ? What does that even mea-
"Can I court you ?" Izuku suddenly blurted out, as if answering the questions in his head.
Oh. It’s like that.
"You know you can't possibly mate me right ?" Even if Katsuki wanted to so badly, he can't afford to be hopeful. As much as Izuku said he loves him and wanted him, an alpha couldn't possibly be satisfied with a beta, with someone he couldn't claim. It's only nature.
"I'm a prime alpha kacchan, I'm in control of my pheromones and desire." Izuku responded smoothly, looking as ready as ever. He reached for Katsuki's hands with his own, calloused ones. They're rough and firm, just like his words. Katsuki hated how all of his doubts slowly began to disperses when Izuku stares at him with those big eyes.
"Cocky bastard.." Katsuki found himself muttering, feeling a wave of heat rising all the way to his face. Izuku looks confident and determined, hell, he looked strong. A strong prime alpha to rely on huh. Is this how omegas feel ? This sense of security and affection ? If this is it then he might..get what they meant. It was as if the prime alpha would do anythIng for his sake.
"I..love Kacchan so much. I love you and I want to court you." The confession nearly made the beta fall on his knees but he held back, finding himself trying his hardest to act nonchalant as he shrugged.
"Y-Yeah ? That is if you can handle it."
"Don't worry ! I'll do my best ! I'll court Kacchan properly. Also if Kacchan would like to, you can spend one or two of my ruts with me and that can alter your body to become an omega and we can properly mate ! You can bear all my pups-"
HUHHHH ???