Chapter Text
Beta?
Bakugou Katsuki thinks gender is the biggest fucking bullshit in the entire world. Living in a society where people don’t have just one but two genders means that there is a whole damn bunch of expectations attached to what kind of genitalia you were born with. Katsuki thinks it’s stupid as fuck and he was very glad he didn’t have to deal with any of that.
Katsuki was happy to declare himself to be completely immune to the twists and turns of society when it came to gender — at least, for his secondary one, since Katsuki was an unpresented beta. He didn’t have to worry about scents, ruts, heats, territories, traditions, who wants to fuck who, who wants to subdue who. If people are alphas, betas or omegas barely registered in his mind since he couldn’t identify people’s secondary gender on his own by scent.
Sure, omegas tend to have those famous ‘child-bearing hips’ and alphas are generally larger, but that’s about as far as Katsuki’s ability to identify them went. Betas overall have very dull senses, and an unpresented beta was as good as scent-blind when it came to pheromones.
The alphas and omegas in his class used to brag about smelling a villain from blocks away, so one could think that Katsuki saw this as a disadvantage. However, being an alpha or an omega came with so much extra baggage that Katsuki was happy to forgo the increased sense of smell. Besides, when he presented officially as a beta his sense of smell would get slightly better.
And by every means, Katsuki was expecting to present as a beta. Though his mother is an alpha, his father is a beta; and beta is the dominant gene. Sure, Katsuki may be a late bloomer, being the only student in class 3-A to not have presented yet. but when he were to present, it’d have to be as a beta.
Being a beta meant Katsuki didn’t have to worry about missing school days because of ruts or heats; he didn’t have to worry about someone’s scent throwing him off his axis, be it because it was too enticing or too threatening; he didn’t have to waste time thinking about mates and sex. Katsuki wasn’t hindered by his instincts and libido like his everyone else, and he couldn’t be happier with that.
However, one day, things changed.
Katsuki was working at his internship paired with Kirishima as they patrolled their area when he saw a purse-snatcher pushing a woman and her pup. The weirdly-looking man threw the pair to the ground and ran away with her belongings. The heroes-in-training didn’t have to think twice before sprinting after him.
But what should have been a routine apprehension quickly became something else. Huge explosions launched Katsuki forward at unbelievable speed. Explosions that were way too big just to catch a random villain who doesn’t even seem to have a speed quirk — that should have been the first red flag.
Unfortunately, no one realized how out of the ordinary it all was. Not even Katsuki. No, his brain was completely focused on hunting down the villain. The moment Katsuki saw the woman and her small pup being pushed to the ground, it was like something snapped inside him. There was an urge to reach the villain — an apha, Katsuki’s brain provided — and make him subdue.
Using his quirk, it didn’t take long for Katsuki to leave Kirishima behind. He didn’t care about that, though. Thrill was running in Katsuki’s veins when he realized he could corner the villain in an alley just half a block away. Hands blazing, he herded the man close to the entrance then used a particularly large explosion (way too large for the busy shopping district in business hours they were in) to jump over the villain and force him inside the alley.
The purse-snatcher was even less impressive up close. His quirk seemed to be an animal-hybrid kind, some sort of rodent. The big whiskered nose sniffled the air and made him look like a scared little mouse, despite the fact the alpha was taller and larger than Katsuki.
Somehow, seeing the alpha only made Katsuki angrier. Fury ran through him like never before, hot lava burning every rational thought in his head. He wanted to tear the other man apart, teeth and nails, limb by limb. Katsuki was used to anger, but this made every previous time he thought he was angry to seem more like a slight annoyance. This was true anger. He wanted to kill that man, unmercifully and violently.
A terrifying, animalistic growl ripped through his throat as a last warning — not that Katsuki would have let the man get away from the fight after having him cornered. The mouse-man shook all over, fear oozing from every pore and giving every indication that he wouldn’t put on a fight to the hero. And still, Katsuki pounced.
At that moment, Katsuki was more animal than man. A wild beast that forgot to use his quirk, way too caught up in tearing the enemy down with his claws. The villain tried to fight back, but it was pointless. Katsuki threw him around like a rag doll.
“No! No! Please! I’ll never do it again!” the villain begged.
The smell on the alley was so strong that it was almost making Katsuki gag. Instinctively, Katsuki knew the awful stench was coming from the villain and that the only way to make it stop was to kill him. He raised his hand, ready to deliver a finishing blow on the man’s head — just to have someone grab his arm.
“Bro! Stop it! What are you doing?” Kirishima yelled at him.
That should have been another warning to tip Katsuki off that something wasn’t right. Kirishima wouldn’t stop him if he was just apprehending a villain like usual. But Katsuki was too gone to think about that.
In a mindless response, he pushed his friend away and went back to attacking the villain. More growls came from Katsuki who seemed to have gone completely non-verbal, furious that someone tried to stand between him and his target.
“BRO! STOP!” Kirishima pleaded; his hardened form chipping away at each hit from Katsuki’s fists that he intercepted.
Luckily, unlike Katsuki, Kirishima was completely cognizant. He hardened his skin as much as he could and roughly pushed Katsuki to the wall. Katsuki hit the brick wall hard enough to get disoriented for a few seconds — just enough for Kirishima to yell on his comm line.
“DYNAMIGHT WENT FERAL! I THINK HE’S IN RUT! I NEED BACK-UP NOW!”
Katsuki didn’t hear anything else, though. As soon as he shook the hit off and got back on his feet, his anger was redirected towards Kirishima — and he went in for the kill.
He doesn’t remember what happened after that.
Days after, when it was all over, Kirishima told him they fought for a few minutes, that his hardening quirk and the fact Katsuki wasn’t using his own quirk were the only things to keep him alive. Kirishima also told him no one blamed Katsuki for what happened.
Everyone said that, actually. They said there was no way of knowing, that it was a one in a million kind of case. Kids of beta parents usually are betas; there was no reason to believe Katsuki would ever present as an alpha. And alphas usually present young, from 12 to 15 years old. It was practically unheard of an alpha presenting at 17.
And yet, that’s what happened. Katsuki presented as an alpha and went straight into a rut, leaving a bloody path of violence and destruction in his wake.
***
What followed after his dramatic presentation was pain.
The doctors told him that the later in life someone presents, the harsher is their first heat or rut because of accumulated hormones or some shit like that. Katsuki’s was hell. His whole body hurt as his muscles spasmed in excruciating contortions. He felt a hunger that couldn’t be satisfied with food; his mouth was always flooded with saliva as his mating fangs grew, splitting his gum open. The only way Katsuki could find to relieve the hunger and pain in his mouth was biting down on his pillow, which ended up with crescent-shaped bloodstains.
Another thing that hurt like hell was his dick. The damn thing was harder than ever before, not only filled with blood but filling with blood. Every hour that passed made his cock grow larger, and the knot on the base grew thicker. Not that Katsuki could realize that the pain came from his genitalia changing; all he could do was grind it down the mattress, begging for a release that never came.
And as if pain and hunger were not enough, there was also anger. It thrummed on his veins, whispering all kinds of diabolic things to Katsuki’s mind. That he should claim, control, make people subdue; that he couldn’t trust his friends anymore, that he had to make everyone submit to him. Every time a doctor or nurse came to bring him food or check on him, he’d attack them for entering his territory. Katsuki had to be put under several times so he wouldn’t hurt the medical staff.
After those nightmarish days were over, all that was left was shame.
‘No one could have seen it coming’, the doctor said. Fuck it. Katsuki should have seen it. It was his fucking body. He should have realized when things began going haywire. He should have stayed back, let Kirishima handle the petty thief. He shouldn’t have attacked his friend. He shouldn’t have trashed the hospital room. He shouldn’t have terrorized the nurses.
With complete disinterest, Katsuki heard the doctor explain shit about neutralizers, suppressants, scent blockers, and all kinds of stuff he’d have to take, inject, or whatever. He was too busy hating every second of the changes that would be coming to his life to listen to it.
His mother was there too, trying to convince Katsuki to pay attention, saying that stuff was important. But the old hag knows him way too well; she knows when Katsuki isn’t ready to talk about shit. She offered a few words, ‘It’s not that bad, brat. Once you get used to it, you may even like it’, and tried convincing him to talk to her, ‘Whenever you want to talk alpha to alpha, I’m here’, but he just blew her off.
Still, life goes on. And now Katsuki needs to face his first day back to school. Or first night back to the dorms, actually. After spending a few extra days in the hospital to recover from the damage his first rut did, and to start growing accustomed with his new body, the doctors decided he should spend a couple of days at the dorms getting used to his classmates before going to class.
They didn’t want to say, but Katsuki could tell how they were anxious about him attacking the extras of 3-A if they came too close. When Kirishima came to see him at the hospital it was touch and go for a moment before Katsuki’s inner alpha recognized the other boy as a beta. Everybody was anxious to see how Katsuki would react to the other students and, worst of all, the other alphas.
The first thing Katsuki realizes when he put foot in the dorm’s common room is how many different smells there are. Bad smells, more precisely. It reeks. Instantly Katsuki’s face twists in disgust. How the hell has he never realized how that room smells like shit? He never thought he’d miss the sterilized scent of the hospital, but he is seriously considering going back there instead of dealing with the putrid scent in the dorms.
Before he can decide what to do about it, Kirishima is already approaching him with way too much energy for Katsuki’s liking.
“Hey bro! Glad to have you back! We were all waiting for you!” he says and, for a second, it looks like he’ll pat Katsuki’s back — a small snarl makes him change his mind.
“Humpf,” Katsuki grunts noncommittally, slowly making way inside the room that’s empty except for Kirishima’s closest friends, Sero and Kaminari.
“We asked everyone to give us some space since we figured you wouldn’t want too many people around when you arrived,” Kirishima says, looking proud of himself.
Hearing that, Katsuki offers a small nod in appreciation. He really didn’t want to meet the whole class at once.
“What’s up, Explodey! New alpha in the zone!” Kaminari celebrates excitedly. Well, at least someone seems to be excited about that. But then again, Kaminari is a beta and, just like Kirishima, will never understand what true nightmare Katsuki just went through.
Sero, however, is an alpha and looks at Katsuki with a bit more sympathy.
“Welcome, dude,” he says, approaching the other three boys.
Katsuki knows Sero isn’t a knotheaded kind of alpha. He’s never engaged in pointless showdowns of territoriality or any shit like that, he’s always courteous to everyone, he never starts pointless fights. And still, the moment the other alpha gets closer, Katsuki’s inner alpha roars.
One thing that Katsuki could never fully grasp before his rut was how the whole ‘inner alpha’ and ‘inner omega’ shit worked. Now he does. It’s like having a wild beast caged inside him. Sometimes the beast is sleeping, sometimes it’s trying to claw its way out; and, as Katsuki learned in that alley, it’s always one wrong move away from taking control.
Something in Katsuki’s scent or posture must have given away how his inner beast wanted to rip Sero to shreds just for daring to come closer. The two beta boys immediately get tense. Sparkles come out of Kaminari’s fingertips and Kirishima’s skin gets a bit harder as both of them get ready to intervene between the two alphas if necessary.
A low growl escapes between Katsuki’s grinding teeth. He hates that he’s doing that but he also doesn’t know how to stop. It takes every ounce of control he has just to keep the beast in check.
Luckily, Sero seems to know what to do. He tilts his head down and to the side, showing Katsuki his neck. And his smell, which was burning in Katsuki’s nostrils, slightly changes, allowing Katsuki to breathe again.
“That’s it. Easy, Baku, I’m not here to challenge you,” Sero says in a calming voice.
Katsuki’s first instinct is to yell at him, saying he doesn’t feel challenged and that this is all fucking bullshit. However, he can’t deny that whatever Sero did, it worked. The beast inside him stopped trying to take control and went back to warily watching everything unfold. So, though Katsuki wanted to say he’s fine and he doesn’t need Sero to submit, he nods again in appreciation of his friend’s actions.
“See? Everything is fine,” Kirishima says as the tension in the room dissipates.
He says it too soon, though.
“Hey, Kiri! Is Explodey here yet? Why haven’t you called me?” Mina’s voice resonates through the room, breaking their very tentative peace.
The moment Mina’s strong, acidic scent hits Katsuki’s nose, he’s already growling.
And this time, unlike Sero, Mina growls back.
It’s all very fast. Mina’s lips curl over her fangs in an instinctive response to being threatened — a response that Katsuki’s inner alpha takes all too personally. As Mina puffs her chest, showing she won’t be bullied around like Sero accepted to be, Katsuki snaps his jaws, ready to take a bite off her.
However, when their bodies move towards one another to fulfill what promised to be a very aggressive fight, the other boys start de-escalating the situation.
“Mina, no!” Kirishima yells, putting himself between the two alphas.
“Chill, Baku,” Sero says, approaching Katsuki with his neck tilted in submission. “She won’t do anything. Relax. You can control it.”
Katsuki turns his face, ready to snap at Sero for whatever reason he manages to vocalize, but Kaminari shows up on his other side to distract him.
“Hey yo, Bakubro! Quite a potent scent you have going on there! Even I can smell you! You’re fated to be a hit with the omegas! You’re gonna have so many falling at your feet that you won’t know what to do with them!”
For everybody’s luck, Sero’s submission and Kaminari’s inane chatter seem to confuse Katsuki’s inner alpha long enough for Kirishima to usher Mina away.
Once Katsuki’s inner alpha calms down, he takes the chance to run up to his room, barely grunting goodbye to his friends. This day was already too much and it has only been less than five minutes. Katsuki hates how he was so close to losing control again over fucking Ashido Mina. It’s so damn stupid! He knows she’s loud and dumb, and that she’s not a threat to him at all — but there he was, a hair away from trying to rip her to shreds until Kaminari mentioned omegas.
It’s embarrassing, but Katsuki could feel the shitty, mindless beast perking up over the promise of having omegas falling for him. Katsuki feels dirty and stupid with how the beast calmed down from just the mention of him taking an omega. He hasn’t thought much about omegas or mates so far. Really, Katsuki hasn’t had the time.
During his rut, he was horny as fuck but it was all muddled with pain, anger, and shame, so it was hard to give any sort of sense to his horniness. And the health workers in the hospital wore all kinds of patches and neutralizers, Katsuki didn’t have the chance of smelling an omega yet.
And from how his inner alpha responded to the idea of it, Katsuki isn’t sure he wants to meet an omega at all. Which will be a problem. Katsuki will be a hero, he can’t avoid every omega in the whole damn society. Actually, forget society — Class 3-A has its fair share of omega students. Round Face, Ponytail, Frog Girl, Frenchie and… Deku.
Shit. Tomorrow will be a shitshow. Katsuki can barely tolerate that bunch on a good day. For fucking sure he won’t be happy with however his inner alpha decides to act around them. There really is no possible good outcome.
Closing his eyes, Katsuki tries to sleep, dreading the day that will come.