Chapter Text
"Aren't you usually in the gym by five?"
"Go fuck yourself," Katsuki answered as he grabbed the can from the bottom of vending machine, popping the tab and taking a drink. Denki shook his head.
"Seriously man, you never miss morning training! And since when do you drink coffee?" Denki scolded, swiping a card across the machine's reader and punching in a order code. Katsuki squinted at the combination, his brain slowly coming back online with the caffeine.
"Since whenever the fuck I feel like it. Since when do you drink green tea?"
"Oh, this?" Denki rubbed the back of his neck sheepishly as the machine whirred, the can falling to the bottom with a hollow thunk. "I don't," he admitted, taking the can. "This is for Izuku. He mentioned liking this brand last week, so I figured I'd grab him one, y'know?"
"He's been obsessed with those since he found them," Katsuki said, thinking of how often he'd seen the same brand in Izuku's dorm room over the past few weeks. The thought of Izuku made him rub at his tired eyes in frustration; though it wasn't Izuku's fault, he was the reason Katsuki had skipped training and partaken in a vice like coffee this morning. For the past few days, Katuski had been sleeping poorly; strange dreams kept him restless during the night and waking still tired. Strange dreams of Izuku. Of his laugh, his eyes, his hands...his mouth...
Katsuki shook his head to clear it, heading towards the classroom. He didn't know why he'd suddenly started having dreams about making out (or more) with his best-friend-turned-bullying-victim-turned-rival-turned-best-friend-again-somehow, but what he did know was it had to stop. The fact the he'd been able to get close to Izuku again despite what a prejudiced shithead he'd been for almost ten years - that Izuku had the grace to forgive him and the kindness to be his friend again - was already a small miracle in and of itself. Katsuki didn't need to muddy the waters by making things weird between them. Especially considering...
No, Katsuki scolded himself, drinking the last of his coffee in the hope that the taste would distract him from his thoughts of Izuku (it didn't). No way, he wasn't going down this rabbit hole of thoughts again; maybe if he hadn't been thinking about weird things like this in the first place, he wouldn't be having weird dreams at all. He just needed to focus on something other than Izuku today.
This plan was quickly derailed the moment Katsuki and Denki walked through the door. Like always, Izuku was at the desk behind Katsuki's, and like always, Izuku was the first thing Katsuki's eyes found in the room. Shoto was sitting next to Izuku's desk, which wasn't unusual; the two of them were close friends, too, after all. He'd even pushed his desk closer to Izuku's across the aisles of desks, comparing their notes against each other.
Katsuki knew jealousy wasn't a good look on him, and tried not to let it show, but he still felt it. Logically, he knew it was good Izuku made friends easily at UA; he'd never had many (any) friends before, which was entirely Katsuki's fault for ostracizing him after he'd been diagnosed quirkless. Izuku was happy, well rounded, and had a lot of support now that he had a robust social net. Katsuki knew that, but it was still hard to shake a feeling of possessiveness; the feeling of wanting Izuku all to himself.
Once upon a time, he'd had that. When the two of them were little, playing heros-and-robbers and sharing crayons and squabbling over who's quirk would be better, Katsuki had been Izuku's best and only friend. He'd been a big enough idiot to throw it all away to look cool in front of people who didn't even matter, and had lost Izuku as a friend entirely for almost a decade. He was grateful as fuck to have gotten than back at all, and even if he and Izuku had stayed best friends from the time they were in diapers until this moment, Izuku would still need other friends. It didn't make sense for Katsuki to have him all to himself, of course; but he still felt jealous. It was just something he'd need to grow out of, but he could admit it was...a work in progress. He'd always been weirdly possessive of Izuku, actually; even when he'd bullied him in middle school. Even when they were just kids. Even before-
Katsuki's thoughts were interrupted by Izuku's laughter, grinning at something Shoto had said. Though he turned his attention back to his notebook after a moment, Shoto's attention stayed on Izuku; quite intensely, actually. Eijiro, who had also just gotten to class, ambled over without even taking his backpack off, leaning over Izuku's desk and pointing out something in his notes, getting him a dirty look from Shoto in the process. Which was...weird. It wasn't unusual for Alphas their age to butt heads sometimes, especially around Omegas like Izuku, but Shoto and Eijiro were friends. They didn't fight over Omegas the way two teens who weren't close might.
Something wasn't right. When Denki went over as well, pushing Eijiro out of the way a little to set the can of green tea on Izuku's desk, that was enough for Katsuki.
"Hey blockheads," Katsuki said with a scowl, coming closer, "what the fuck is your damage? Why are you acting like a pack of-" he cut off as he came closer to Izuku's desk, taking a breath in. Then a deeper one.
He dropped the empty can of coffee with a hollow clatter onto the floor of the classroom, crossing the rest of the distance to Izuku's desk in three long strides, pushing Shoto's desk out of the way with one hand and grabbing Izuku's wrist with the other. He pulled Izuku out of his seat and towards the door.
"Katsuki, what-" Izuku began, clearly startled, but he was cut off by one of the boys hovering over his desk growling. Katuski spun around, pushing Izuku behind him and snarling back, teeth bared; he could feel that his fangs had extended, too. He didn't know which of them had growled, but all of them drew back a bit at that, a little bit of the fogginess clearing from their expressions.
If he'd been a little more present of mind, Katsuki would have been embarrassed about baring his fangs at his friends; in front of the whole class, no less. As it was, though, he was only thinking about one thing; the boy he was currently dragging out of the classroom and down the hall.
"Katsuki!" Izuku protested, not pulling back against Katsuki's grip and hurrying to keep pace with him, but perplexed nonetheless. "What are you doing? Where are we going?"
"Recovery Girl's office," Katsuki grunted, trying (and failing) not to breath in deeply. Not that it would help much. He was already hard. Thank god these pants didn't show it easily.
"What? Why?" Izuku questioned. "I'm not sick!"
"No, idiot," Katsuki ground out, glancing back at Izuku. His eyes were puzzled, his face flushed, and his scent was so potent it was making Katsuki's head swim.
"You're going into heat."
---
"But I take suppressants!"
"Long term suppressant use can reduce the medicine's effectiveness," Recovery Girl replied dryly, looking through Izuku's chart, "though there are supposed to be scheduled breaks to prevent such problems." She glanced up at Izuku, eyebrow raised. "When was the last time you had a heat cycle?"
"I..." Izuku fidgeted, and Recovery Girl sighed.
"Medicine isn't something to play around with, Midoriya-san. You're going to put your health at serious risk if you keep doing things like take your suppressants even though you have a break scheduled."
"Are you an idiot?" Katsuki hissed, punching Izuku on the arm carefully; he hadn't put his hands on Izuku with the intent to hurt him in a long, long time now, and never would again. Recovery Girl still gave him a dirty look.
"Midoriya-san, are you sure you don't want to speak privately?"
"Positive," Izuku said without hesitation. Then, more timidly, "I didn't mean to cause an issue with the medication, I just didn't want to miss class, and scheduling around breaks is tricky..."
"The other Omegas in our class schedule them just fine," Katsuki scolded.
"To be entirely fair," Recovery Girl said, flipping through Izuku's chart with raised brows, "the other Omegas don't have the same circumstances as Midoriya." She looked up at Izuku. "When did you form a partial bond?"
"Erm...when I was four," Izuku said, rubbing at the back of his neck sheepishly. Recovery Girl's eyebrows somehow climbed higher.
"With who?"
Izuku, the master of subtly, openly glanced at Katsuki, then flushed and looked away. Recovery Girl looked confused for just a moment, then understanding fell across her features.
"I see," she said in measured tones. Katsuki could tell she was surprised; most people were, when they found out. Bonds between teenagers were unusual these days, after all, and their situation was even more unusual than that. "No wonder you wanted Bakugo-san present, with a partial bond between the two of you."
"What does that have to do with the bond?" Katsuki asked, puzzled. He'd assumed Izuku wanted him in the room as a "patient advocate", as Izuku had phrased it, because of nerves. He'd been skittish about doctor's offices for as long as Katsuki could remember; Izuku had let it slip once when they were going over notes together that he'd developed a fear of going to the doctor ever since the appointment where he was diagnosed quirkless as a child (which made Katsuki feel like total shit; being quirkless was hard enough on Izuku without Katsuki having piled all of his bullshit on top of it, too).
"Soul bonds, even partial ones, change the dynamics of heat and rut," Recovery Girl said, her tone clinical and matter-of-fact. "For both parties, being apart during the most fertile period of their hormonal cycles can cause distress and discomfort at heightened levels as opposed to unbonded individuals. Bonded individuals also shift their scent so that their bonded partner can smell them more intensely than other Alphas or Omegas."
That actually kind of made sense, Katsuki thought. He'd only gone through a few ruts, but he'd noticed he was really pissed off during them, more so than other Alphas seemed to be during their ruts, from what he'd gathered from discussions with his peers. He'd always chalked it up to his particularly volatile temperament, but the bond being the reason made more sense; especially considering that the only thing that soothed his temper during ruts was texting or calling Izuku. His other friends and him still kept in touch, too, and though talking with Eijiro or Denki also provided a welcome distraction from the boredom of being locked away like a princess in a tower and the frustration of constant arousal, Izuku was the only one who's voice soothed Katsuki's rage like a balm on a burn. Not only that, but Katsuki was the only one who'd been able to tell Izuku was going into heat; his scent was more pronounced to the other Alphas on the cusp of heat, of course, which was why all his Alpha classmates had been hovering over his desk that morning like a bunch of knotheads, but they acted as if they were drawn to him subconsciously. Though the three of them were Alphas, and Izuku an Omega, they were friends first and foremost. If any of them had been able to tell Izuku was verging on heat, they would have taken him to the infirmary, too; it had happened before with other Omegas in the class.
"Regardless, you'll need to go through a heat now that one has started," Recovery Girl said, "and you have to stop skipping your heats if you want your suppressants to remain effective for you."
"But my heats are so long, and midterms are coming up!" Izuku protested. "Can't we use an emergency inhibitor?"
"Boy, I knew you were self-destructive ever since you were breaking your bones using your quirk, but that's the most foolish thing I've heard in a while," Recovery Girl snapped. This was beyond her typical scolding; her expression was severe, and her voice even more so. "I wasn't kidding when I said that medicine isn't something you play around with. Estrous cycles are a deeply rooted survival behavior, evolved to ensure the propagation of our species. It's hardwired into us, and it's certainly not optional. As an Omega, I've been through my fair share of heats, and I can't say I enjoy the discomfort more than any other Omega does. But as a medical professional, I've also seen what happens to Omegas who abuse suppressants. Make no mistake when I tell you you're quite literally putting your life at risk with the paths you're taking."
Izuku ducked his head in shame, and though Katsuki felt bad for him, he also knew Recovery Girl was right. More than once, he'd seen a news story about an Omega overdosing on suppressants; usually a high-level executive, someone whose job didn't allow for a lot of time off. Heat and rut leaves were mandated by law, but a lot of corporations quietly discouraged employees from using their leave time due to lost productivity. Attitudes were changing a little in the modern day now that the damage that abusing suppressants could do to people was being brought more to light by science; though it was slow, it was still progress.
"How long are your heats typically?" Izuku was quiet for a long moment, and Recovery Girl's expression shifted from stern to horrified. "God in heaven, don't tell me this is your first?!"
"No!" Izuku exclaimed. "I've had a...few before, in first and second year of high school. I've just been skipping this year to try to keep my grades up. They're usually two weeks, which is longer than I wanted to be out of class."
Recovery Girl looked contemplative at that. "Two weeks is certainly on the longer side of the scale," Recovery Girl hummed, "though it's not unheard of, it's certainly outside the average." She eyed Izuku, then Katsuki. "The bond likely is what's causing the extension."
Izuku reddened, but Katsuki was just confused. "What does that have to do with the bond?"
"For someone unmated, a heat or rut usually lasts about a week," Recovery Girl explained, "but for a person already bonded, particularly Omegas, the fertile period can be extended if their partner isn't present. The purpose of heats is, after all, to further the species." Despite the clinical manner of her speech, Izuku's face reddened a deeper shade at that, enough that his freckles were hidden like stars during the day. "So, if that goal isn't fulfilled in the typical period, the body may release hormonal signals to extend it." She glanced at Izuku, seeming unperturbed by his cherry-red face. "However, the bond could also work in your favor. Just as it's possible to extend heats to up to two weeks in the absence of your bondmate, you can also shorten them to just a few days if your bondmate is with you."
"So if I and Izuku hang out together during his heat, it could be over in a weekend?" Katsuki asked.
"Is that what the kids are calling it these days?" Recovery Girl arched a brow. Now it was Katsuki's turn to redden. "But yes. Due to the partial bond, if the two of you engage in intercourse during his estrous cycle, it will shorten the heat. Being in close proximity to each other will also significantly reduce discomfort on Midoriya's part." She looked at Izuku. "Is that something you want to pursue?"
"No way," Izuku said hurriedly, waving his hands in front of him in refusal, and Katsuki fought to keep his face neutral, keep the hurt off of his face. Izuku was his own person and he could spend his heat however he damn well wanted; but Katsuki couldn't deny that it still stung that despite the practical benefits it would offer, Izuku still rejected it without a second thought. "I couldn't inconvenience Katsuki like that. It isn't fair to make him fall behind in his studies for my sake."
"You think I'm some fucking extra?" Katsuki said lightly, bumping his shoulder against Izuku's. "I could be out of school for a month and still place top three in midterms." He'd just meant to lighten the mood, to distract from the fact that the school nurse had basically just suggested that Izuku and Katsuki fuck each other, but the tension only increased. Izuku's eyes widened, and Katsuki realized that instead of making Recovery Girl's plan sound crazy, he'd accidentally just lent it validity by saying it wouldn't make him fall behind.
"...But that would be crazy, right?" Katsuki hurried to add, giving Izuku a strained smile as he shook his head, turning back to Recovery Girl. "What, would UA lock us up in an empty classroom with a mattress and a bunch of condoms?"
Izuku giggled at that, and Katsuki felt a flash of satisfaction at having broken the tension and made Izuku laugh. However, Recovery Girl answered his sarcastic question as if it had been serious.
"No, there are hotels that bonded pairs use," she replied, "and while it's unusual, especially these days, you two aren't the first bonded pair we've ever had at UA, so we have experience with this kind of thing. Besides that, as the primary biological function of heat is to result in pregnancy, use of contraceptives like condoms wouldn't achieve the goal of reducing the length of the heat."
"So I actually would have to get pregnant?" Izuku exclaimed. His face wasn't flushed anymore; he'd gone somewhat pale, in fact.
"That would be ill-advised, as you're still a student," Recovery Girl responded calmly, "and also extremely unlikely, considering you and all Omegas enrolled in UA receive an annual contraceptive injection as part of the vaccination schedule. The shot remains effective for a year, and while we usually advise two forms of birth control, such as condoms, the fact that you're trying to shorten a heat means you need to have intercourse to completion, so just one will have to suffice."
"Is the shot 100% effective?" Katsuki asked.
"Considering Izuku doesn't have any conditions that would reduce the effectiveness, and that the shot was administered recently, I would say there's an incredibly low risk of a pregnancy resulting from unprotected sex at this time," Recovery Girl answered.
"Katsuki, are you seriously considering this?" Izuku exclaimed, his face back to red with embarrassment. Katsuki shrugged, trying to appear nonchalant even while his heart raced in his chest.
"In the end, it's up to you, since it's your heat. But if it would help you, I don't see why not."
"Your parents would never let you take time off from school for something like...like that, would they?"
"Seeing as both of you are eighteen now, parental consent isn't necessary," Recovery Girl cut in. "The only people who would need to consent are you two." She checked her pager, even though Katsuki hadn't heard it go off once since he'd dragged Izuku into her exam room. "Now, if you two will excuse me, I have other things I need to attend to. Let me know when you decide." With that, she hobbled out of the room, closing the door behind her.
Other things my ass, Katsuki thought with amusement. She just wanted to give the two of them privacy, which he was grateful for; talking with his elderly school nurse about having sex with his childhood best friend was awkward as hell. To be fair, though, the two of them all alone together after she'd just finished telling them what a great idea it would be for them to have sex with each other was also awkward as hell, too.
Izuku was the one who broke the silence. "Well, I..." Izuku chewed on his lip, seemingly thinking things over, and Katsuki felt his heart skip a beat. "I...can't ask that of you, Katsuki," he finally said, and Katsuki fought to keep the disappointment off his face; this was Izuku's choice, and if he said no, that was that. "I don't want to be a burden, not when you and everyone else already do so much to help me."
The use of burden made Katsuki frown. Izuku had always been selfless, but since he'd gotten his quirk, he'd gone beyond just selfless to self-sacrificing. He wouldn't hesitate to put himself through hell if he thought it would help someone else, even the slightest bit. Katsuki couldn't tell if this was Izuku trying to politely reject him, or if he was just trying to refuse help because he thought it would be inconvenient for Katsuki.
"It's fine if you wanna be alone during your heat," Katsuki started cautiously, picking his words carefully like he always did when Izuku was being stupidly self-sacrificing, "but you wouldn't be putting me out to help you."
"You don't have to feel obligated to help me, Katsuki."
"It's not out of any sense of obligation," Katsuki clarified, "it's out of a sense of wanting to help my friend. You aren't a burden, Izuku," Katsuki said firmly, turning to face Izuku fully, holding his gaze. "Not to me, and not to any of your other classmates. We study together, we train together. We help each other. It's not a chore, it's part of friendship."
"But..." Izuku floundered, "It - sex - is a big deal, right? I haven't before, and..."
"I haven't either," Katsuki confessed, "but the really important thing is that you like and trust the other person, right? You're my best friend, Izuku, and you're my teammate. I like spending time with you, and I trust you with my life on the battlefield. Is this really that different?"
"I'm thinking there would be less fighting villains. Or hoping so, at least."
Katsuki laughed with delight, grinning at Izuku's wit and wrapped up in his smell and so in love it hurt. Izuku grinned, pleased that Katsuki laughed at his joke, but sobered quickly.
"But..." Izuku wavered, and Katsuki's heart beat a rapid maybemaybemaybe as Izuku fidgeted. "...Do you want to?" Izuku asked after a long moment; almost shy. It was so cute Katsuki could have kissed him.
But he didn't. Izuku didn't like him like that, after all. The fact that they were even friends after all the hell Katsuki had put him through in their younger years was a miracle; the fact that Izuku considered Katsuki a good enough friend to trust him with something like this was even more so.
Instead, Katsuki just gave a simple nod and a smile. "Yes," he said, wishing he could say I love you instead. "I do. Do you?"
"I...I do, actually," Izuku said, voice shy but sure, and Katsuki fought not to break out in a dopey grin, feeling his heart beat double-time. "Let's go get Recovery Girl."
---
"I wanna play the Blue Ranger this time, Kacchan!"
"The Blue Ranger?" Katsuki asked, picking up a red mask with a children show's character's design on it. The early afternoon sunlight glinted off the hard plastic, and he squinted, rubbing the sting out of his eyes. "The Blue Ranger is an Alpha, they say so in the show."
"That's okay," Izuku replied, picking the mask up from the grass, an array of Katsuki's toys strewn across the yard, as was common when Izuku came over for playdates. "When I grow up, I'll be an Alpha, too!"
Katsuki shook his head as Izuku pulled the blue mask on. "Nuh-uh. When you grow up, you're gonna be an Omega. Like the Green and Purple Rangers are."
"How do you know?" Izuku asked, voice muffled by the mask but his tone curious, tilting his head to the side.
"I can smell it," Katsuki replied simply.
"You can?" Izuku brought the collar of his shirt to his nose, removing the mask so he could sniff the fabric. He looked at Katsuki accusingly. "I don't smell anything, Kacchan! My mommy is an Omega, and so is Mrs. Nakayama at school, and I don't smell how they do."
"That's cause it's not on your shirt," Katsuki answered, rolling his eyes as he walked over. "It's on your neck. Right here," he punctuated his sentence by brushing his fingers over Izuku's nape.
"On my neck?" Izuku reached up, touching the back of his neck exploratorily. "Where a bite would go?"
"Yeah," Katsuki answered, leaning in and smelling Izuku again. "You smell good. Sweet. Kinda like strawberry ice cream."
Izuku brought his fingers that had been mapping the back of his neck to his face, smelling them. A disappointed frown turned down the corners of his mouth. "I still don't smell anything," he complained. "How come you can smell it and I can't?"
"You're probably used to it," Katsuki shrugged.
"My mommy says I don't have a scent yet. How come no one else can smell it?"
"I can smell it more since we're gonna be mates when we grow up."
"We are?" Izuku said, curiously, and Katsuki nodded. "I like that idea!" Izuku said with a grin, "cause then me and Kacchan get to play together every day!" He twirled in delight, then stopped abruptly, looking at Katsuki. "Does that mean you're gonna bite me?"
"Yeah," Katsuki said, reaching out and brushing Izuku's nape again, where he'd seen the scars of his own parent's mating bites, where Izuku's scent was strongest, "right here."
"When?"
"...I don't know, actually," Katsuki admitted. "Should I bite you right now?"
"Does that mean we'll be mates and can play together every day?" At Katsuki's nod, Izuku mirrored the gesture enthusiastically. "Okay!"
Izuku tilted his head forward, the way people did in movies sometimes, and Katsuki leaned in, settling his teeth against Izuku's neck and biting down, like the most natural thing in the world.
A few moments later, he pulled back, wiping his mouth off with his shirt sleeve and, after seeing the pinpricks of blood welling up around his teeth indentations in Izuku's skin, dabbed at the blood there too, dotting his shirt with red. "Sorry," he said; despite the bite being intentional, he knew he was supposed to say sorry if he made someone hurt. "I made it bleed a little."
"It's bleeding?" Izuku said, reaching back and prodding at the back of his neck, fingertips coming away stained red. Instead of looking frightened or crying, like he usually did when he scraped his knee or when he'd gotten a paper cut at school, he simply looked puzzled. "But it didn't hurt!"
"Well, then it's probably okay then," Katsuki decided, peering at Izuku's neck again, the flow of blood already starting to dry up. "Plus, the bleeding almost stopped already." He wiped the rest of the blood up with his sleeve, leaving only a few red smears on Izuku's skin. He picked up the red mask from where he'd dropped it on the grass. "Wanna play more Hero Rangers?"
Izuku wiped his hand on his pant leg, slightly darkening the denim, before picking the blue mask back up from where he'd dropped it on the ground. "Only if I can be the Blue Ranger!"
"You can be any color Ranger," Katsuki said. "Let's go get the bad guys!"
---
"What's on your sleeve?"
"Blood," Katsuki replied with his typical straightforwardness. Mitsuki gave him a disapproving look.
"Were you fighting again?" she asked, crossing her arms. "I tell you all the time not to fight with Izuku."
"We weren't fighting," Katsuki said, Izuku sitting on the couch as his mom, Inko, helped him put his shoes on, the two of them preparing to leave. "I bit him."
"Katsuki!" Mitsuki shouted as Inko turned towards them, startled by Katsuki's confession.
"What?" Inko exclaimed. "Izuku, did Katsuki bite you?" At Izuku's nod, she demanded, "where?"
"On my neck," Izuku replied, pointing to his nape. Inko froze, then pulled Izuku's jacket down to reveal the back of his neck; a few streaks of red still smudged across freckled skin, next to an already-scabbing bite mark.
"Katsuki!" Mitsuki shouted the moment she caught sight of the bite. "You don't bite your friends! Why would you do that!?"
"I bit him so we can be mates!" Katsuki answered, like the answer was obvious. Mitsuki groaned in exasperation.
"That doesn't work when you're kids! You have to wait until you're grown up to form a bond! Biting when you're a kid only hurts!"
"It didn't hurt," Izuku spoke up from the couch, where he'd been watching the drama unfold with no small amount of confusion. "Not even a little, like a poke from a shot at the doctor's."
Total silence. Inko, Mitsuki and Masaru exchanged uneasy looks over the children's heads.
"There's no way," Masaru said after a long moment. "They're only four, after all."
"The bite is dead-center on his nape, though," Inko said anxiously, "and there have been cases of children - not as young as four, but still young..." she trailed off.
"...At any rate, we should probably go to the clinic, just to be sure," Mitsuki said after a moment. "If nothing else, they'll be able to clean up Izuku's neck. Figure out why it didn't hurt. Maybe Katsuki hit one of Izuku's nerves, or something."
"It didn't hurt cause we're mates," Katsuki said, rolling his eyes. He didn't understand why they had to go all the way to the doctor just to hear the exact same thing, but he didn't fuss when his mom made him put his jacket on and drive with Auntie Inko and Izuku to the doctor's office.
He got to sit next to Izuku in the backseat, after all.