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"Bunny, I'm home!" Katsuki announced in his booming alpha voice that made him whine a little inside, toeing his shoes off and dumping his keys in their designated bowl. He knew Izuku was off today and had likely found some sort of project to do.
As the explosive hero trekked into the home, it became apparent that the project was in the bedroom. Frustrated huffs and grunts could be heard, along with a few sniffles.
Katsuki wasted no time, entering the bedroom to see a floppy, messy nest and an absolutely adorably angry Izuku. The blonde sighed, knowing Izuku sucked at making nests and that it was a touchy subject.
"Here, love. Let me help," nimble fingers began weaving the nest in intricate patterns, unbreakable by even the most rigorous of activities. Izuku growled, throwing a pillow against the wall. A pale eyebrow raised in question as he stared at the angry omega, burning wood scent filling the room.
"I'm no good at this omega stuff, Kacchan. You deserve a better omega. Or, I should have been born an alpha or something. I can go to work and protect you all I want, but I can't build a stupid nest," tears spilled over as the omega bore his heart.
These were not new sentiments. Ever since the two presented, they have never matched the norms they were given. Izuku was fierce, protective, territorial, an excellent fighter, and a provider. The way he cared for Katsuki during ruts showed that a good provider he was.
As for Katsuki, that whole feral thing just wasn't for him. He was really good at putting up the front in high school, snarling and growling at anyone who fucked with him. But once he and Izuku mated, it became so much more difficult to hide his desire to build nests and care for their den. Surround himself in softness, burrow into blankets and all that shit.
Don't get them wrong, they both were strong, sturdy, intense heroes. No one ever blinked an eye at them. They were both wildly capable in their own ways, just not the greatest at fitting in to the stupid societal standard they were given.
Large, muscled arms enveloped the slightly shorter greenette, pulling him close to his chest, "You are the best omega. Could you imagine another omega dealing with my nesting shit? Or another alpha having to handle your feral little ass? We got this, Zuku," Katsuki cooed adoringly as he released comforting pheromones, caramel and cinnamon filing the air.
The sniffles slowed as Katsuki could literally feel Izuku thinking, "Kacchan, have you ever wanted to be an omega?"
Katsuki, having worked hard to undo his own emotional constipation, answered quickly and easily, "Fuck yes. All the time, honestly."
"Really?" Shock was seeping off of the single word response.
"Yes, really. I make the best god damn nests, Deku. How could I not consider it?"
"What if we could switch? I could be a big, bad alpha and you could be a...well still big but soft omega?"
Katsuki pulled back to look his omega in the face and found nothing but hesitation and seriousness despite the humorous presentation of the idea.
"What are you talking about? That would be nice but unless you have a magic wand-"
"Have you ever heard of bitching?" Izuku blurt out. At this moment, the alpha realized Deku had been sitting on this conversation.
"I can already tell that you're going to word vomit your research no matter what I say, so go for it," Katsuki led them to their half-completed nest.
"How do you know I've done research? I haven't said anything."
"Those green eyes of yours show all your secrets, De-kuuuu," the taller man booped the other's nose for effect, "Now go on, what do you know about bitching?"
Izuku perked up, thumb and forefinger going straight for his bottom lip, as it always did when he got in the zone like this. It made Katsuki's heart melt.
"Bitching is the process of turning an alpha into an omega, to put it simply, though you probably knew that. A lower gender, a beta or omega, can essentially pump the alpha full of venom and, uhm, mate them. Then, over the next few hours, the change is complete. The former alpha will have a vagina, reproductive system, the, uhm, penis will shrink. So on and so forth." Izuku got progressively redder through his entire explanation.
"Okay, that sounds like some fairytale shit, Freckles."
"I-it's not! Its a valid form of subgender transition. You can do it with hormones and stuff, too. But mated pairs tend to take the traditional bitching route."
Katsuki sat on this for a minute, processing. Izuku must have seen the wheels turning, as he pulled out his phone and pulled up an article from Japan SubGender Science Institute with a full explanation. Crooked hand passed the phone to the alpha, who read with intrigue.
"How long have you been looking into this, Deku?"
The strawberry impersonator seemed hesitant to confess, "Since we presented. I looked it up at the time, since I never really felt like an omega. But when we mated last year, I got pretty serious in my research. It doesn't seem to bother you as much as it bothers me, so I didn't know how to bring this up."
Katsuki looked between the phone and Izuku and huffed an impressed noise as he slouched over, head in his hands, "Zuku, I fucking hate being an alpha. This shit sucks. Ruts fucking hurt, I fucking love building nests, I wanna be the one to carry pups. I just...you know I fuckin suck at expressing shit."
The greenette examined every inch of Katsuki's posture before barreling the pair over in an intense hug, peppering kisses all over the sharp features.
"Oi! What the fuck?!"
"Kacchan, I'm so relieved. Can we do it tonight? Can I bitch you tonight? Want to fuck you with my cock and knot your brand new pussy after I drown you in my venom," Izuku became absolutely unhinged in a matter of seconds. Kisses turned into nibbles and the potent smell of slick flooded the room. Katsuki's dick had literally no choice but to harden up, not that he had any complaints.
"Is it painful?" Katsuki barely sludged his way through his instincts to ask.
"I'll email the agency and ask for 3 days off. If it hurts, we have time to recover. If not, we have time to celebrate."
The grumpy one mulled this over before grunting affirmation at the plan. He had one more question, though.
"Will this turn you into an alpha, too?"
Izuku's head snapped up, eyes blown out and full of other-wordly excitement, "Dumping my venom into you will turn me, I've heard it happens quicker for male omegas since we have a cocklet."
"I would not call the 5 inch rod in your pants a cocklet, Freckles. That's a whole ass dick," Katsuki barked out around a laugh.
"Good, it'll make it easier to knot you then," Izuku made no hesitation to bite down hard on Katsuki's mating gland, the gentle sting of venom warming the alpha's neck as more and more was pushed into the wound.
Katsuki released a shout of pleasure, his dick spurting pre into his boxers. Frantic hands made quick work to shed all of their clothing, even going to far as to tear pieces straight off the muscular bodies.
Izuku's actions were feral and hungry. Once he was content with the amount of venom pumped into the mating gland, he moved to the other side, the sting traveling with his fangs. Katsuki was starting to feel loopy, the intensity of the ecstatically aroused omega scent and venom pouring into his veins making his head float.
His dick ached from lack of touch and all of the things going on around them. Almost as if he knew, which somehow he always did, Izuku trailed his hand down until his fingers wrapped around the neglected length. A gasp left the omega's mouth.
"Kacchan, look! Your dick is smaller already!" The greenette announced as he unattached himself from the other's neck and moved for his left wrist. Crimson eyes opened, not sure when they shut, and peered down to his cock.
Holy fuck. It was smaller. And no knot in sight despite Katsuki feeling like he was already teetering on the edge.
Fangs pierced the scent gland on his wrist and the former alpha arched his back off of the bed, pleasure coursing through him in waves. Sure, it stung like hell, but in the best ways possible. A rumbly purr emerged from his chest. He could purr before, but this was different. Easier and more fulfilling.
After another few moments, Izuku popped off the gland once more, licking the wound before moving to the other wrist, "good omega, doing so good for me baby. I can see you opening up for me, so pretty Kacchan."
To ensure his statement was made clear, a crooked finger sunk down to trace a new, wet opening formed under Katsuki's shrinking cock. When had his balls disappeared?!
That thought was very fleeting due to Izuku's fangs biting into the next scent gland. Katsuki felt an intensely euphoric wave begin at his toes and travel up his body, useless cum shooting from his cocklet and slick filling the room. It smelled like caramel apples. He absently noticed his voice had a smooth, melodic sound to it as he roared through his orgasm.
Purrs continued once he was done riding his high. Katsuki became aware of Izuku murmuring to him, "Almost done, my beautiful omega. You are doing so good for me, love. Your alpha is going to take such good care of you."
Katsuki felt his useless dick begin to harden once more as the greenette trailed kisses all over his body, grounding him and giving him a moment to rest. He clumsily lifted his head, "Are you changing?"
Viridian eyes met his own, shining with confidence, before he stood up for a brief moment.
Holy fuck that was never going to fit.
What was an impressive 5 inch omega cocklet was now at least a few more inches and girthy. The makings of a knot at the base made Katsuki's head swirl even more than it was already. He allowed his head to fall onto the nest with a sinful groan.
Izuku chuckled, probably well aware of the other's thoughts in this moment, "You've got this, baby. You're being made specifically for me and my cock."
Katsuki whined, a little overwhelmed and overstimulated in all of the most incredible ways.
"Ready for the last two, baby?" Izuku said as he got on his knees between smooth, milky thighs.
The blonde could only nod and squeak out a confirming grunt. Soft kisses and nibbles trailed from his knee all the way to his thigh, teasing the scent gland with little kitten licks. He squirmed under the action, Izuku's teasing so desired but so torturous.
Fangs once again found home in Katsuki's body. He jerked and wailed pornographically at the intrusion, warm venom going straight to his...pussy? That had to be what that was. Katsuki's own hand traveled down to investigate his changing body.
Immediately, he found he was slicking up an absurd amount for what was essentially a new omega. His lips were puffy and sensitive, a hole being carved out of muscle within him. It was so bizarre, but even more bizarre that none of this was as painful as it seemed it should be.
A scarred hand gently formed over his own, moving his fingers as if to demonstrate how to pleasure himself. The assisted action brought Katsuki to the brink once more, which the fucking green-haired asshole must have sensed because he pulled away.
A desperate whine escaped the omega.
"Don't worry, I got you," Izuku cooed in a much deeper, rumbly voice. His hand once more found Katsuki's folds and explored without the omega in the way. The practiced motions driving Katsuki insane. It was just enough to keep him on edge without allowing him to find release.
Crooked fingers curled inside, finding all of the new and sensitive spots that Katsuki was looking forward to mapping out. For now, all he could do was moan and writhe underneath the skilled hands of his alpha.
"Look at you, opening up for your alpha. I wasn't sure if you could take my cock today, but now I have no doubt I can knot you," Izuku spoke with such reverie that Katsuki felt his entire torso and head flush at the praise.
"One more, you're going to cum on my fingers when I bite down, okay omega?" the sentence wasn't a traditional command, but delicately laced with one. Submission and affection pooled in Katsuki's gut.
"Yes, alpha! Please!"
"As you wish," crooked fingers sped up their motions as kisses lead to a vicious bite. Katsuki almost flew out of their nest with the speed his back arched, vision whited out as orgasm over took him. This was so much different than knotting. His entire body rippled with pleasure.
The venom felt more potent on this final bite, burning with the intensity of the omega's own explosion quirk. The pain could only register as pleasure as the omega rode out the final waves.
"Good omega, you're doing so well. Such a submissive princess for me. But we aren't done yet," the deep, commanding voice rumbled once more. Steady hands flipped Katsuki and maneuvered him into a traditional presenting position.
"Izuku, knot me, please! Please, need your knot!!!" Katsuki cried as his whole body heat up.
"Ohhh, Kacchan, did I put my pretty little omega into his first heat? Poor baby, let your alpha make it better," Izuku preened with a hint of smugness woven into his words.
"Alpha, alpha please, need you," the omega continued to whine.
A firm, round, warm object pressed against the new hole. Katsuki figured it had to be Izuku's cock and anxiety began to bubble.
Of course, the fucking nerd knew. He began to rub Katsuki's lower back slow and comforting, "You've got this, Dynamight."
The alpha had always known exactly how to encourage the blonde, even if it was fucking cringey. He took a deep breath and pushed back on the intrusion, a slick pop followed the delicious pressure brought by Izuku's tip entering the virgin hole.
Air was punched out of the omega. He wasn't sure what to expect but damn.
"Doing okay, baby?"
"Yeah yeah, keep going!" Katsuki whined impatiently, letting Izuku know he was still coherent.
A lighthearted chuckle was heard from behind, "Okay, Kacchan. I'll go slow."
And slow did he go. Painfully slow. Katsuki purred and whined, practically begging for the alpha to go faster. But at the same time, the omega basked in the stretch. The delicious way Izuku's new, stupid huge horse cock carved it's own space into Katsuki's new body.
It felt so right. Like this is how it was always supposed to be.
He was lost in the sensations and barely registered when Izuku's hips smacked against his presented ass, fully sheathed in the new pussy. The jiggle of his own cheeks was a surprise Katsuki hadn't thought of. Did his ass get bigger?
"Ohhhh Kacchan. I don't know if I can do this. I...I don't want to lose control and hurt you," Izuku panted, clearly wrestling with his own instincts and needs.
The omega pondered that for a moment. Could he be hurt? He hadn't felt any discomfort since the venom receded. He was never one to take the soft way of life.
He wiggled his ass, pushing back on the cock invading him, "You saying I can't handle you?! Hah?"
Firm, big hands stilled the motion, "Katsuki. I am barely holding back."
"Then don't. Give me your all, alpha."
You could almost hear something snap. Izuku set a relentless pace, the squelching slap noises reverberating across the bedroom. Their joint groans creating a lewd symphony that Katsuki lost himself in.
Izuku shifted, angle changing just enough to slam Katsuki's g spot with fervor. Wails and shouts left the omega, completely oversensitive and trying to adjust to the new sensations.
One of the alpha's fingers found it's way to the omega's pathetic cocklet and began rubbing it fiercely.
"You're going to cum on my knot, omega," Izuku commanded, causing Katsuki to take notice of the knot bumping against his entrance, trying to make room for itself.
The omega obediently spread his legs further to give the knot space to enter. Izuku gasped at the sudden change, knot locking in place. Katsuki came with a scream, walls pulsing and milking the knot until Izuku fell over the edge as well, hot spend flooding the newly developed womb.
It felt like ages before the alpha's cock ceased it's barrage. Like the good alpha he was, Izuku gently picked up Katsuki with inhuman ease and settled them in the center of the nest, tied together with the life-affirming knot.
"That was...oh my god," Katsuki rasped out around ferocious purrs.
A chuckle, "I should have brought up bitching years ago."
"Yeah, stupid nerd holding out on me," A weak smack was given to the alpha's arm. "Hey, did you grow? You feel...bigger."
"Yeah, I think so. I noticed when I was, uhm, fucking you, that I could basically eclipse your body."
Katsuki purred louder until he ceased, "wait, did I shrink?!"
Izuku roared with laughter, "No, I don't think so. Your hips and butt grew though, and maybe your tits too," he informed the other excitedly.
"Good," Katsuki keened as he let sleep take him.
They'd need their rest for their first heat and rut with their newfound, fulfilling roles.