Chapter Text
Katsuki entered his room gruffly, nearly slamming the door as he shut it. He immediately flopped down on his bed, feeling entirely exhausted. Did Deku get injured before they switched bodies? His body hurt like hell. He felt the burning the strongest in both his arms, it was almost unbearable.
Sitting on his bed, he looked down at Izuku's scarred arms. Some were just little white lines, others were big white gashes against the boys' tan skin. Izuku really put his all into training his quirk, looking down at Izukus's body he took note of Izuku's biceps, his forearms, and his shoulders. He carved out his top half pretty well with all his training but the real kicker, everybody knew, was his legs.
To be honest, Izuku was pretty built. He would've been a fool not to see the growth of his childhood friend, in fact, he was a little too aware of it. He watched Izuku hone his body along with his quirk, watched the boy's jaw get sharper, and watched him grow inches. But obviously, that nerd could never beat his actual body. Katsuki relished in the fact that he was still towering over the other boy, not that Deku was short by any means. Deku was pretty tall but that just made being taller feel even better.
The first time he noticed the change in Deku they had been sparring, and Izuku had managed to wrap his legs around Katsukis torso. Then he squeezed. Oh my fuck, Katsuki almost passed away.
Ever since that day, he paid attention to the nerd's growth, watched his quads grow, and even his calves were sculpted perfectly. Though Katsuki tried not to let himself in that area, he knew everyone did. Izukus glutes were just too perfect not to look, he even heard Denki thirsting over them with Kirishima once. His whole body looked as though he was sculpted by god himself, every scar, every curve, every bulge.
Never could Katsuki look as close as he was now. He stood and walked over to his full-body mirror, shocked at his reflection. He knew he was going to be greeted by Izuku staring back at him, but never had he thought he would see such an upset look on his face. Obviously, he knew it was him making that expression but it was just something he wasnt used to seeing on Izukus face. Immediately, he forced his face to relax, happy to see Izukus resting face.
He lifted his shirt looking down, tan abs, and a strong v-line stared back up at him. He tentatively brought a hand over to touch his stomach. Sure, he's seen Izuku shirtless countless times but he's never been able to actually touch them. He watched as a scarred hand traced his abs, the v-line. He let out a small gasp, reveling in the sight of Izukus's perfect body. Was it natural for someone to be so perfect?
He looked back up at the boy's perfect face in the mirror, green hair disheveled like usual, and a blush dusted his cheeks. He loved how easily Izukus face flushed, but his face flushing because he looked down at his own abs is laughable. And honestly embarrassing. Izuku would never know though.
Damn. Izukus arms hurt really bad. Was his body always this painful or is something wrong? Katsuki contemplated texting the other boy, he would probably know the answer. On the other hand, he couldn't bring himself to talk to the boy after thirsting at his body in the mirror, so he settled on getting ready for bed.
He grabbed pajamas and headed for his bathroom, turning the shower on. He didn't care whose body he was in, they would not be getting under the covers of his bed dirty. He did feel a little embarrassed about being naked in Izuku's body, the fact that he had to clean it himself. At the same time, he was also a little excited to see how much Izuku was packing, and a little nervous. What if it was bigger than his? If Izukus junk was bigger than his he was 100% going to off himself in Izukus body, hoping it would take out the both of them.
He stripped the other boys clothes off, not looking down. Oh my gosh, he was so fucking embarrassing. He needed to realize that he wasn't taking the clothes off of Izuku like it was actually him, he's taking the clothes off of himself for fucks sake. So why the fuck did he feel so jittery.
He got in the shower and let the steam envelope him, hot water running over his aching arms. The heat of the water soothed the pain almost instantly, it was still definitely there but now it was a background noise. He hummed to himself as he grabbed for the shampoo, pouring a good amount into his hand before putting it into his hair. Izukus hair felt soft between his fingers as he rubbed the shampoo onto his scalp, he would've thought the nerds hair would've been a knotted mess but there was no knot in sight. So Izuku wasn't lying when he said he did brush his hair and that it just looked like the crazy mess it was on its own, he thought to himself. He moved on to washing his face. He knew he was avoiding washing the boys body, Katsuki still hadn't looked down.
Now done with every other task, he had to grab the body wash. He lathered up a wash cloth with his soap and started at the boys arms. He cleaned every inch of both arms, still admiring their definition, before he moved on to Izukus chest. He hadn't really noticed before but Izuku had pretty big pecs and cute little nipples. He stared at them for a second, wanting desperately to touch them but he restrained himself, focusing on washing the boys body. As he crossed them over with his wash cloth he felt a jolt of sensation run straight down his body, straight to Izukus junk.
oh.
He felt his whole face flush at the realization of what just happened. Are Izuku’s nipples really that sensitive? He thought to himself amazed, he knew his own nipples were not like this. He brushed other them again with the foaming wash cloth, the rough surface of the towel sending a wave of pleasure down his body. What the fuck? How did Izuku do anything if his nipples were this sensitive all the time? Katsuki moved on to his abs, thoughts still on the boy's nipples. He wondered if he covered them up so clothes and bumping them didn’t bother him, or maybe they aren’t always this sensitive. Before he could stop his mind from wandering in that direction the thought was already in his head. Could Izuku only finish from touching his nipples? Accompanied by that thought was an image of izuku finishing to katsuki pinching at his nipples. He shook his head fiercely, trying to wipe away whatever the fuck he was just thinking. Why was he acting like a creepy pervert, this shouldn’t be that hard.
Now that the boys whole upper half was clean he knew it was time. Holding his breath he looked down, a small gasp left his lips. His dick was half hard, definitely because of the jolts of pleasure from his nipples being touched. His dick wasn’t as big as Katsukis, to his relief, and not as thick either. It did make sense, Katsuki was taller and bigger than he was , but he was still relieved. But that wasn’t to say Izuku's dick wasn’t perfect. It was so fucking pretty, how is that even possible? Katsuki gulped as he used his arm to lean on the wall, looking down. Izuku’s dick had freckles and a warm red flush to it just like his face did.
Was every part of Izuku’s body sculpted by the gods? Was this even human? Because to Katsuki, with a body like this, he seems fit enough to be an angel himself. How was he so perfect?
The more he thought about izuku’s body the harder Izukus dick got. Oh this was absolutely cruel, katsuki thought to himself, of course this would happen. He should’ve known that this was a bad idea. Just the fact that Izuku’s body was being turned on by looking at himself was insane.
He wanted so badly to touch what was before him but katsuki resisted. If Izuku knew it even got this far he knew he would be as red as a tomato. The only touch he gave it was to quickly clean it with the wash cloth, gritting his teeth at the pleasure that shot through his body. Fuck. Deku was sensitive as fuck. He was so horny it hurt, but fixing this felt like a whole other level of wrong.
He continued to wash the rest of Izuku’s body and then just stood there, letting the water run over his whole body. Erection starting to hurt he was so horny, how was even the water hitting his nipples making him feel good?
If he did this, how was he supposed to look deku in the face? Knowing Deku he probably hadn’t even looked at his out of his privacy. Katsuki groaned at the fact he definitely knew Izuku did not shower, leaving his body covered in germs. He could care less about Izuku doing this in his body, not like he was embarrassed about his junk.
His dick jumped with excitement at the thought of Deku jerking off in his body. Ugh.
He couldn’t remember where it started or when, but the only thing that did it for him was Izuku. It was incredibly fucking embarrassing but he barely ever thought of other things. He didn’t really ever do it in middle school, he had no drive or want to. But once highschool hit, Izuku’s was all he could think about. Maybe it had been his muscle growth, or maybe his growth spurt. Maybe even the fact that he and Izuku were finally kind of normal.
They occasionally tolerate each other for awhile by sparring, studying, and sometimes Izuku would watch him cook. Things have just settled between them, calm. Katsuki always felt like he could just breathe when Izuku was there. Sure, they argued a lot and that nerd finally found his voice, teasing him as much as Katsuki teases Izuku. It was finally normal between them but of course Katsuki had to be some kind of fucking weird pervert and make things awkward. Izuku didn’t know, that was for sure, but he still felt guilty for thinking of him in that way. He couldn’t help it, every inch of Izuku’s skin made Katsukis mouth water with want. Looking down at the boys body, being able to stare at it, touch it, it was driving him insane.
His dick was so hard it hurt, he just stared down, having a war of morals in his mind. Well to be honest, staring at Izuku's erection for this long could be considered just as bad as getting himself off real quick, right? So if he already did the first he might as well do the latter. He couldn’t care less anymore, want and need the only thing left.
The room was full of steam and it was starting to get hard to breathe. Katsuki hand snaked down and wrapped around Izuku’s dick, letting out a hiss at the sheer pleasure going through his body. How much he wished he could do this to Izuku’s body when he was actually in it.
He tried to cum as quickly as possible, feeling guilty about doing this in the first place, but finishing quickly wouldn’t be a hard task when he was so pent up. Once he finally came he let out a heavy sigh, head leaning back onto the wall.
He ended up just washing his body once more before he left the shower, finishing up his nightly routine before he got under his covers.
He needed to get back into his body. At this rate, he was never going to be able to look at deku in the eye again. But it wasn’t his fault. It was Dekus of course, why did he have to be so perfect? he thought to himself before he drifted into sleep peacefully.
Ow, what the fuck. Katsukis eyes shot open, wincing as he sat up. His arms burned as though they were on fire, he left molten lava under his skin. What the fuck is this?
He checked his phone, 4:50 am. Not too bad, and at this point he could never fall back asleep with this pain. He decided to get up and start getting ready. Going to class in Izuku’s body is definitely going to be weird, especially the hands-on training they had today…
Wait, did he have Izuku’s quirk or did he still have his own? He looked down at his arm and squeezed his fist. Like his body knew what to do, green lightning appeared around his fist. With the lighting came the worst pain he had ever felt. So that answered that question. I guess he and Izuku were going to have to be excluded from sparring with their quirks today.
Fuck, his arms hurt so bad it became unbearable. He felt his body start to tense and tighten, his heart rate picking up and his breathing getting shallow. He had a high pain tolerance and even he couldn’t handle this pain. All he felt was sharp, hot needles burning his arms all the way to the socket, and his fingers felt as though they were going to internally melt off of his body.
So he did the only thing he could think of. Call the owner of the body he was in, duh. He grabbed his phone and typed in Izuku’s number 3 times before he got it right. His hands were shaking and he felt as though he had barely any control over them.
After the first few rings he heard his own groggy voice pick up the phone “Hello? Kacchan? Is everything okay, what’s up?” All he could muster in response were short distressed breaths. “Kacchan are you okay?” his voice over the phone turned concerned.
“My body hurts” Katsuki pushed the words out of his mouth, gritting through the pain shooting through him “I feel like I’m on fire.”
“Oh, Kacchan, I’m sorry. I know what this is. I’ll be there in 2 minutes max. Hang in there, okay?” Izuku answered before immediately hanging up.
Just like he said, in less than 2 minutes he was knocking on Katsukis door. Katsuki went to open the door, wincing as he turned the doorknob. As soon as the door opened he saw the concerned expression of his own face before Izuku walked in and herded him back towards the bed.
“Lay down,” Izuku said, pushing Katsuki back, "I'll help you. Just relax as much as you can, okay?” Once Katsuki was down and relaxed he stared up into the ceiling. The pain going through his arms was the only thing he could think of. Absently he obeyed Izuku's orders.
Katsuki felt warm hands touch his right arm, slowly moving up and down, massaging. Then the hands moved to his left arm, then his shoulders and traps. Everywhere Izuku touched, his body calmed. The warmth of Izuku’s hands calmed the raging fire within his body until it was tamed.
It felt like years had passed by the time Izuku stopped, to the point Katsuki almost fell back asleep. But when the hands pulled away, he became acutely aware of the boy next to him. “What was that?” Katsuki said, not knowing what to say at a time like this.
“I have severe nerve damage in my arms from using my quirk.” Izuku started, doing a sheepish shrug, “Usually it just feels like a slight burn or numbness but when I’m stressed my symptoms get worse, like how it felt for you just now. The stress restricts blood flow to nerves and increases infla-“
“So, you’re telling me you’ve been dealing with this the whole time and you didn’t tell anyone?” Katsuki cut him off, sitting up, “How fucking stupid can you be?”
Izuku’s face scrunched a little at the insult, “I don’t need to worry people about something that doesn’t even happen all the time. And heat can soothe it, I’m fine.” He put his hands up in defense.
Izuku got up from his sitting position to stand, and Katsuki followed his lead. “That didn’t feel like no big deal, deku. You need to go to recovery girl or something because this isn’t fucking normal.” Katsuki’s voice grew in volume the more he thought about the situation.
“It’s permanent damage, kacchan! There’s nothing she can do! This is just how I have to live my life.” Izuku matched the volume, his cheeks painted a soft pink from frustration, “I just helped you. I know that hurt like hell, why couldn’t I have gotten a thank you instead of a lecture.” He threw his hands up as he started to walk towards the door.
“Well this is all your fucking fault anyways, why should you get a thank you?!?” Katsuki was now nearly screaming, when he felt something strange happen. He felt like there was an extension of himself reaching forward, reaching towards Izuku. He looked down to see black tendrils reaching for the other boy at a rapid pace. How did I trigger blackwhip?? Katsuki frantically thought to himself, and more importantly, how do I make it stop!!!!
“Whatever, Kacchan.” Izuku said before slamming the door shut behind him. Luckily for Katsuki, the tendrils ran straight into the door before they could get to Izuku and recoiled back to Katsuki.
As Katsuki aggressively laid down, his mind ran miles a minute. What was happening? Why were they reaching for Izuku? Why the fuck is everything so messed up. Why couldn’t he just thank Izuku and go on with his life, why was he like this?!? Katsukis mind was filled with Whys all the way til’ he fell back to sleep.