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It's been four years since Izuku and Katsuki got together, apparently living the perfect life: they have a shared apartment, both in the top 10 only three years after graduation, they're loved by their fans, and they have a cat. They love each other so much.
Izuku reminds Katsuki every day how much he loves him and Katsuki just smiles at him and kisses Izuku stupid. All is perfect. They are happy. Izuku is happy. Katsuki is happy. Except he's not, not really.
Why? Because he's bored. Izuku is boring and the spark of their first years together is long gone. But Katsuki's not /that/ much of an asshole to break up with him before even trying to fix things. He didn't spend half of high school redeeming himself just to be a piece of shit again.
Of course, Izuku knows nothing of the situation, he needs to figure things out alone first. And Katsuki was sure he still loved Deku.
Suddenly, Shouto started to hang out with them more: dinners, hikes, last minutes trips; sometimes other friends joined in, but Shouto was a constant.
And surprisingly, they never bickered much. He couldn't stand IcyHot before, but lately... A few insults sometimes, but that was the norm.
Sometimes Katsuki would catch Shouto staring at him with half-lidded eyes, lost in thoughts. He always sustained the stare for a few seconds before Shouto would look away like nothing happened.
It so happens that, during a time when Katsuki is almost at his limit, he gets called on a mission overseas with Shouto.
Those were not normal looks, he could tell. Shouto was hungry, almost restless, many emotions hidden behind those mismatched eyes. Katsuki could tell because he used to look at Izuku in the same way, and Izuku always responded with a smile, inviting him to come and play.
Katsuki didn't do anything. He never confronted Shouto about it, he just... let it happen. He always not-so-secretly liked the attention, and those of Shouto were eyes that left hot trails of fire on his skin after every gaze.
He liked the shiver he always felt after.
This went on for a while: every time they hung out together, during every patrol, on the last class reunion. It was addicting.
Then it suddenly stopped, when their schedule was a literal hell for an entire month.
They couldn't see each other anymore and Katsuki knew he was screwed when he realized he missed that fucking sensation, that thrill crawling under his skin that felt like a rush of adrenaline.
One day, their agency calls them urgently for a meeting and explains how their help is needed abroad and that a few heroes are required to fly overseas to join a team of extra forces.
Dynamight and Shouto get selected, and Deku is asked to stay in Japan bc he's the strongest hero.
With the joint forces, the mission was easy, and the enemy was defeated in a short time. That left the team with a couple of days to handle the paperwork and relax a bit before returning home.
Bad. The situation was bad because the stares were back and Katsuki hated how relieved he sensed, like a breath of fresh air after a month of nothing.
The thing is, Katsuki never stopped Shouto, but he also never made a move of any sort towards the two-toned coloured hero. His self-control was called 'guilt of breaking Izuku's heart' and it was strong. Or so he thought.
Because that night, when Shouto caught him exiting the hotel elevator, he couldn't help but stare first. And he wasn’t able to stop what came next.
It took half a second for Shouto to read what was hiding behind Katsuki’s eyes. It was surprising seeing some sort of defeat because that’s what Katsuki was feeling: the guilt of having finally surrendered to the desire he thought he could keep locked away.
"IcyHo-"
Too late, Shouto's lips were on his in a heartbeat and they were fucking amazing. Hungry and possessive, Katsuki couldn't do anything but answer with the same hunger.
It was fucking wrong; Katsuki’s cheeks were burning for the shame and the absolute pleasure he was feeling when his lips finally smashed against Shouto’s. He had no right to feel this good.
They quickly exited the elevator, aiming straight to Katsuki’s room a few meters away, never breaking contact.
He was disgusted at how /bad/ he wanted to kiss Shouto, at how starved he was for some physical contact with the redhead.
"IcyHot... Shouto, maybe we shouldn’t-" he said, struggling to open the room with his card, having the back pressed against the door and two hands roaming on his chest didn’t help.
"A bit ah- late for that, don't you- don't you think?" yeah, it was already fucking late to stop anything. He couldn’t explain the fire he was feeling through his veins at every touch, he didn’t feel like that in a long time. Maybe he never did, not even with Deku, and his stomach twisted at that thought, cutting his breath.
He took a mental pause from what they were doing only to realize that they made it all the way from the door through the suite to the bedroom. A sense of panic started to rise when two hands on his shoulder pushed him onto the bed, pointing out the fact that all this was really happening at a really fast pace, and that the bi-coloured head of his hero colleague was between his legs while his hands were pulling down the zipper of his pants.
He realized how his body was moving on autopilot, how he could witness everything like an outside spectator. His mind was struggling against his body, screaming from the inside trying to regain control and stop this situation all at once.
Wrong, wrong, wrong.
“Nghhh, will you shut up?!”
Shouto looked up from what he was doing, perfectly conscious that that order wasn’t for him.
Shame only grew on Katsuki’s face; he fell with his back on the bed trying to focus only on Shouto’s mouth and the magic it was doing. That helped someway because his thoughts were silenced once and for all, deciding to shut down completely.
He woke up at five in the morning with a hell of a headache; it took a while to recognize his room immersed in the dark by the mess of clothes scattered on every surface of the bedroom. A foreign movement at his right startled him and all at once, the memories of hours before hit him with all the heat, the moaning, the touching.
He spent the night with Todoroki, and that wasn’t a fucking dream. Shouto was beside him, sleeping like a baby, body covered in marks and bites, further proof of what happened. He remembered all the sounds of their night of love, all the whispers in the ears, all the kisses and licks and the bruises were right there, staring back at him.
Suddenly he wasn’t feeling well, he was sweating like crazy, completely naked under just a sheet. He got up from the bed - he needed to shower very badly; he could feel the dried-up love juices tightening his skin - when on the way to the bathroom he almost tripped over the tray from the room service.
Oh right. A maid with a cheerful voice knocked at the door at some point, presenting Katsuki with a tray with champagne and chocolate-covered strawberries. He took the thing in a hurry, eager to pick up where he left off and not really caring why someone ordered this for him. He thought that maybe IcyHot was feeling fucking romantic, while finally making his move. They drank the whole bottle in under five minutes, neglecting the sweets.
But now that he was looking at it, he saw it: a small note folded in half and placed in a corner. And when he read it, all the colours drained from his face.
“Hi, Kacchan! Congratulations on completing your mission, you were amazing as always! This is a gift to celebrate your victory, I’ll wait for you at home so I can congratulate you in person~
I love you,
Izuku”
It was like he suddenly exchanged quirks with IcyHot, his blood was boiling and freezing at the same time in his body. He dropped the note to the floor, feeling dizzy and nauseous all together. He ran to the bathroom, barely making it to the toilet before throwing up the entire content of his stomach, which wasn’t much.
And the memories of that night hit again like a truck in a twisted way, seasoned with the guilt and the realization of what he did. He cheated on Deku.
The sensation of nausea and dizziness never left him for all the following day as well: under the shower, at the hotel check-out, on the plane, on the car ride back home, not even when he stopped in front of his – their – apartment’s door.
He opened it as quietly as possible, knowing full well that Deku was home, and entering in silence wouldn’t erase the fact that he had to face him.
And this happened sooner than later because, as soon as he passed the kitchen, his nose was filled with the normally delicious smell of mapo tofu but, because of the state of his stomach, almost caused him to throw up on the floor.
Losing his balance for a moment, he leaned against the wall and the bag slipped from his shoulder making a thud sound hitting the ground.
“Kacchan, you’re back!”
There he was, his boyfriend of four years, his rival of a lifetime, his most important person in the entire world, standing on the threshold of the living room; so happy, so genuinely happy to see him home after a long mission.
“I’m glad you’re home this early, I prepared a lot of food for you, including your favourite- wait, you don’t look okay, you’re pale... how are you feeling, Kacchan? Did something happen while you were away, are you hurt?!”
“NOTHING HAPPENED”
It took a few seconds for him before realising that he just shouted in his boyfriend’s face.
“I mean- I’m fine! I just have a stomach ache... sorry if I screamed, didn’t mean to.”
“I-it’s okay, Kacchan! It’s understandable if you’re not feeling well. Sit down for a bit, it’s alright”
He let Izuku take his hand to guide him to the couch to lie down. He closed his eyes and when he opened them again an hour passed and Deku was sitting next to him with a beautiful smile on his face – the one that made Katsuki fall for him – and a bowl of hot chicken soup in his hands.
“Here, this will help. Sit straight and drink”
Katsuki was actually starving but he couldn’t bring himself to eat even one bite.
“If you’re feeling better, do you mind telling me about your mission?”
“It was nothing out of the ordinary... we got there, kicked some villains’ ass and boom, victory”
“You said you got some time off after the mission, right? Did you have fun with Shouto?”
And there Katsuki almost choked to death when the soup he was trying to eat chose the wrong canal.
“Careful! Here, take a napkin!”
He grabbed it and between one cough and another he managed to ask “W-why would I have fun with IcyHot out of all people?!”
“I’m sorry, I thought you two started to finally get along lately, guess I was wrong ahah”
Wrong
“Oh, how did you like my surprise?”
“It was... unexpected.”
“Eheh right, that’s what I wanted! I chose chocolate-covered strawberries because we ate them on one of my favourite dates! But I hope that wasn’t the thing that made your stomach upset”
“I-it was probably what I ate during the flight, don’t worry too much about it”
“Alright, I’ll let you rest for another bit. I’m glad you came back safe.”
He leaned forward and kissed Katsuki’s forehead.
“I love you, Kacchan”
He brushed his blonde hair a couple of times, then exited the room smiling after dimming the living room lights.
He couldn’t lie to himself anymore, now he was certain. He faced the truth: he didn't love Izuku anymore. He didn't for a long time.
A few months earlier
"Seduce him."
"What?"
"You heard me."
"Yes, but I don’t understand"
"I saw the way he looks at you, he may not be aware of it but I sure am. And I know you are dying to put your hands on my boyfriend, do you?"
"It was never a secret for you"
"So, seduce him."
"He's still your boyfriend though"
"Yeah, well... you can have him now. He can say it how many times he wants but I know he's lying when he says he loves me."
"If I can have my way with him... does that mean you're gonna break up with him?"
"Oh no, that's the fun part. He has to believe he's doing it behind my back the whole time. I want to make him suffer for lying to my face like that."
"Why do you have to make things complicated. I thought you cared about him no matter what?"
"Because I'm sick of being the one to constantly ask to be loved! I’ve spent my entire life chasing after him, telling him how great he was, how he was my everything, I fucking deserve it! And if Kacchan doesn't want me, he won't have the pleasure to enjoy his new relationship without feeling a guilt so deep he won’t be able to sleep peacefully again for a long time.”
“That’s... a lot. Don’t you think you’re going too far?”
“I don’t care. And neither do you. You can have my old toy. I know it doesn’t matter to you if it's broken, as long as it's yours."