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When Izuku entered the classroom, the first thing he noticed was that Aizawa’s desk was unusually tidy, devoid of the usual pens or exam papers that cluttered the wooden surface. The second thing he noticed was the scribbles on the board that read Sex Education.
Once everyone settled into their seats, Aizawa leaned against his desk, crossing his legs. “As you probably figured, we're having a… different class today. According to the principal, high-schoolers need to be educated on sex.”
“Seriously?” Katsuki gloated, kicking his chair back to tilt it onto its hind legs. “That’s a real waste of time.”
An odd shadow passed over Aizawa’s face. “Bakugou, come up here.”
“Huh? For what?”
“Do as I say.”
Katsuki let out a huff but hauled himself out of his chair and ambled up to the desk. Everything moved so quickly that Izuku barely had time to register it; one moment Katsuki was glaring at Aizawa, and the next he was pinned down with his chest on the desk, capture scarf wrapped tight around his limbs. Katsuki grunted, wriggling to break free from the hold, but Aizawa tightened the scarf until he couldn’t move at all.
"Oi, Sensei! What the f–"
Another section of capture tape slammed against Katsuki's open mouth, forcing his teeth apart so he couldn't talk. His muffled yell was cut off by another layer of bandages. Bright sparks exploded from his hands a second before Aizawa's eyes flared red and his hair rose like it was underwater, instantly cutting off Katsuki's quirk.
"There are conventional teaching materials, obviously," Aizawa said casually. "But I thought a hands-on demonstration would be better."
Kaminari spoke first, his tone disbelieving. "You don't mean…"
Izuku's mind was whirring, his gaze fixed on Katsuki, wriggling like a fish in a net with his hips twisting in a way that was transfixing. An uncomfortable heat tugged at Izuku's gut, prickles coursing from the base of his skull down his spine.
"If you're ready, we can get started," Aizawa said, hooking a hand in the waistband of Katsuki's school pants. Katsuki let out a screech as his pants and boxers were yanked down in a fell swoop, pooling around his kicking ankles. "I assume all the girls have seen a male body before."
Yaoyorozu's jaw had fallen ajar. "S-sensei!"
Aizawa trailed his hand over the swell of Katsuki's ass, tracing the expanse of pale, smooth flesh. The shivers along Izuku's spine had erupted all over his body, his pants tightening. Though the angle wasn't great, Izuku could make out a hint of Katsuki's dick pushed against the blunt edge of the desk, his balls dangling between his thighs.
"I assume you're all versed on vaginal sex. However, when it comes to anal, there are a few extra considerations. If you don't prepare properly, you can cause a lot of discomfort. Watch."
Aizawa dipped a thumb into the tight, pink furl between Katsuki's asscheeks, making him choke on a yell. "See? It's especially hard for virgins to take it without preparation." He cast a casual glance at Katsuki. "Now, it's a myth that you can tell whether someone is a virgin from the state of their genitals. However, Bakugou's behavior is a dead giveaway. With his quirk, it's unlikely that he's even experienced an orgasm."
"Is that true?" Kaminari crowed, finding his voice. "Bakugou's never jerked off?"
"That explains why he's always so wound up all the time," Ashido called out. "Sensei, you should help him out!"
"This is purely for educational purposes," Aizawa informed her as he reached over to open the desk drawer with one hand, pulling out a purple bottle. "Since Bakugou is always so adamant that he's the best, I figured everyone would want to see whether he's good at taking cock, too."
Katsuki's eyes widened. The prospect of him flailing on their teacher's cock had Izuku gripping the edge of his desk with whitened knuckles, leaning forward as Aizawa poured the lube over his fingers.
Izuku had fantasized of Katsuki more times than he could count, cock hard in his wet fist as he thrust his hips up, eyes clenched shut so he could imagine it was Katsuki around him. Even if he wanted to fuck him more than anything, he couldn't deny that watching him get fucked sounded like something straight out of his fantasies, too.
"I'll let you talk if you behave," Aizawa warned, releasing the capture scarf fastened around Katsuki's mouth. “Be good.”
Instantly, Katsuki started yelling. "I'll kill you! Get the fuck off me, you old pervert–"
Ignoring him, Aizawa cupped one of Katsuki's asscheeks and pulled it aside to reveal his twitching hole. "Stay still, or I'll make it hurt."
"Fuck, no! I'm gonna kill–"
Aizawa pushed a thick finger inside Katsuki, making him let out a thick groan, then looked back at the class. "I would recommend starting with fingering, though you could also try rimming if you'd prefer."
Izuku could imagine it easily; Katsuki lying on his bed, moaning and rocking his hips back against Izuku's mouth, begging for his tongue, his lips, crying out his name. Katsuki wouldn't wriggle away from him like he was trying to do from Aizawa, wouldn't scream curses and try sparking explosions that wouldn't come under Erasure.
"Stop going easy on him, Sensei!” Kirishima hollered. "Bakugou's so manly, he deserves for you to give him a challenge.”
"Shut the fuck up! I don't want more," Katsuki screeched, trying to kick Aizawa's legs. The capture scarf tightened around his knees so he couldn’t do anything except wiggle his hips, which just made the scene lewder. "Get your finger out of me! You're fucking disgusting!"
The words came out of Izuku's mouth before he could stop himself. "I know you can take it, Kacchan. You're the best."
"Shut up, shitty Deku!"
"He's just being supportive," Hagakure scolded, her uniform dancing like she was jumping up and down. "You should be more appreciative. You're about to get fucked by an expert."
"I don't want that," Katsuki shot back, thrashing around. "Get off me!"
Aizawa just pushed another finger into him, forcing a loud cry from him. Izuku couldn't help but let out a soft moan at the sound, reaching down to shove his hand into his pants, rolling his hips against his rough palm. It wasn't slick enough, but the burning friction felt good, his scars rubbing against his sensitive cock.
He looked back up just in time to meet Katsuki's shocked eyes, flickering down to where Izuku’s hand was obviously wrapped around his dick.
"Are you jerking off?" Katsuki said, stunned, as if he momentarily forgot that his teacher's fingers were buried in his ass.
Izuku's face warmed. It was embarrassing to be called out for jerking off in front of the whole class, though it wasn't enough to get him to stop. "I'm sorry. You're really hot, I can't help it."
"You're a real pervert," he hissed, but his cock was hard now, precome smearing over the desk. It just made Izuku want him even more.
"That's enough," Aizawa said, eyebrows furrowed into a frown. "I was going easy on you, but you're testing my patience. Obviously, you're ready to be fucked."
Fear flashed in Katsuki's eyes, along with something that Izuku knew intimately well. He could tell it from the way Katsuki subtly rolled his hips against the desk to steal stimulation on his leaking cock, how he stopped struggling as fiercely as he was at the start. Arousal.
Aizawa tugged on the bandages just enough to force Katsuki's back into an arch. "Take a deep breath."
"Stop," Katsuki demanded, though he wasn't putting in as much effort to escape. "Don't, Sensei–"
He gripped Katsuki's hips and pulled him back onto his cock, sheathing himself inside Katsuki's ass in one swift motion. Katsuki let out a pained yell, but Aizawa just squeezed his hips tighter and started fucking him, forcing his body across the desk with each merciless thrust.
"Stop," Katsuki begged, squeezing his eyes shut. "Let me go."
Aizawa was unfazed, turning his head to address the class as his hips continued snapping forward without pause. "If you go too fast or don't do enough prep, you'll hurt your partner. For example, Bakugou’s obviously in pain. However, in this case, it's okay because this is a class." He drove his cock deeper into Katsuki with a harsh thrust that made him cry out louder.
"And Bakugou's a little bitch that needs to be put in his place," Mineta added, grinning. "Look at his tits and his ass! He's practically a girl."
Aizawa shot him a withering glare. "This isn't a punishment. I already told you, Bakugou is one of the best students in this class. I chose him because I knew he could take it." He squeezed Katsuki's asscheeks. "Still, you're not all wrong. This ass was begging to be fucked. Isn't that right, Bakugou?"
Katsuki's face was blotchy with heat, a red flush crawling down his back. "It's too–much–"
Aizawa didn't listen, yanking on Katsuki's hips to fuck into him harder, punching high-pitched cries from his mouth. Izuku's hand sped up on his dick, biting back low moans as the sight of his childhood friend getting fucked in the ass fueled the pleasure coursing through his groin.
"Fuck him harder," Hagakure demanded, prancing out of her seat again. "He can take it, Sensei!"
"I'm so jealous," Ashido sighed, her gaze tinted with admiration. "They're both so hot."
Izuku felt a flash of jealousy as well. He had loved Katsuki all his life, so it almost seemed unfair that Aizawa got to fuck him after knowing him for just under two years. Still, this was a sex education class. He was just being a good teacher.
"Another lesson," Aizawa declared, gripping Katsuki’s hips tightly enough that his fingers left angry red bruises in his skin. “When fucking a man, you should try to stimulate the prostate. It's about two to four inches in, so for direct stimulation I would advise using your fingers or a toy—” He drew his hand back and slapped Katsuki's ass, hard, making him yelp. "But some need a cock in their ass to shut them up. Isn't that right?"
His face was scarlet, his breath coming in staccato pants. "Shut–up–"
"I asked you a question." He slapped Bakugou's ass again, leaving a flaming handprint. "Do you like having your ass fucked?"
"N-no—"
"Don't lie." His next thrust pulled a lewd, drawn out moan from Katsuki's lips. "I think you like it. You like showing off how good you are at taking cock. You'd be a good cocksucker, too, with that big mouth."
Katsuki let out a groan, dropping his forehead to the desk, drool dripping onto the wood. "Fuck, Sensei."
"Maybe we could ask Midoriya to help." He shot a look at Izuku, who tried not to show his excitement. The idea of fucking Katsuki’s mouth, swollen lips stretching around his cock, had him ready to blow. "Clearly, he's enjoying this."
"Damn it–you're insane," Katsuki forced out through gritted teeth, tilting his head enough to glare at Izuku under tangled locks of hair. “I'm–ah–not sucking stupid Deku's dick."
"Why not? You're already letting your teacher fuck you."
"I'm not–" A strangled moan broke up the panted words. "Not letting you do anything."
"Is that so?" Aizawa's tone was casual. "I lifted Erasure the moment I started fucking you. You sure don't seem in a hurry to break free."
A few sparks crackled across Katsuki's palms, but he just pressed his cheek harder against the desk, sweat-matted hair obscuring his face. Izuku's cock was hot and heavy in his hand, his strokes speeding up at the sight of Katsuki taking it, moaning as he was fucked roughly.
Aizawa's expression turned triumphant. "See? I knew it."
"Fuck–ah–fuck you."
“Actually, I’m fucking you,” he said, unbothered. “And you know what? It’s damn good. I’m almost jealous that your classmates get this whenever they want.”
“I’m not—shit—fucking anyone.”
He raised an eyebrow. “Do you really expect me to believe that you wouldn’t spread your legs for Todoroki or Kirishima?” He leaned over again so his lips almost brushed Katsuki’s ear. “I know you, Bakugou. You just want someone to tell you how good you are. You fucking live for that praise, but you’ll take being called a slut, too, if it means you can submit to someone the way you crave. Luckily for you, I know how to give you what you want.”
Katsuki let out a sound that could only be described as a whimper, twisting his hips back as if trying to take Aizawa’s cock deeper. “Sensei…”
“What is it?” Aizawa ran a soothing hand over one of Katsuki’s asscheeks. “Tell me what you want.”
His voice was weak. “Fuck me harder.”
“Good boy.” A grin broke out over Aizawa’s face as he sped up his pace, his hips slamming against Katsuki’s with a wet clap every time he fucked in. His gaze was fixed on his cock disappearing into Katsuki’s ass, so focused that he didn’t look away even when he raised his voice to address the class. “And that’s how you get a brat to behave.”
The class broke out into applause, and the situation was so absurdly funny that Izuku would have laughed if he wasn’t coming into his palm with a broken moan, gripping his shaft and pumping as sticky liquid spattered over his palm.
“That was so cool, Sensei,” Uraraka declared, face bright with enthusiasm.
“How does it feel to make Bakugou your bitch?” Mineta cheered. Izuku whipped around to glare at him; no one got to call Kacchan a bitch.
“He’s not a bitch,” Aizawa corrected sternly, echoing Izuku’s thoughts. “Give your classmate the respect he deserves for helping you with your sex education. He did so well—didn’t you, Bakugou? I think you deserve a reward.”
All Izuku could do was stare, entranced, while Katsuki came apart, gasping and trembling as he came hard all over the desk. Aizawa gave him a few more thrusts before he pulled out and came onto Katsuki’s back, painting sticky white stripes over his sweat-drenched skin.
Katsuki stayed there even when Aizawa pulled out of him, slumped over the desk, his breathing hard and ragged.
“Lesson over,” Aizawa said calmly, leaning against the blackboard. “Any questions?”
Izuku’s hand shot up.
“Midoriya?”
His voice was determined. “Can I have a turn?”
The classroom erupted into chaos, yelling and arguing over who got to have a turn with Katsuki next. When Izuku inevitably won the brawl, Katsuki almost looked pleased, shifting his hips to make himself more comfortable while a thrilled Izuku took his place behind him.
Well. It looked like Aizawa did them a favor.