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From a young age, Izuku had been told his curiosity would be the death of him. Sitting in the center of a summoning circle surrounded by black candles and the copper tang of his own blood, he was inclined to believe that.
That didn’t stop him from digging the edge of a blade across the back of his forearm, blood viscous and hot welling up along the length of the new cut. It slid down his skin and dropped against the concrete floor, swallowed up by the porous surface. A thick, leatherbound book lay open on his lap, an incantation written in rust-colored sigils taking up both of the vellum pages. Before he could lose his nerve, Izuku began to read, tongue shaping around the unfamiliar sounds with careful precision.
The sharp scent of ozone flooded Izuku’s nose halfway through, his curly hair standing up on end as the cool air sparked against his skin. He continued, heartbeat a thunderous drumming on the inside of his breastbone as if demanding release. As the final word dropped from between his lips, the flames of his candles flared up toward the ceiling in a wild release of magic, lighting up the room in brilliant red. Just as abruptly they snuffed out, leaving behind the sullen, greenish glow of his magic suffusing the summoning circle.
He was not alone.
“And what foolish little witch has summoned me now?” A voice like smoke and ash and burning curled through the silence, coming from nowhere and everywhere at once. Izuku shivered, acutely aware that one wrong move would leave him dead without anything to gain from it.
“Deku,” Izuku offered, proud when his voice didn’t shudder. The creature laughed, harsh but amused, and the shadows that filled the room coalesced, dense as smoke. Eventually they settled into the shape of a tall, broad shouldered man crouched just inches from Izuku, grin a sharp slash across a cruelly handsome face. Eyes, red like the embers at the center of a burning building, regarded Izuku with dark humor.
“Deku, huh?” He reached out a large hand, fingers stained black to the second knuckle and tipped pitch dark nails sharp as talons. He stopped just short of the smaller circle etched around Izuku and his smile widened, pointed teeth on full display. “You’re clever about your idiocy, little witch. ”
“I’m n-not an idiot.” Izuku struggled to keep his gaze up, to maintain eye contact with the demon as he became acutely aware that he wore the form of a man but none of the trappings. Tattoos in a spiky, unfamiliar language sketched across toned muscle and despite himself, Izuku’s line of sight dipped to follow them. Heat flared to life in his cheeks and it took every ounce of willpower he had not to hide his face behind his hands.
He was…ah…well endowed and the chuckle that rumbled in the demon’s chest showed he knew exactly where Izuku’s eyes and thoughts had wandered.
“See something you like?” He spread his knees wider and Izuku’s eyes once again fell between the demon’s thighs, drawn as if by a magnet to the flaccid, girthy length of his cock where it nested in a thatch of coarse, blond curls. The train of Izuku’s thoughts derailed and crashed spectacularly as he imagined what that cock would feel like inside of him; he was horrified when his own pants tightened.
What the hell was wrong with him?
“I didn’t do all this—“ Izuku gestured at the complicated summoning circle around him with hands that barely shook. The flames of his candles slowly sputtered to life unprompted, bringing more light into the bare room. They illuminated the folded over carpet that Izuku had carefully ripped up to make space, the bookshelf overfull and close to buckling beneath the weight of his journals and tomes, a desk just as burdened and a bed, pushed up against the far wall as an afterthought. When he swept his hands back, his voice lost its steam. “—for, um. That?”
“You sure? Sounds like your priorities may have shifted.”
“No!” Izuku shot up on his knees, barely catching his book before it tumbled off his lap and scuffed his protective circle. His already racing heart skyrocketed and he leaned forward as far as he dared, staring the demon straight in the eye. “I want to learn from you. The magic I have learned isn’t very powerful and books on, well, anything even remotely legitimate are so few and hard to get that I’ve started writing my own spells but they don’t work half as often as they do and I’m running out of resources—“
The demon placed a finger over Izuku’s mouth, his pointed nail digging into the base of Izuku’s nose. The pain shocked him out of his rambling and the demon’s proximity dumped cold water over his heated skin, fear settling into the joints of his bones. The demon watched him with a smug smile as Izuku dropped back down onto his ass, numb. “How?”
“You missed a sigil here.” He tapped the space near Izuku’s ankle. “You needed a binding symbol to stabilize the circuit of magic through your protective circle. Even without it, this would keep you safe from minor demons.”
The demon dropped from his crouch onto his knees and crawled forward, pushing Izuku back until he lay flat on the ground, dwarfed beneath the demon’s looming body. “Unlucky for you, Deku, I’m not a minor demon.”
“Who are you?”
He thought about it for a moment. “Guess you can call me Katsuki. Think you can remember that?”
“Yes?”
“Good. I want to hear you screaming it when I have you impaled on my cock.”
“What?!” His voice squeaked as heat chased away the fear in a wave, his face and chest smoldering with an embarrassed flush. Katsuki laughed at him, hot breath ghosting across Izuku’s cheeks.
“I’m feeling generous. You want a teacher? Fine, I’ll help you out. You aren’t completely useless with ritual magic and I can work with that.” Despite his embarrassment, Izuku listened carefully, aware enough that Katsuki was offering him a pact. So he held his breath, biting down on his lower lip to keep from interrupting. He didn’t miss the sultry turn Katsuki’s grin took as he continued. “In exchange I get that horny little soul of yours and exclusive rights to your life energy.”
Izuku sputtered. He always knew his soul was on the table as payment, but he had banked on the opportunity to negotiate. This was a heftier price than he had bargained for and he had nothing better to offer.
“My life energy?” Izuku asked, stalling as he tried to think of anything he could trade in exchange. Anything at all.
“Lots of ways to give it, but let’s be honest, you’ve made your interest clear.” Katsuki slid a hand down the length of Izuku’s body and cupped his crotch, squeezing hard enough to hurt. Izuku choked back a moan, tears prickling at the corners of his eyes as pleasure zinged up the line of his spine. “What do you say, we got a deal, little witch?"
“I don’t—ah— know…” Izuku squirmed as Katsuki kneaded his palm into his growing erection, brain short circuiting as the stimulation became too much for him to think clearly.
“You’re inside this circle with me, Deku. I can just take what I want from you and leave you for dead,” Katsuki said with casual cruelty. The thought should’ve been sobering, and it was, but not enough to give Izuku the space he needed to spin this in his favor. He was fucked. “Sure, you’d get to keep your soul, but I get the feeling that’s poor consolation for you. Why don’t I give you until the count of five to make a decision, seem fair?”
“No!” Izuku shouted, or tried to, but his protest broke on a moan as his hips bucked up of their own accord, chasing the pressure of Katsuki’s hand.
“Five.”
He didn’t know the consequences of losing his soul. The lore he’d managed to dig up simply consisted of dire warnings to never, ever sell your soul to a demon. Nothing else. Nothing useful that he could extrapolate from. “I just need a moment to—”
“Four.”
If he didn’t give his soul up he would die here today from a stupid mistake. One sigil in a slew of hundreds—but had that been the only mistake? He had never meant to summon anything stronger than an imp and yet he’d ended up with Katsuki, something far stronger. “Please just let me—”
“Three.”
He had never read an account of someone getting their soul back. Chances were he’d never figure out if it were possible himself. Death might be worth keeping it, but in truth, Izuku wasn’t ready to die.
“Two.”
There was too much Izuku wanted to know, too much he wanted to learn. For better or for worse, if his soul was the price he had to pay to continue his research, he was ready to pay it. He would deal with the consequences as they came.
“One. Time’s up, Deku. We gotta deal?” Finally, Katsuki removed his hand from Izuku, placing it back by his head so that he could crowd into Izuku’s space. The lack of warmth and stimulation did little to bring clarity to his thoughts and he’d never know if a clearer head would have resulted in a different decision.
Probably not.
“Yes, okay! Deal.”
“Perfect.” That was all the warning Izuku got before Katsuki sealed his mouth over his, sharp teeth nipping at Izuku’s bottom lip hard enough to draw blood. A long tongue invaded his mouth when he gasped, choking off his breath even as it brought the harsh tang of copper with it. Izuku brought his hands up, wrapping his arms around Katsuki’s neck to hold on for dear life as he was wholly consumed. Pain split across his forearm and his grip slid as the cut he’d made earlier reopened and wept freely.
Izuku’s lungs burned when Katsuki finally broke the kiss, the rush of air he sucked in stinging as he filled his lungs with greedy mouthfuls that tasted like blood and wood smoke. His vision swam when he opened his eyes, taking a long moment to focus on Katsuki above him.
His heart stuttered, breath stalling.
Ridged obsidian horns curled from the sides of Katsuki’s head like those of a ram, ornate golden chain imbedded in the intricate texture. Eyes, once brilliant and red, bled black from corner to corner with a narrow, snake-like slash of the red remaining; the markings that had decorated his skin cracked with an orange glow reminiscent of magma. Blood coated the back of his neck, dripping down his chest from where Izuku’s arm had slid against him. He still held a human shape, but there was no part of Izuku that could deny that a Greater Demon had him pinned to the ground at his mercy.
“Oh.”
Katsuki leered at him. “Oh, indeed. Tell me your real name, you masochistic pervert.”
Izuku’s cheeks burned. “I-Izuku Midoriya.”
“Good boy.” Katsuki sat up on his knees, giving Izuku a clear view of his cock where it hung semi-erect between strong thighs. The color had deepened to a rich, purplish red that darkened to the same dusky black at the base that stained his fingers; golden piercings lined the underside in a neat row, a complement to the natural ridges along the top, all terminating in a flared head. It was monstrous, big enough that Izuku would need two hands to wrap around it and it wasn’t even fully erect.
“I’m going to mark you,” Katsuki said as he dug his nails into the collar of Izuku’s shirt, slicing through the fabric as if it was water; his trousers and underpants received the same treatment and everything fell away from Izuku in tatters. Now exposed completely, the shame and embarrassment from before returned to paint his chest in a brilliant flush. Katsuki placed his hand on his sternum over his heart and when Izuku met his eyes, Katsuki offered him a wicked grin. “And it’s going to hurt.”
Something long and flexible and warm slithered along Izuku’s side, sliding over his hip to coil around his dick just as the hand on his chest lit up like live fire, branding Katsuki’s handprint deep into Izuku’s skin.
He screamed soundlessly, arching off the floor even as the thing around his cock stroked and pulled and squeezed, flooding pleasure in with the agony until Izuku couldn’t separate the two. The smell of cooking flesh pervaded his nose, the hiss of his skin burning seared into his brain. He gasped and sobbed, tears pouring down the sides of his face to soak his hair; he grasped at Katsuki’s wrist with both hands, but it didn’t budge an inch. So he held on for dear life as the opposing sensations became his entire world.
The pleasure-pain wracked through him with unexpected force as it reached its crescendo and he came without a sound, jerking hard as cum splashed across his stomach and his vision whited out.
Eventually Katsuki removed his hand from Izuku’s chest and the pain abated to a dull throb in time with his heartbeat.
“Don’t you dare pass out on me now, Deku, we’re only just getting started.” The weight of Katsuki’s cock against Izuku’s thigh, heavy and nearly the length of Izuku’s forearm, punctuated his statement. A long tongue laved across Izuku’s cheek from chin to temple before hot lips sealed over Izuku’s in a possessive kiss. A heady rush of blood not his own flooded his mouth; the warmth of it traveled down his throat. When he swallowed, the throbbing of his chest disappearing entirely as the mouthful of blood left him intoxicated. He returned the kiss as best he could, chasing the flavor of Katsuki back into his mouth, nicking his tongue on his sharp teeth.
Katsuki broke away, lips rouged with both of their blood. He licked the mess away in a slow, sensual swipe, never breaking eye contact with Izuku. Izuku swallowed, throat clicking.
“Let’s get a look at that ass,” Katsuki said and Izuku found himself flipped over, forced on his hands and knees in one deft motion. When Katsuki placed a hand in the middle of Izuku’s back to push him down, he resisted, all too aware of the burn taking up half his chest. He collapsed beneath Katsuki’s strength all the same, no match for a demon twice his size, and braced himself for the pain.
It never came.
“What did you do?” Izuku asked, awed as he touched the edge of the raised surface of his brand, hands barely fitting beneath his chest and the concrete floor. The cut along his forearm felt old, flesh stitched together beneath itchy new skin. “I’m healed. Does that mean your blood has healing properties? Can all demons do that? Or is it part of the magic of our deal? Does it have to be fresh blood or can it mmph—“
That warm, flexible length from before shoved between Izuku’s teeth, gagging him. The realization that it was a tail, that Katsuki had a tail, came as Katsuki draped himself over Izuku’s back and whispered into his ear. “Why don’t we find a better use for that pretty little mouth of yours?”
He nipped Izuku’s ear and settled his mouth on the back of his neck. Izuku keened, lips stretched uncomfortably around the ridged length of Katsuki’s tail as it fucked in and out of his mouth, stretching his jaw until it popped. The blunt end nudged the back of his throat, choking him as it slithered down. A large hand gripped his cock, stroking in time with the tail in his mouth, working him back up to full arousal in just a few short jerks. Drool pooled down his chin, coating the tail and his arms as he gagged on it. When Katsuki dug his teeth into the flesh of Izuku’s shoulder, he moaned, broken and muffled. If not for the tight grip of Katsuki’s fingers around his cock, he would have come a second time just from the pain alone.
Katsuki’s tail slid out of Izuku’s mouth as he dislodged his teeth from his neck. He squeezed Izuku’s cock once more, tight and painful, before letting go. The sudden loss of touch left Izuku bereft.
“No, please ,” Izuku sobbed, unsure of what he begged for but desperate for it nonetheless. Katsuki laughed at him again, the sound rich and condescending.
“You’re being awfully greedy, Izuku.” His given name sounded like sin dripping from Katsuki’s lips. “If you think I’m letting you come again until I’m buried so deep in your ass you feel my cock in your throat, you’ve got another thing coming.”
Izuku combusted, imagination running wild with the visual Katsuki’s smoky voice painted for him. He squirmed, shifting on his arms in dumb defiance, but before he could even think of reaching back to jerk himself off, Katsuki’s tail made a reappearance, wrapping around the root of him like a living cockring. A second later his ass screamed with pain, following the loud smack of Katsuki’s open hand against him.
“What did I just say, you shitty little pervert?”
Izuku couldn’t help it, he moaned, words going straight to the center of him.
“You really are a masochistic freak, aren’t you?” Katsuki said, sounding almost awed. “You say you summoned me to teach you, but I think you just wanted your ass fucked raw.”
“N-no, I want—“
“Don’t need to justify yourself to me, Deku. I’m more than happy to feed off every shameful desire you’ve got crammed into that filthy mind of yours.” Katsuki smacked him again, chasing the pain with the scrape of his teeth across his ass. “Let’s start with seeing how many times I can get you to scream.”
Katsuki split his ass open and slid his serpentine tongue between the cleft of his cheeks, tasting Izuku from the root of his balls to the base of his spine in one languid swipe. Izuku buried his face in his folded arms, but it wasn’t enough to muffle the garbled cry that crawled out of his throat. Katsuki teased him mercilessly, the pinprick sting of his nails digging into his ass juxtaposing the slick pleasure of his undulating tongue as he swirled over and around Izuku’s entrance but never quite pressing in. When he finally did, Izuku jerked back against him with another shout, squirming as Katsuki’s tongue writhed impossibly deep, thrusting in and out in torturously slow strokes. His voice rose with each passing moment, mindless cries warring with the obscene slurp of Katsuki taking him apart.
His cock ached where it hung neglected between his spread legs, precome drooling from the head to splash against the concrete. The tight coil of Katsuki’s tail around the base was the only thing that kept him from coming untouched.
When Katsuki finally pulled out, Izuku couldn’t swallow his whimpered protest; the chuckle that rumbled from Katsuki’s chest would have mortified him if he had any brain matter left to spare for such things. As it were, his body trembled with impossible need, arms barely holding him in place as Katsuki replaced his tongue with two slippery, thick fingers.
“There you go,” Katsuki said, the burr of a laugh still rich in his voice as he pumped his fingers in and out. Izuku’s eyes watered as the pleasure that had pooled molten and overwhelming at the base of his spine cooled at the leisurely pace Katsuki set. “Show me how much you can take.”
A third finger pressed in next to the other two, the stretch painful. The fourth finger hurt. Even as something wet slid down his thighs and coated his insides to ease in Katsuki's fingers, it hurt. Tears poured freely down his cheeks as his body adjusted, breath hiccuping as he tried not to sob.
"Do you want to give up already?” Katsuki mocked, shoving his fingers in pointedly. Izuku groaned. He slipped in and out of coherence as the pain once again sparked with pleasure every time Katsuki drove his fingers in, thumb a promise and a threat against the abused ring of his entrance. “I didn’t take you for a quitter, Deku.”
“‘m not,” Izuku slurred indignantly, tongue thick as he tried to form words. “Can take it.”
“Well, in that case…” The press of Katsuki’s thumb in alongside his other four fingers was excruciating; sensation all consuming and pervasive in a way Izuku barely comprehended. His throat stung, mouth dry; it took him a long moment to realize it was because he’d started screaming into the fold of his arms. He could barely breathe. He wanted to escape. He wanted more.
And then Katsuki’s hand breached him fully to the wrist.
“Would you look at that, you can take it.”
“Told you.” Izuku sounded wrecked even to his own ears.
“Cheeky witch.” Katsuki pushed his hand in further, feeding inch by unbearable inch of his forearm into Izuku until Izuku felt every organ shift to accommodate the intrusion. He sat like that for a long moment, arm nearly swallowed to the elbow by Izuku’s ass. It gave Izuku the chance to breathe, concentrating on relaxing just enough for his body to adjust. A difficult task when Katsuki apparently found himself in a chatty mood, free hand tracing the rim of Izuku’s entrance. “Who’d have thought the first witch to summon me in a century would be such a filthy, fucking whore. I lucked out with you, Deku. Taking my fist so nicely, it’s like you were made for it. I can’t wait to get my cock inside of you, I can’t wait to ruin you.”
He pulled back and thrust in hard, punching a wail out of Izuku. His knees buckled but Katsuki caught him before he collapsed.
“Would you like that, Deku? Would you like me to ruin you for every other useless dick you bend yourself over for?”
“Yes, please, ” Izuku begged, clenching down on Katsuki’s forearm in dreadful anticipation.
“My pleasure.” He slowly removed his arm from Izuku, the process smooth until his knuckles caught on the ring of Izuku’s entrance. When he drew completely free of Izuku, the emptiness inside him swallowed him whole. He needed Katsuki back inside, need to be filled up and abused, fucked until he forgot his own name.
There wasn’t a warning when Katsuki obliged him.
Izuku shouted as his face scuffed the concrete floor when his grasping fingers slipped on a patch of dried wax, arms unable to hold him up as Katsuki thrust into him with brutal strength. His stomach distended with each push in, insides shifting to make space. It hurt in the best way possible, all encompassing and overwhelming, bleeding into a pleasure that knocked him blind and stole his voice.
“Fuck, yes, take it.” Katsuki set a punishing pace, taking his pleasure from Izuku’s body without regard for Izuku’s own; he tried to hold on for dear life but each thrust forward scraped him along the concrete, his balance shot as he was used completely. He sobbed, or maybe he never stopped crying, as the pleasure built and built and built, pushing him to the edge and then past it without release. Katsuki bore him nearly flat to the ground, his weight oppressive against Izuku’s back as he railed him blind.
“Please,” Izuku gasped. “Please, please, please!”
“What did I say I wanted to hear?” Katsuki slowed his pace so that he could hiss into Izuku’s ear. "When I had you impaled on—"
“Katsuki!” Izuku screamed it, not waiting for him to finish, too desperate for release to worry about offending him. ”Katsuki! Please let me come!”
“Very good.” Katsuki’s tail uncoiled from around his cock and was replaced by his hand, nearly enveloping the length of him whole in the tight squeeze of his long fingers. He began to fuck into Izuku again, deep and filthy but Izuku didn’t notice as his orgasm hit him like a train. Pleasure, knife-sharp, dug into his belly and spread out until he saw stars, toes curling and teeth going numb. Cum saturated the narrow space between his hips and the floor, coating his lower belly and Katsuki’s fingers.
The world blacked out.
He woke again only moments later as Katsuki grunted above him with an arrhythmic stuttering of his hips, warmth flooding Izuku’s inside until his stomach tightened uncomfortably and the sensation of being too full had him shifting under Katsuki to escape it. Katsuki laughed at him, wrapping an arm beneath his chest so that he could lift him up and settle him on his lap, back to chest. His cock remained inside, trapping the obscene amount of cum inside him.
“You look so good with me inside you,” he rumbled into Izuku’s neck, tongue lapping over the bite mark until it smarted. He placed a hand on Izuku’s stomach and pressed it into the bulge distending the tight skin. Izuku whined as the cum trapped inside him shifted and slid around Katsuki’s softening cock, that feeling of being overfull intensifying as he kneaded and pet Izuku with a teasing hand. “Even better with my mark on your chest.”
Izuku touched the shiny pink of Katsuki’s handprint, his own hand dwarfed by the size of it. In the center it had begun to turn black, tiny sigils spiraling along the palm to slowly fill in the scar. If exhaustion didn’t have such a firm hold on him, Izuku would be asking countless questions, but as it were his eyes started to droop, sleep finding him despite the discomfort.
“I own you now, Izuku.” Katsuki hummed into his ear. “And I plan to take full advantage.”
Unconsciousness found him then before he could think of a response more intelligent than fuck.