Two Halves of a Whole - Slugku NSFW

Published on Ao3 here per an agreement with/a commission by Leafcat! Note that this contains some weird/problematic content like monster-fucking and a tail penis? So please heed this warning and feel free to not read it :P

─────

Deku clanked a little as he walked back into the castle, his armoured boots echoing off the room's high ceilings. His steps fell heavy on the hard tile floors, dragging his feet a little now that he was finally home to rest.

He'd had a long morning dealing with idiots who considered themselves adventurers, coming to try – and of course, fail – to slay the Demon King. Whether they were overconfident soloists, or practiced parties of well-coordinated fighter types and their support teams, they still inevitably fell to Deku's power. There was only one man who had ever bested him, a long, long time ago, and he preferred to avoid thinking about that whenever possible.

And so, after his morning of tedious battles, he wanted nothing more than to get home to his castle and the man inside, the man he could finally call his husband again. Pushing open the heavy door had come as such a relief, the tension seeping out of his muscles as soon as he crossed the threshold.

He stopped when he saw Katsuki waiting for him in the foyer, leaning against the railing at the bottom of an ornate staircase. The sight of the pretty face that had come to greet him filled him with light, a smile creeping across his lips when their gazes met. Only a tiny hint of something that seemed out of place in Katsuki's eyes gave him pause, that tiny piece of something giving away his true purpose in waiting for Deku's arrival. Deku stopped to consider it carefully, to decipher what that look might mean, but he seemed to be drawing a blank.

“We knew each other,” Katsuki began, watching Deku's eyes widen. “In what, a previous life? You think I'm a reincarnation or some shit like that?”

Deku tilted his head to one side, considering Katsuki's expression again, a little relieved when he didn't find anger waiting for him in those fiery eyes. Instead he saw confusion, concern, and even a hint of a stubborn little pout. He was familiar with all those expressions, had experienced each of them a multitude of times since they'd reconnected and come together, and he'd learned exactly how to decipher and handle each one. Even before the moment they'd exchanged rings, he knew each and every one of those expressions, let alone in the time since.

“Do you remember?” he asked curiously, leading the way up the stairs to reach their shared bedroom. Thick velvet drapes hung from the windows, blocking out any prying eyes that might come by to sneak a peek, and they cast the room into a comforting shadow. “You didn't seem to remember, before.”

“Does it matter? Tell me the truth, Deku.”

“You are, we did. And I missed you, the whole time we were apart. I was waiting for you, I knew you'd come back to me eventually. Somehow.”

He stepped closer, his eyes strangely soft, a lot like they were on the day they said their vows.

“So we were lovers, back then?” Katsuki asked, voice strangely flat. “In this previous life?”

Deku nodded, taking another step forward to crowd into Katsuki's space, and Katsuki swallowed hard, refusing to break eye contact.

“And that's why you wanted to marry me. In this... life. Form. Whatever.”

“I wanted to marry Kacchan because I love Kacchan,” Deku corrected him, leaning in to nip at the side of Katsuki's neck. “I loved Kacchan then, and I love Kacchan now.”

“Then why didn't you say so before, you dumb Deku? You could have just told me, instead of keeping this shit a secret.”

“But you might not have loved me back.”

“And yet you still took every opportunity to touch me while you were stuck in your stupid slug body.”

Deku shrugged, smiling wryly, and Katsuki's eyes narrowed.

“Kacchan is irresistable,” Deku explained, his tone too sickly sweet for his demon body. “I needed to feel you.”

Everything about his demon body was too sweet, to be honest. His shining eyes, his sweet smile, his fluffy head of hair – and don't even get Katsuki started on the damn freckles. Since when did demons have freckles? But here he was, a pretty little demon in a body that was full of tricks and surprises, who could flip Katsuki onto his back at a moment's notice when he felt like it.

Full of secrets, too, Katsuki was slowly learning.

“Doesn't Kacchan love me too?” Deku licked a stripe up Katsuki's neck, across the little pink spot where his teeth had sunk in only moments ago. “You married me, after all.”

“Maybe I just like your dick,” Katsuki snorted, tilting his head a little to allow the affections. “Maybe I wanted it all to myself, so you wouldn't go fucking any lame extras.”

“It's all yours, Kacchan, there's no one else.” Deku grinned, his tail flicking from side to side as he nuzzled Katsuki's soft skin. “I like yours quite a lot, too.”

“Oh yeah?”

“Yeah,” Deku confirmed, splaying his hand across Katsuki's chest and giving him a little shove. “Let me see it.”

Katsuki couldn't stop the little smirk that twitched at his lips, falling back onto the mattress under Deku's touch. He cast his pants aside and reached for Deku, ready to start removing layers of armour and cloth, but froze when Deku reached between his own thighs. Without a care in the world, he tore his pants apart at the seam, already straddling Katsuki's hips by the time he realised what was happening. His swollen cock hung free from the ragged hole in the fabric, and Katsuki's heart pounded a little quicker.

He wrapped a dark glove around Katsuki's cock, barely needing two strokes to finish bringing it to attention, and then he was lining himself up, dropping down to the base with no hesitation.

“Fuck,” Katsuki hissed, throwing his head back. “Holy shit, Deku.”

“Does that feel good, Kacchan?” Deku teased, raking sharp claws down Katsuki's shirt and shredding it easily. “It feels so good for me.”

“Yeah, fuck, it- it does. Fuck.”

Katsuki wanted to touch, wanted to feel Deku's body, but when he reached out he only found clothing and metal. Not that he could really complain that much, Deku's suit of armour was damn attractive on its own merits. It made the cute demon king look intimidating for once – maybe that was why people were scared of him – and Katsuki couldn't help but eye him over when he put it on, appreciating the way it filled him out and made his slim body look so much bulkier and stronger.

He wasn't a fool, he knew how much strength was hidden inside that lithe form, but seeing him look strong was a whole different story.

“Naughty boy,” Deku tutted, pushing the hands away from his body. “You just lie there and look pretty, Kacchan. Let me handle this part.”

Katsuki growled, gritting his teeth, but Deku only smiled down at him, a hint of menacing sneaking into the expression. He wound his fingers around Katsuki's wrists, coaxing them up above his head, pressing them into the mattress firmly and giving Katsuki a pointed look.

“Has my Kacchan forgotten his place? Forgotten who he belongs to?”

His tail swished back and forth once more, and Katsuki found his eyes drifting, watching it flick as if of its own free will, even though he knew very well that Deku had full control over it. Deku caught the glance, eyes glittering with mischief when the stubborn gaze quickly darted back to his, and Katsuki bit back a moan when Deku's ass stroked at his cock. It slowly dragged up his shaft as Deku rose up on his knees, squeezing tight all the way, and it was all Katsuki could do to stay silent.

“Let me hear you, Kacchan,” Deku instructed, shaking his head. “Don't try to hide your little voice.”

Katsuki's eyebrows lowered, and Deku took a grip on his chin, tilting his head back to look at him properly and exposing his pale neck in the process. He was such a stubborn little thing, Deku mused, but that just made it all the more fun to torment him.

He sank back down, and Katsuki's breath caught. It was so hard to keep quiet, but he refused to give Deku what he wanted.

Yet.

A well-practiced flick of Deku's tail brought a thick leather strap to his hand, and Deku smirked as he wrapped it around Katsuki's neck. He buckled it nice and tight, running the claws of his dark glove along the fabric, rewarding Katsuki with another rough thrust when he didn't fight it.

“There's my good boy,” he hummed, biting at Katsuki's jaw lightly. “My little pet.”

Three quick thrusts in a row had Katsuki throwing his head back, showing off the smooth skin of his neck and the heavy collar Deku loved so much, and the faintest of moans parted Katsuki's lips.

“That's it, Kacchan, let me hear it.”

With his arms stretched above his head, his back arched under tight muscles, and his tattered shirt hanging open over his torso, Katsuki felt oddly exposed. He was at Deku's mercy, feeling that hot ass sliding up and down along his dick, squeezing at him like he thought it might disappear mid-thrust. His breathing sped up in a way Katsuki rarely heard, drawing in and heaving back out in perfect sync with the way he bobbed on Katsuki's dick.

“You feel so good inside me,” Deku praised, tail swishing again, the end opening up a little to let out a dribble of precum. “Open your mouth, Kacchan.”

For all his stubbornness, Katsuki didn't hesitate to obey. He opened his mouth, and Deku's heart fluttered at the sight, watching his Kacchan be so obedient beneath him with his flushed cheeks and his glazed eyes.

Deku's tongue poked out, licking across the end of his own tail, wiping up a trail of precum from the member that protruded. The action sent shocks of sensitivity up his spine, and Deku couldn't help but moan, taking another, slower lick across the dripping slit. Katsuki's eyes darted to it, his own mouth opening a little wider, and it only made Deku even more horny to see it. He upped his pace again, turning his slow, smooth strokes into a rough pounding, up and down on Katsuki's cock to fuck himself hard and fast. His tail flicked again, this time down toward the obedient little husband beneath him, and with a hint of a breathless smile, he stuffed it in Katsuki's mouth.

It felt so warm and wet inside, Katsuki's tongue swiping back and forth over the bulge of Deku's tail penis, and the one between his legs bobbed with his movements. It was hard and swollen, begging for attention, leaking all over Katsuki's abs as it moved with Deku's thrusts.

He tore his glove off and threw it aside, wrapping his hand around the shaft, and Katsuki watched with glazed eyes as Deku fucked himself, jerked himself, and fucked Katsuki's mouth all in sync with each other. Deku was full of stimulation, whining and moaning as he frantically continued his pace, chest heaving as he struggled to get enough air in his lungs.

Katsuki swallowed around Deku's leaking tail, eyes rolling back in bliss, and the vibrations that coursed through his throat were enough to tip Deku over the edge. He pumped Katsuki full of his fluid, smirking when he felt the cock in his ass respond with a burst of its own, filling him up with a warm, slick fluid that felt so good inside of him. He leaked around the shaft as he continued pumping, refusing to let up his pace even though he knew Katsuki had run dry, even his cute little whimpers reduced to silence as he struggled to handle the overstimulation.

Katsuki reached for him, and Deku almost pushed his hand away again, but then he felt the warm hand and thick fingers wrap around his cock, jerking him haphazardly as best as he could manage. Just the sight of Katsuki trying so hard to get him off, even when he was fucked out and exhausted, was enough to push Deku over that final edge. A dam inside him burst, and cum shot straight onto Katsuki's chest and stomach, barely missing the pretty collar. Like an animal marking its territory, he filled with a light, airy joy at the sight of Katsuki covered in his seed, a smile stretching across his lips as he leaned in for a kiss.

“My Kacchan is such a good boy,” he cooed. “I love you so much.”

Katsuki nodded, his arm wrapping limply around the back of Deku's neck to hold him close, and for a minute they just lay there in their own filth, sharing breathless kisses. Deku's hands stroked at spiky hair and warm, thick leather, while Katsuki's fumbled at Deku's hips and back, relishing in their permission to finally touch.

Tired hands found the straps on Deku's armour, fumbling at the buckles and catches to start removing it, and Deku smiled again. He nipped at Katsuki's lower lip, feeling his mouth open wider, and closed his eyes as he let Katsuki begin to strip him.

He expected to hear metal clang against the floor as it fell, but Katsuki held every piece with care, setting it down beside them on the bed – away from the sticky puddles – to clean and hang later. It was such a tiny gesture, but Deku felt his heart swell. If it was physically possible to love his Kacchan more than he already did, he was pretty sure that moment would have done the job.

Katsuki's hands shifted, casting aside the remains of his shirt, and for a moment they parted. Deku smiled again, his hand slowly tracing a path from Katsuki's neck and the heavy collar, down to his belly button stained with two sets of cum, feeling the body shiver beneath him. When he stepped back, though, Katsuki followed. He stumbled to his feet, blushing when Deku grabbed him to steady him, and together they limped their way to a waiting bathroom.

The tub was huge, set in the floor with walls of shining stone, complete with a little staircase to get in and out. Izuku set it to work pumping hot water for them to soak in, then pulled up a bucket. He reached to start scrubbing Katsuki down, but Katsuki beat him to the punch – gentle hands lathered him up, and Deku smiled once again, savouring the care in his touch for a minute before reaching to return the favour.

Deku unfastened the heavy collar as he cleaned, planting a little kiss on the sweaty skin it once covered, and Katsuki tilted his head a little to make room. He trailed little nips down the side of his neck, then replaced them with his hand, rubbing circles along tight muscles. Katsuki hummed his appreciation at the soothing strokes, smiling softly as he let himself just relax and accept it for once, without arguing about who was more exhausted or who made the most mess. It felt good to just enjoy each other's company, to take in their shared comfort and mutual appreciation for the other – maybe Katsuki would allow it more often.

Clean and bare, they climbed down into the tub together, and Deku dropped himself heavily into Katsuki's lap. Katsuki grumbled a protest, more for show than anything else, but wrapped his arms around Deku's waist all the same. He ran his hand up Deku's torso, spreading warm water over his skin as he caressed every muscle, and Deku leaned back to press their skin together closer.

“You're so good,” Katsuki admitted, kissing Deku's jaw. “Holy shit, Deku.”

“You think so?”

“You know you are, asshole,” Katsuki snorted, watching Deku's cheek twitch as he tried to hide his smile. “I've never cum so much in my damn life.”

“Mm... No, you always cum a lot. Always did.”

“Only with you.”

“Good. I only want it to be with me.”

Katsuki raised his hips a little, twitching against Deku's bare ass in his lap, and Deku's smile stretched into a wicked grin when he felt the hardness beneath him.

“Already, Kacchan?” he teased. “I must be good.”

“Damn right,” Katsuki trailed kisses down across Deku's shoulder, hands sliding up to hold his pecs. “Maybe I should make a mess of your pretty bathtub.”

“Our,” Deku corrected, grinding down against Katsuki's waiting cock. “Make a mess of our bathtub.”

“If it's your bathtub, I won't have to clean it.”

“I'll make someone else do it.”

“You'll pay someone?”

“That works too.”

Katsuki sighed, but the morality debate was quickly halted by his dick twitching again, determined to find its way back into Deku's ass. Deku smirked at him, and Katsuki caved, wrapping his hands around Deku's strong thighs and hitching him up.

Deku was surprised when Katsuki flipped them over, bending him over the edge of the bath, but when the strong hand ran along his ass cheek he decided against protesting. He didn't mind if Katsuki was in charge once in a while – they all knew who actually wore the pants in their relationship, he didn't need to constantly prove it.

Katsuki spread the slim legs to give himself room to slot in between, watching the long, thick tail move aside without hesitation. His hole was pink from his brutal thrusts as he rode the life out of Katsuki's dick, but it twitched as if it could be excited to feel Katsuki so close, and Katsuki found himself grumbling as he hooked a finger inside.

“Mmm, Kacchan, still stretched from before,” Deku pointed out. “Fuck me, okay?”

“Didn't bring the lube with me,” Katsuki huffed.

“It's fine, I don't mind.”

Katsuki was wary, but he didn't bother to question it – for one thing, he was fucking desperate to get back inside of him, and for another, Deku wouldn't change his answer no matter how times he asked.

Katsuki had learned that the hard way.

Giving in to his pathetic desperation, he lined up his dripping cock with Deku's hole, making a slow little test thrust to see how his lover would react. Somehow, though, Deku always managed to surprise him – this time, it was the long tail that caught him off-guard, winding around Katsuki's back and pulling him in demandingly. Katsuki hissed as he felt himself sink in, but Deku just moaned long and low, his ass tightening around Katsuki's shaft like it might be the last time he ever felt it.

Katsuki liked to think he was a strong man, but when it came to his Deku, he was so, so weak.

Pressing his hand into Deku's back, he pulled his hips back, sliding out of his tight warmth despite the way it seemed to fight to keep him there. Deku turned his head to the side, peeking back at what he could glimpse of his Katsuki, but just as he opened his mouth to demand more, Katsuki's hips snapped.

Skin hit skin with a loud slap, Deku's stomach pressed hard into the edge of the bath, and Katsuki's cock filled him up so perfectly, hitting his prostate like it was the sole reason his dick had even been created. They were made for each other, carved from the same flesh, two halves of a whole that should never have been separated – and never would be again, if he could help it. Deku tried his best to voice all those thoughts, to articulate the love and adoration that filled his mind and soul, but another quick thrust had him babbling nonsense instead as he forgot how to work his tongue.

“I love you,” he spluttered out, as Katsuki fucked him so perfectly, so rough and yet somehow so tender. “Kacchan.”

“Love you too,” Katsuki snorted, breathless as he tried to keep his brutal pace even with the friction that started to form between them. “Cum for me, Deku.”

He reached a hand around Deku's hip, fumbling for his throbbing cock, stroking him in time with the slightly more erratic thrusts. As one, linked together into their rightful whole, they spilled what remained of their semen – Deku's staining shiny stones with a cloudy coating, Katsuki's painting Deku's insides and claiming him once again as his own.

For a minute, neither of them spoke; still locked together as they dripped sticky fluids into the water, but then a smile crept across Deku's slack features.

“Idiot,” Katsuki said softly, finally detaching himself from the mess and leaving Deku cold despite the hot water surrounding them. “Feel so fucking good for me.”

“Hug me, Kacchan.”

Katsuki wanted to complain about the demand, wanted to sarcastically ask what happened to please, but his arms were already dragging Deku into his lap before he could even form a sentence. He sat Deku sideways across his lap, where they could snuggle into each other happily, and Deku did exactly that – a fearsome demon of horns and armour and sharp claws, reduced to a man who nuzzled Katsuki's hair like some kind of weird, over-sized kitten.

“I had a long morning,” Deku yawned, closing his eyes and rubbing his cheek against damp, blond spikes. “A lot of idiots to deal with.”

“Yeah?” Katsuki hummed.

“Made me so happy to come home to you. To this.”

“You're really fuckin' sappy for a Demon King,” Katsuki teased. “Yeah, you're a good fuck, I'm glad you came home too.”

“Home,” Deku repeated without thinking, catching Katsuki burning red when he cracked an eye open to peek, and quickly cutting off the retraction he knew was coming. “Don't take it back. It is. It's our home, you and me. Husbands.”

“Shut up,” Katsuki grumbled, stroking his back fondly all the same. “Welcome home, Deku.”

“It's good to be home.”