The Perfect Demon (Demon Slayer)

A/N: 1st Poll Winner. I actually had a lot of fun writing this.

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'What extraordinary vitality.'

She could tell a lot about a human just by looking at them, by sensing them. And when she first saw this boy... she had nearly eaten him outright. He felt so alive, so incredibly potent with energy, with lifeforce. She despised this primal part of herself, but at the same time, she knew that she would enjoy feasting on his flesh.

But no. No, Kenji Sato would be far more useful as a demon.

After giving him a few drops of blood, however, she instantly regretted it.

Yes, he was overflowing with lifeforce, but he had nothing else. No talents, no skills. Kenji was incredibly stubborn, and that was it. He hadn't been able to escape the slums even with his vitality, so she hadn't thought much of his intelligence... but you'd think that he'd have at least ONE redeeming quality!

The only thing he had going for him was that he was presentable. Brown hair and eyes were fairly boring, sure, but Kenji was handsome enough to meet her standards.

The rest of him, though, had left a lot to be desired.

But. But after she graces him with her blood. He dares. He dares...

"I can't go into the sun anymore? That fucking blows."

<At least she's got nice tits.>

Muzan nearly killed him then and there. But she had relented, because Kenji was new. He was not used to her rule. To her regime.

But then Kenji went and did the unthinkable.

The very next day, he went into the sun.

Muzan had sensed it– at first, one of her demons were burning. That wasn't anything new, since her underlings tended to be stupid at times, but then she singled in on the connection. It was Kenji. Muzan delved into his mind, wanting to know why Kenji would kill himself, and she felt her face crinkle in disgust.

Kenji just wanted to see the sun. He was so stupid. Muzan had just about screamed through her control, determined to make his ears bleed, but... but then she felt it.

Kenji started dying... slower.

He had overwhelming vitality, she knew that. That vitality only increased further after she made him hers, granting him regeneration stronger than some of her Upper Moons. But to think that Kenji's Demon Art would be this. The power to slowly build up resistance to anything that could hurt him, to anything that could kill him.

Adaptation.

Kenji was adapting to the sun.

Muzan trembled, her hands shaking. After one thousand years of searching, hunting, and scavenging, a solution had decided to fall right into her lap.

For the first time in eternity, a demon, her demon, would stand in the sun.

<Miss Demon didn't know her shit, huh,> Kenji thought idly, still burning slightly.

Muzan's jaw clenched, but she smiled. Kenji didn't know it, but he had just granted her a boon larger than any of her demons before him. Even if Kenji was... Kenji, Muzan had vowed to reward anyone that gifted her the one thing she so desperately craved. So she was inclined to grant Kenji a single, unconditional favor. Just one.

It was only fair.

***

'A favor, huh?' Kenji thought.

It was a little odd, but he could wrap his head around it. Miss Demon was like, the Queen of all Demons, and demons couldn't go into the sun... until he did it. He asked if that meant every other demon was just trash, but no. Clearly frustrated, Miss Demon (who still wouldn't tell him her name for some reason) explained what a Demon Art was.

And his was Adaptation, which was self-explanatory.

He also realized just how close he was to actually dying, but he lived, so whatever.

And since Miss Demon had control over other demons, including him, she could use her ability to grant herself the same resistance to sunlight.

Or as she had put it, "to see the sun for the first time in 1000 years..."

Kenji knew she was old, but goddamn.

'But still, a favor...'

Kenji stared ahead at Muzan, biting his lip. She was super cute, with frizzy black hair, piercing red eyes, and nice and perky tits– that last bit only made sense, given how she'd never age, physically at least. She was really fucking old. And then there was her ass, and Kenji enjoyed the sight of her kimono straining around her vulgar lower half.

He wanted to fuck her so bad.

Not to mention the fact that, well... he was a demon. Even if his newfound strength would let him have pretty much whatever he wanted, including whatever woman he wanted, Kenji was going to live forever. If he tried to settle down with a human woman, he would either have to slowly watch her shrivel up and die, or ask Miss Demon to turn her too. That sounded like it would be a hassle...

And he already had this perfect, hot, fuckable, demoness right in front of him.

Kenji could see it. Living in a nice, big manor out in the woods, knocking up little Miss Demon again and again as she spends the next 1000 years taking his cock, pumping out his kids. Turning the Queen of Demons into his ever-loving, ever-fertile housewife. Spending every single day dumping load after load of spunk into her ever-tight, ever-wanting pussy...

But he couldn't just ask her that.

It'd be pretty crass of him.

"Er, I guess I could use a nicer house?" he suggested.

Miss Demon had been looking at him kind of weird the last few minutes, her face showing a number of emotions... but he understood that look. She was annoyed.

Very, very annoyed.

"You belong to me, you know that, right?" she asked, her voice quiet, but firm.

"Well, yeah."

He already knew that.

"You're mind, body, and soul are mine," she drawled, and since Miss Demon had already told him that, he just nodded. Then she growled. "That includes your thoughts."

Kenji blinked.

"Oh."

A lot of things rushed into his mind at once. Miss Demon knew everything that he had thought the last few days, including how much that he had objectified her. Including how much he wanted to bend her over a table. But... even though she could kill him in an instant, whenever she wanted to, she hadn't.

Kenji reached out and grabbed Miss Demon's ass, giving it a firm squeeze.

He watched her shudder, her jaw clench. She was angry. Furious. But... instead of blowing up his heart, she just stood there. Staring at him with a silent rage.

Kenji grinned. He was really going to fuck–

"You get one night," she growled. "Nothing more– mmMMMPH?!"

His hand still firmly gripping her ass, Kenji pulled her in close, wrapping his arm around her back and going in for a kiss. He forced his tongue into her lips, sucking her face as he licked at her teeth and gums. Furiously making out with his Queen, Kenji's hands explored her body, sliding down her figure as he caressed her.

Her breasts pressing against his chest as he both of his hands sunk into her ass, as he held her flush against his body.

Then he gripped the fabric of her kimono and pulled. Tearing it to pieces. Revealing her perfect pale ass to all that dared to look.

She growled into his mouth, furious, but she didn't act on that anger.

Unfazed, Kenji lifted Miss Demon up by her butt, his hands sinking even further into her ass as he held her in the air. Carrying his Queen through the halls, he continued to suck on her mouth, now focusing on her fangs. They were incredibly sharp– he's already nicked himself a couple times, but that just caused his Queen to suck back even harder... since blood tasted good now, for some reason. But they were also sensitive, and he quite enjoyed the way that she twitched and shuddered under his attack.

Miss Demon had yet to moan or gasp, but he was nothing if not determined. Even if she was the Queen of Demons, he was going to make her lose to pleasure.

<Muzan,> he heard Miss Demon's voice in his mind. <Call me Muzan. W-Worm.>

Kenji chuckled into her mouth, just a little bit. For all that Muzan was unrelenting evil, she could be incredibly cute. But before he could set his prize down on his mattress, his vision spun as Muzan threw hurled him against the floor. Putting him flat on his back with Muzan's busty, pale figure towering over him.

She smiled thinly.

"Now, I'm going to fuck you– HHNNNG!!"

Kenji grabbed Muzan by her hips, and forced her down on to his cock hard. He felt Muzan's hymen snap, but he didn't let that stop him for a second. This was the Queen of Demons that he was fucking. Determined to win, Kenji immediately started thrusting up into her tight cunt as hard and fast as he could.

"MMMM!! You– HHNNNNNG!!"

He reveled in the way she twitched and spasmed, gritting her teeth even as her face flushed with arousal, even as drool leaked from her mouth. Still fucking her warm, tight pussy, Kenji flipped the two of them over, putting her back on the floor. Never stopping his assault, continuing to thrust his cock into her sopping wet cunt.

Kenji hadn't slept with anyone before this, but he knew. They'd never compare. Not only was Muzan's pussy tight, but he could feel his girth forcefully stretching her folds... only for her cunt to clamp right back down, regaining its overwhelming tightness. Doing everything it could to drain the life out of his cock. This was the pussy of a regenerator, a pussy that would always be far too tight for him. It was awesome.

It was only a little over a minute before he cummed, spurting out load after load of his hot, virile spunk into her womb. Firmly hilting his cock in her snatch, holding her hips as he kept his throbbing cock pressed up against her womb. He watched Muzan's eyes go wide, as if this was a surprise of some sort. She should've known that he was going to do this from the start.

Then after filling her up for a solid minute... he immediately started fucking his Queen again, his refractory period non-existent.

Kenji was no longer human, but demon.

Not to mention that he was nowhere near satisfied.

Still fucking his Queen hard and fast, he slid his hands up her figure, reaching for her fat, perky tits. Kenji clenched down on them, hard. Muzan let out a grunt, biting her lip as her eyes narrowed, staring up at him. Angry and aroused. She growled, but Kenji just started slamming his hips into hers harder, grinning as she watched Muzan twitch under him.

The noise of skin harshly slapping skin filling the room.

PLAP! PLAP! PLAP!

Still fucking her nice and rough, and still mauling her tits with his hands, Kenji leaned down and pulled her into another kiss, pushing his tongue past her lips and attacking. To his surprise, Muzan made out with him with equal fervor. Kenji felt her tongue running along his, stretching out and coiling around his, like that of a snake. He also felt Muzan's hands sink into his hair, desperately trying to pull him further and further into her mouth.

He retaliated by squeezing her tits ever harder, earning him another growl, followed by a groan as he plowing her pussy even rougher than before.

Kenji continued to fuck her for quite a while. Filling her up with his spunk over and over, a small puddle of semen forming underneath her cum-stuffed pussy.

Uncaring for their surroundings, only wanting to knock up the demoness beneath him.

"S-Sun..."

His thrusts slowing just a bit, Kenji watched as sunlight glared through the window, glistening on her ever pale skin. He watched as Muzan's face burned up just a little, and how just a few seconds later, her regeneration won out. Two single tears streaming down the sides of her face. And then she smiled, and Kenji might've only known her a few days...

But the Queen of Demons probably hadn't smiled like that in a long, long time.

She was pretty bad at it.

"Ugh, you ruin everything," she huffed, annoyed. But Kenji wasn't going to change the way he thought just to appear nice. That sounded like a hassle. Looking down at her mildly annoyed expression, he pressed the tip of his cock against her womb, cumming one last time. His spunk splashing out around his mast as her pussy was filled to the brim and more.

Then he pulled out, hold his cock above her as he let out a few shots across her hips, breasts and stomach, earning him yet another growl.

He wanted more, but it looks like the night was over...

And that was all Muzan had promised him. Even if teasing her was kind of fun, he didn't want to push her too far. Since they'd be alive forever, he had time. Kenji wouldn't want to hurt his chances of having her forever. No, after last night, Kenji was determined to slowly but surely swoon her, to break down all her walls and make her his wife.

Sooner or later, she was going to be his.

Then Kenji's eyes went wide as multiple tentacles shot out of her, curling around his figure as they held him in the air. Muzan always looked a little crazy, but Kenji could now feel her craziness bleeding over through her control, along with her overwhelming anger. He wondered for a moment if she was about to kill him... but no.

"I'm going to be yours?" she hissed, her face crinkling with disgust. "No. I am not yours, and I will never be yours. You are MINE. You belong to ME."

Then he watched as a bunch of little mouths open all across her body. Long, slimy tongues slipping out of them, cleaning her figure of sweat and spunk. Then he watched as a single tongue left her snatch, licking her pussy lips clean, slurping his cum deep into her cunt while letting out a soft 'ahhh.'

Immobilized by her tentacles, he felt one curl around his cock, guiding him back to her freshly cleaned pussy.

"And I did not say you could stop." she growled. "I am going to drain you dry and more. You are going to fuck me until I am satisfied, be it days, months, or years. You will be fucking me until the day you die. Nothing that you say or do will change that. You are MINE, and I will use you as I see fit."

Kenji let out a groan as she took his cock to the hilt, her pussy somehow even tighter.

Muzan gave him a wicked smile.

"So you better get used to this, Kenji."

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