A demons warmth
Summary: Muzan never thought he’d see the day we’re one of his demons remained warm.
Warnings: 18+, fem!reader, smut, porn with plot, fingering, oral, dirty talk, unprotected sex.
Don't mind any errors, I didn't fully edit this. Also, I was half asleep.
You were out late one night, your parents had told you to be in before sunset. You obviously didn’t listen, the sunny day quickly turned into cold night.
The breeze making you shiver. Your kimono was cheap and thin, leaving little to no room for warmth. Your parents aren’t rich but they try to give you what you what ever you ask for.
The sound of your shoes hitting the ground soothes you from the quiet watching night. You speed up your trek home, the quiet making you uneasy.
The sounds of the alarms distant in the background, they were there to tell people it’s getting too late, that they need to head back home.
You can see your home in sight, just over the bridge and you’re practically there.
A branch breaking catches your attention, you still, despite all your instincts telling you to run.
But you knew exactly what it was, a demon.
They had been roaming this side of town more often, exactly what the alarms were installed for.
Your head snaps to the woods, feeling eyes watching you.
A silhouette appears coming out the woods, then three more disperse from behind it.
Your brain finally catches up and you take off running. Your lungs burn almost instantly. The forest swallows you whole the moment you break into a sprint.
Branches claw at your sleeves as you push them away from your face, the bridge now so close it feels like salvation if you just—
A blur drops in front of you, your body tries to stop before you even think to. You lose your footing, falling on your knees.
The figure straightens slowly, as if it had all the time in the world. Pale. Wrong. Its presence presses against your chest like a hand squeezing your ribs from the inside.
Behind it, the other three demons step out of the dark like they’ve been waiting for you to arrive.
You turn to crawl away, a hand grabs your ankle. Without looking back you thrash your legs, trying to kick at whatever and whoever you could.
Another hand grabs your other leg, pinning them to the ground.
The demon flips you onto your back. You get a look at the demon, his eyes captivated you the moment you see them, three eyes decorating each side of his face. His long hair pulling into a ponytail.
You don’t get to be in awe long when the world tilts. Then the forest goes quiet in a way that feels… intentional.
A heavier presence arrives. Not rushing. Not hunting. Approaching.
The demons shift immediately subtle, fearful, obedient. Even they seem smaller now, like prey pretending not to breathe.
And then you see him.
He steps through the trees like they belong to him. No sound. No warning. Just presence.
He looks at you like you are already something decided. Not an accident. Not a surprise. A result.
“You’re late”
Two words. That’s all he spoke, and it still managed to scare you. Him being a demon didn’t scare you, it was the fact that the other three seemed to be terrified of him.
Your fingers dig into the ground as you try to crawl back, the grip from the first demon tightens on your ankles.
His gaze drops to your neck. Then your pulse. Then your fear.
“You were seen.”
The demons lower their heads further.
Your throat tightens. “Please! I didn’t— I didn’t do anything—” you stutter over your words.
He paused, the quiet of the night filling your ears. Your eyes stay on him, watching his every move. He lets the moment hang in the air, and your eyes finally connect.
His face is calm as he steps towards you, one moment he's several steps away. Next he's crouched down infront of you, close enough that you can feel the air shift around him.
It was cold and suffocating, like everything around him was holding its breath.
His hand lifts, and your instincts tell you to scream, to run to do something. But you can't, your body feels like it's glued to the ground.
He doesn't grab you, though, no, his hand gently lands onto your face, petting it like you would a stray cat.
You feel his sharp nail graze across your cheek, your body involuntarily shivering. He lifts your chin, forcing you to look at him.
His hand slides down to your cheek, and he gently presses the pad of his finger against your neck. You can feel your pulse beating against his finger; the hold is firm, but not enough to hurt.
He drags his fingers across your neck, reaching slowly until they stop at your pulse.
The pad of his finger presses harder into your neck.
You can feel your own pulse thumping against his finger; his hand stops, and presses deeper into your skin. His nail digs into the soft skin, causing a speck of blood to form.
You flinch from the pain, your heart feels like it'll jump right out of your chest, and you know he can tell. You look up at him, and his face is eerily calm.
"You've seen too much," his voice was monotoned, like he'd said that exact sentence one hundred times.
"I won't say anything! Please!" You cry out.
It's almost like he can't won't hear your pleas. You start thinking about the way your mother told you to be inside before dark, how you shouldve listened to her.
His eyes glow in the night, a deep ruby red that catches you off guard. For a moment, your mind quiets, your racing heart slowing under his gaze.
Then his hand lifts. Long fingers, nails sharp enough to tear through flesh with ease.
One finger comes to rest beneath your chin, tilting your head back. Gently, he parts your lips.
His other hand lowers, slow and deliberate.
Two drops of blood fall into your mouth, small enough to be seen, but not enough to be felt. He lets go just as smoothly, watching you.
A faint, satisfied curve settles on his lips.
“What have you done to me?!?” Your voice is hoarse as you speak.
The smirk dissipates from his face, replaced by a nonchalant expression.
“Ive changed you”
His palm comes to your face, and he pats it like you would pet a cat.
Then his body stills.
His fingers rest on your face, like he’s trying to feel for something wrong or incomplete. His eyes are now focused on your cheek, where his hand rests.
You watch his brows furrow like he’s thinking about something.
“You’re warm”
He’s not talking to you, more to himself. He’s watching his hand like it offended him in some way.
“Kokoshibo, feel her skin” the 6 eyed demon walks forward, gently placing a hand on your other cheek. Each of his eyes widen in shock? Surprise? You can’t tell.
“That shouldn’t be possible,” he mumbles in disbelief.
Their hands are cold on your cheek, you look up at them, trying to force your eyes to stay open.
What ever he did to you drained most of your energy. You see the leader motion one of the others over. “Akaza, carry her” he demands "She stays alive"
You black out as he reaches you.
Your eyes shoot open.
White.
That’s the first thing you notice, white walls, bare and unfamiliar. No windows. No light. Just a quiet that feels… different.
A groan slips past your lips as you push yourself up, your back protesting immediately, screaming at you to lie back down.
You pause, breath uneven, and bring a hand to your face, rubbing at your eyes.
The exhaustion is still there.
Heavy.
But… not right.
You slowly get out of the bed. The door is unlocked when you turn the knob. You immediately think it’s a trap, carefully you exit the room.
The hall was long and narrow, you tip toe down the hall, looking around each corner to see if anyone is there.
“Aren’t you supposed to be in bed?”
You almost jump out of your skin, turning to the voice you quickly recognize him. It was one of the three demons there.
“Why am I here?” You question.
He smiles his colorful eyes shining as he does. “Muzan has an interest in you and I want to know why”
He steps closer and you step back, bracing yourself for anything. “Leave her alone, dumbass”
You turn around, and the other one is there. You remember hearing his name, but you can’t recall what it is.
The two demons start to argue, but it looks more like the white-haired one is enjoying the argument.
You look around while they're distracted, trying to find a way out. You see two doors; one of them is cracked open, so you assume the demon with the tattoos came out of it.
The other is shut. You slowly step back as they argue.
You creep back until your back hits the door. You find the knob; your eyes are still focusing on the two arguing.
You managed to open the door without them noticing, slipping into the room it’s dark.
You try feeling around for a switch or something, finally after what feels like forever you find one. Flipping the switch brights up the whole room.
You looks around, everything looks normal, like a regular room.
“Youre awake sooner than I expected”
The voice startles you, your head whips around and you see him. Sitting in the chair across the room, his legs crossed over each other and his hands in his lap.
“What do you want from me?” The question came out shaky.
He doesn't say anything at first he just stares at you. Then with one hand he ushers you closer, his pointer finger curling and uncurling.
You hesitate, too afraid of going closer.
“I’m a very patient man, but I’m only going to ask you once”
His voice was low, like he didn't want anyone to hear.
You moved closer for your safety, keeping your arms at your side and your head lowered.
He uncrosses his legs, his elbows resting in his thighs.
When you're close enough he grabs you pulling you into his lap. The speed of his movements surprised you, a gasp left your mouth before you could fully comprehend what happened.
“Youre different” he states. He says it like he isn't talking to you, more like he's confirming something he already knew.
His hands run slowly up and down your arms, like he's trying to embed the feeling into his mind.
“What do you mean?” You're voice is steady as you speak.
“…Youre warm” he starts. “Its unnatural”
Now that you think about it… He's right. His hands against your skin is cold, like he stuck his hands in ice.
The demon from earlier… Akaza, you felt it when he picked you up after you'd passed out.
You hadn't felt the coolness of them until then.
He doesn’t answer your question.
Instead, his gaze lingers a moment longer than necessary, measuring, calculating.
“…Interesting,” he murmurs at last.
Not approval. Not concern. A conclusion.
His hand withdraws from your skin, slow and deliberate, like you are no longer something requiring immediate examination.
“You’ll stay here,” he says simply, already turning away. “Until I decide otherwise.”
There is no invitation for argument.
No space for refusal.
And just like that, the air shifts, his presence reasserting control over the room, as if the conversation itself has been sealed.
You feel it then. Not danger.
Finality.
Your body grows heavier, exhaustion creeping back in like it was only waiting for permission.
The edges of the room begin to blur.
And the last thing you understand before everything slips away.
Is that you were never leaving.
Two years passed without you ever leaving his side.
He still looked at you like an experiment, something unresolved, something he hadn’t quite finished understanding.
But life in the estate had shifted, in small ways.
You’d changed things.
As one of the few women there, you’d slowly added touches of yourself to the space, softening what you could. Your room was the clearest example of that: decorated in the colors you’d always wanted back home, warm and familiar in a place that was neither.
Even the others had adjusted around you in their own ways.
You’d somehow managed to become… friends with Akaza. Or something close to it. He’d never admit it, of course, and he still acted like your presence was more tolerable than welcome, but he stayed anyway.
And Muzan… Muzan still watched.
Still analyzed.
Still waiting for something in you to finally make sense.
Kokoshibo usually stayed in his room, away from your “nonsense” as he’d call it. You never minded though, you only ever bothered him when you needed something from him.
And Douma… well, he rarely left your side. He always seemed curious about you, your habits, your traditions, the foods you preferred, like you were something fascinating he couldn’t quite categorize.
You never complained. In a strange way, you didn’t mind his company.
Even after two years, you still couldn’t fully fall asleep.
Life here was… comfortable, in its own strange way. You were taken care of, watched over more often than not.
And yet.
It was hard to forget that just two years ago, you had been human.
You laid back on the bed, your arms splayed out. The ceiling looked interesting tonight, it seems to be the only thing you find comforting.
The room was quiet in a way that felt too controlled to ever be called peaceful.
No wind slipping through cracks. No distant night sounds from outside. Just silence that had been carefully maintained, like even the world beyond your walls had been told to behave.
You exhaled slowly.
Even after two years, your body still didn’t fully understand rest here. Sleep came in fragments, light, restless, never deep enough to feel like escape.
Sometimes you wondered if it was you.
Or if it was the place.
A soft knock broke through the quiet.
Your gaze shifted toward the door, though you already knew before it opened who it would be.
The handle turned.
And the air in the room changed before he even stepped inside.
Muzan entered like he belonged everywhere and nowhere at once, calm, composed, as if your thoughts had simply paused to make space for him.
His eyes found you immediately.
“You’re still awake,” he said.
Not a question.
A fact he had already accounted for.
And suddenly, the ceiling didn’t feel quite as interesting anymore.
You nod.
He stood in the doorway, watching you, looking for any signs that you’re uncomfortable. Something he started doing last year when you hid how uncomfortable your kimono was.
Slowly, he entered fully, closing the door behind him.
He looked at you like he was unsure of your nod, when you looked at him his eyes look different, like they were searching for his next meal. You sit up on your elbows.
"Sit up," he said quietly.
You did, pushing yourself upright as he approached the bed. The mattress dipped slightly when he sat beside you, close enough that you could feel the cold radiating from him, a stark contrast to the warmth of your own skin.
His hand reached out, fingers brushing along your jawline with clinical precision.
"Soft," he murmured, more to himself than to you. His thumb traced the curve of your cheek, then down to your throat where your pulse jumped beneath his touch. "Always warm. Even now."
His other hand moved to your shoulder, sliding the fabric of your kimono down slowly, deliberately, exposing your collarbone. His eyes followed the movement with that same analytical focus he always had, like you were a puzzle he hadn't quite solved.
"Tell me something," he said, his voice low and measured. "When you were a child, did you ever feel cold?"
The question caught you off guard. Your breath hitched as his fingers traced lower, skimming over your chest, circling one nipple through the thin fabric still covering you.
"I—what?"
"Answer me." His tone didn't change, but his hand stilled, waiting.
"Sometimes," you managed. "In winter. When—"
His fingers pinched lightly, and you gasped.
"Be specific." He pulled the fabric aside completely now, baring your breast to the cool air. His thumb brushed over your nipple, watching it harden under his touch. "What did the cold feel like?"
Your mind struggled to focus as his hand continued its exploration, sliding down your stomach, pushing the kimono open further.
"Like... like my fingers would go numb," you whispered. "My nose would hurt. I'd—ah—"
His hand had reached between your legs, cupping you through the last layer of fabric. He pressed firmly, his palm grinding against you with deliberate pressure.
"And now?" he asked, his eyes lifting to meet yours. "Do you feel cold now?"
"No," you breathed.
"No," he echoed, almost thoughtful. His fingers hooked into the fabric and pulled it aside, exposing you completely. "You never do."
The first touch of his fingers against your pussy made you jolt. He was cold, so cold it almost burned, but he didn't pull away. Instead, he explored slowly, methodically, his fingers sliding through your folds with clinical curiosity.
"You're wet," he observed, his tone unchanged, as if he were noting the weather. One finger circled your entrance, gathering the slickness there. "Your body responds like a human's would."
He pushed one finger inside you, and you couldn't stop the small sound that escaped your throat.
"But you're not human anymore," he continued, adding a second finger, stretching you. His thumb found your clit, pressing in slow circles. "So why do you still feel like this?"
You couldn't answer. Your hips moved against his hand involuntarily, seeking more friction, more pressure. He allowed it, watching your face with that same intense focus.
"Did anyone touch you like this before?" he asked suddenly. "When you were still human?"
Your eyes flew open. "Muzan—"
"Answer me." His fingers curled inside you, finding that spot that made your back arch. "Did they?"
"No," you gasped. "No one—"
"Good." The word was soft, but there was something possessive in it, something that made heat coil tighter in your belly. His fingers moved faster now, pumping in and out of you with purpose. "Then I'm the only one who knows how warm you are inside."
The pressure built rapidly, your thighs trembling as his thumb worked your clit in tight circles. You were close, so close.
He pulled his hand away.
You made a sound of protest, but he was already moving, positioning himself between your legs. His hands gripped your thighs, spreading them wider, and then his mouth was on you.
The cold of his tongue against your pussy made you cry out. He licked a long stripe from your entrance to your clit, then focused there, circling and sucking with the same methodical precision he'd used with his fingers.
"Muzan" Your hands found his hair, unsure whether to pull him closer or push him away.
He pulled back just enough to speak. "Tell me about your family."
"What?" Your voice was breathless, confused.
"Your parents." His tongue flicked against your clit. "Did they know you were different?"
"I don't—I don't understand—"
"Think." He pushed two fingers back inside you, his mouth returning to your clit. The dual sensation made coherent thought nearly impossible. "Your appearance barely changed when I gave you my blood. You still look human. Still act human." His fingers curled, and you gasped. "Why?"
You tried to focus, tried to remember through the haze of pleasure. "My mother... she said I never got sick. Not after—ah—"
"After what?" His fingers stilled inside you, waiting.
"After I was little," you managed, your voice shaky. "A baby. She told me I used to eat plants before she could stop me, flowers, grass, leaves, even dirt sometimes, all of it.”
His fingers resumed their movement, but slower now, more deliberate. "And then?"
"Then I never got sick again. My mother thought it was a blessing. That I was always warm to hold, always—oh god—"
"Interesting." He sucked hard on your clit, and your hips bucked against his face. His fingers pumped faster, curling with each thrust. "And your father? Did he notice?"
"He—he said I was like a little furnace—even in winter—"
"But you still cried like a human child, didn't you?" His voice was clinical even as his tongue worked against you. "Still laughed. Still felt fear and joy and all those fragile human emotions."
"Yes," you whimpered. "I was—I am—"
"You are an anomaly." His free hand gripped your thigh harder. "You sleep in fragments like a human. You personalize your space with colors and decorations. You form attachments." His fingers twisted inside you. "You react to pleasure exactly as a human would. So tell me, what was in that flower you ate?"
"I don't know—Muzan, please—"
"Please what?" He lifted his head, his chin glistening with your wetness. His eyes met yours, dark and calculating. "Tell me what you want."
"I need—" You couldn't finish the sentence, couldn't put words to the desperate ache building inside you.
"You need to cum?" His fingers slowed to an agonizing pace. "Say it."
"Yes," you whimpered. "Please, I need to cum."
"Then cum." His mouth returned to your clit, his fingers curling hard against that spot inside you, and the tension finally snapped.
Your orgasm crashed through you in waves, your pussy clenching around his fingers as pleasure whited out your vision. He didn't stop, working you through it until you were shaking, oversensitive, trying to close your legs against the intensity.
Only then did he pull away, sitting back on his heels. You watched through half-lidded eyes as he brought his fingers to his mouth, tasting you with that same analytical expression.
"Still warm," he murmured. "Even here."
He stood, and you heard the rustle of fabric as he undressed. When he returned to the bed, he was naked, his dick hard and already leaking at the tip. He was as pale everywhere as you'd expected, his body lean and defined.
He positioned himself between your legs again, the head of his dick pressing against your entrance.
"Look at me," he commanded.
You did, meeting his eyes as he pushed inside you in one slow, deliberate thrust. The stretch was intense, almost too much, but your body accepted him, still slick and open from your orgasm.
He bottomed out with a soft exhale, his hands gripping your hips hard enough to bruise.
"You're so fucking warm," he said, and there was something almost like wonder in his voice. "Like being inside a fire."
He pulled out slowly, then thrust back in harder. You gasped, your hands clutching at his shoulders. His skin was cold under your palms, such a stark contrast to the heat building between your legs.
"Did you ever imagine this?" he asked, his hips setting a steady rhythm. "When you were human, did you think about being fucked by a demon?"
"No," you managed. "I didn't—I didn't know—"
"You didn't know demons existed." He thrust harder, deeper. "You didn't know I existed. And now you're here, taking my dick like you were made for it."
His words sent a fresh wave of heat through you. Your legs wrapped around his waist, pulling him deeper, and he made a low sound of approval.
"That's it," he murmured. "Show me how much you want this."
His pace increased, each thrust driving you higher up the bed. One of his hands moved between your bodies, his thumb finding your clit again. The added stimulation made you moan, your pussy clenching around him.
"Tell me," he said, his voice strained now. "When did you stop being afraid of me?"
The question cut through the haze of pleasure. You looked up at him, at the intensity in his eyes, and realized he genuinely wanted to know.
"I don't know if I ever stopped," you admitted breathlessly.
Something flickered across his face, satisfaction, maybe, or something darker.
"Good," he said. "You shouldn't."
He fucked you harder then, his control slipping just slightly. His thumb worked your clit in tight circles, and you felt yourself climbing toward another orgasm, faster this time.
"You're going to cum on my dick," he told you, his voice low and commanding. "I want to feel how tight your pussy gets when you come."
"Muzan—"
"Now."
The command pushed you over the edge. Your second orgasm hit even harder than the first, your whole body tensing as pleasure rolled through you in waves. Your pussy clenched rhythmically around his dick, and you heard him groan, the first truly uncontrolled sound he'd made.
His thrusts became erratic, chasing his own release. He buried himself deep inside you one final time, and you felt him come, his dick pulsing as he filled you with his cold seed.
For a long moment, neither of you moved. He stayed inside you, his weight pressing you into the mattress, his forehead resting against your shoulder.
Then, slowly, he pulled out. You felt his cum leak out of you, warm from your body heat despite how cold it had been going in.
He lay down beside you, pulling you against his chest. His hand rested on your stomach, fingers splayed possessively.
The silence stretched between you, comfortable in a way it rarely was.
Finally, he spoke.
"Why do you think you still have human qualities?"
The question hung in the air. You turned your head to look at him, finding his eyes already on you, studying your face.
"I don't know," you admitted quietly. "Your blood should have changed everything. Made me like you."
"It should have," he agreed. His fingers traced idle patterns on your skin. "But it didn't. Not completely."
"Do you have any theories?"
His expression was unreadable. "Several. None that make sense."
You waited, but he didn't elaborate. Instead, his hand moved to your chest, resting over your heart.
"Your heart beats like a human's," he said softly. "Steady. Warm. Alive in a way mine hasn't been for centuries."
"Is that why you keep me here?" you asked. "To study me?"
"Partly." His thumb brushed over your sternum. "But not entirely."
He didn't explain what he meant, and you didn't ask. Some questions, you'd learned, he wouldn't answer even if you pressed.
"We'll figure it out," he said finally, though he didn't sound entirely convinced. "Eventually."
"And if we don't?"
His arm tightened around you, pulling you closer against his cold body.
"Then you'll remain an anomaly," he murmured. "Mine to keep. Mine to understand."
The possessiveness in his voice should have frightened you. Maybe it did, a little.
But as you lay there in his arms, your warmth seeping into his cold skin, you couldn't quite bring yourself to pull away.
The question of why you were still warm lingered between you, unanswered.
And somewhere in the back of your mind, you wondered if maybe—just maybe—neither of you really wanted to find the answer.
Divider(s): @uzmacchiato