12 DAYS OF CHRISTMAS MASTERLIST | 2025.
@12daysofchristmas
[A03] [Fanfiction.net] [Wattpad]
Thaw (3.6k words)
Obanai Iguro x Reader
summary: You thought challenging your mentor, Iguro, to a snowball fight would bring out his playful side. Technically, it does—right up until you end up tangled in the snow, tangled in feelings, and learning that even the most reserved hearts have a breaking point. Especially when winter makes everything feel so brand new.
warnings/themes: Reader Insert, Hashira!Reader, Snowball Fight/Play Fighting, Mentor/Student Relationship, Slow Burn, Mutual Pining, Emotional Repression, Self-Doubt/Hatred, First Time Together, Hurt/Comfort, Power Dynamics, Rough Sex (but also gentle at the same time in a way), Vaginal Sex, Clothed Sex, Sex in the Snow, Feelings Realization/Confession, Aftercare, Bathing/Washing, Intimacy, Character Development, Vulnerability, Canon Divergence.
The storm that sweeps the Butterfly Mansion is the kind of snow that seems to swallow sound itself, layering every roof, every pine bough, every stone with a depthless hush. The garden, transformed by storm, glitters with the clean, crystalline magic of a story you half-remember from your childhood. Your boots crunch through powder, scattering flakes. The day’s chores have already been abandoned—everyone else hiding from the cold, leaving the outside world for ghosts and winter birds.
But Iguro is here, as he always is: precise, upright, a thin black line against the white. Kaburamaru rides his shoulder, tongue flicking as if reading the air for omens. The wind toys with the edge of Iguro’s striped haori; his eyes, mismatched and watchful, flick to you and away again. You’re new to the Demon Slayer Corps, still a little soft around the edges, and for reasons you haven’t quite puzzled out, Iguro was assigned as your mentor.
He calls it training, but lately it feels like something else—he’s become almost overprotective, his presence a constant shadow as the two of you have grown closer. Even standing still, he seems wary, braced for something heavier than snow.
You wave, the wool cuff of your coat slipping back to reveal cold-reddened knuckles. “It’s beautiful, isn’t it?”
Your winter uniform does its best—heavy coat belted tight, but your skirt brushes your knees, and the dark stockings beneath aren’t quite a match for the bite of the wind. A pale scarf wraps your neck, and stray flakes melt against the skin just above your collar.
He doesn’t answer at first, just shifts his weight, gaze skating from your flushed cheeks to your bare thighs and back again. “It’s cold,” he mutters, voice muffled behind his bandages. “You’ll catch a chill, out here in that.”
You roll your eyes, stomping your boots for effect. “You think I’m that fragile, Iguro-san?”
His lips twitch behind the gauze. “I think you’re reckless.”
You reach for a handful of snow—light and powdery, perfect for mischief. Your gloved hands shape it, and you lob it gently toward him. The snowball arcs, striking his sleeve. Iguro doesn’t flinch, but you notice the way his fingers tighten, how Kaburamaru lifts his head.
You smile, pushing him. “Come on—just one throw. Or are you scared you’ll lose?”
A faint, unimpressed sound. “Games are for children.”
You ignore him, throwing another snowball; this one just misses his hip. “You’re always so serious,” you tease. “Live a little.”
Iguro watches you, eyes narrowing in that assessing way—like he’s measuring your intent. “You think provoking me is wise?”
Trying not to giggle, you answer with a third snowball. This time, he moves: a swift, reflexive sidestep, faster than most people could track. The snow whizzes past, but a single flake lands on Kaburamaru’s nose; the serpent blinks, offended.
“Poor Kaburamaru,” you call, “He didn’t deserve that.”
Iguro flicks the snow away from Kaburamara, his care at odds with the sharpness in his voice. “You’re insufferable.”
You grin, undeterred. “Am I?” Then, in a burst of bravado, you dart behind a snow-laden shrub, breath puffing clouds. “Then do something about it!”
For a moment, nothing. Then: the crunch of boots as Iguro begins to move, not in a rush, but in a patient, predatory circle—herding, not chasing. His gaze never leaves you, even as he stoops, gathers a precise handful of snow, compacts it with a measured efficiency.
You pop up, throw—and miss. He doesn’t. His snowball clips your arm with enough force to sting, cold seeping through the fabric. You yelp, laughing, as you scramble again, behind a low stone wall.
“Give up?” he calls, a thread of amusement curling through his words, so faint you almost doubt you heard it.
“Ha, not a chance!” You peer over the wall. He’s watching, waiting, a hint of irritation behind his eyes. You throw again, and again—both go wide. Iguro’s next two are perfect: one explodes at your feet, the other bursts on your shoulder.
You surrender to drama, falling back in the snow with a wail. “Mercy!”
He steps closer, standing over you, one eyebrow raised. “Finished already?”
“Never,” you say, and quickly roll to your knees. You lunge, a handful of snow aimed at his stomach. This time, he’s caught off-guard—your hand lands cold and wet against his haori.
The moment hangs, suspended, breath turning to frost between you.
Iguro shakes his head, scattering snowflakes from his hair as he looks down at you. There’s an unfamiliar light in his eyes—a sharpness threading through the moment, walking the line between levity and something that bites. “You’re persistent.”
“Someone’s got to make you smile,” you say, boldly, “even if it’s only once a year.”
His mouth twitches again. “Tch. Keep this up, and you’ll end up as snake food.”
A fresh volley: you, scrabbling for snow; him, faster, his throws impossibly accurate, always forcing you back, always landing where they’ll sting but never hurt. It’s a dance—he doesn’t give you room to breathe, doesn’t let you hide. The rest of the world drops away—just snow in your lungs, your heartbeat, and the soft stalk of his footsteps.
The tension rises—light at first, then charged, like static in the winter air. Each near-miss becomes an excuse for a laugh, a yelp, a taunt. Every glance lingers longer. Your cheeks burn, not from cold, but from the heat in his gaze each time you dodge, the way his mouth quirks beneath his bandages, as if he can’t decide if he’s angry or bemused.
Kaburamaru, caught up in the chaos, loops from shoulder to wrist, flicking his tongue angrily at you. Iguro finally manages to corner you, forcing you back against the trunk of a tree. His breath mists the air; yours comes short, chest heaving from laughter and effort.
He leans in, so close you feel every exhale stir the cold air between you. “Had enough?”
You’re already shaping another snowball behind your back. With a flash of mischief, you lean in as if conceding—then reach around and slap it squarely against his back, never breaking eye contact. “Not until you surrender.”
He catches your wrist—stupidly fast, his grip firm enough to bruise. Snow falls from your glove. You twist, trying to break free and dart away, but he’s stronger; his thumb presses lightly over your pulse, always checking.
He stares at you, mismatched eyes smouldering. “Do you ever give up?”
You grin, unrepentant. “Not when I know I can win.”
Neither of you moves. Kaburamaru curls in silent witness.
Then, wordless, Iguro shifts his grip, tugging you forward. The world tilts; you stumble into him, his body caging yours with a careful violence that feels more protective than dangerous.
“You’re reckless,” he mutters again, tone caught between scolding and concern. “If this were actual combat, you’d be bleeding in the snow by now.”
“Ugh. It’s not, Iguro-san. You’re impossible,” you mutter, unable to keep the edge from your voice. You drop your gaze, disappointment curling in your stomach. Just when it felt like he might finally let his guard down, he pulls you right back into teacher and student—turning what felt real into another lesson.
He hesitates, something unreadable flickering in his mismatched eyes. The space between you thrums with things unsaid, and you sense his gaze searching your face—catching, maybe, on the disappointment you can’t quite hide.
Your smile falters, but you force it back, determined. If he’s going to pull away, you won’t let it be so easy. You tip your head, letting your tone turn playful again—one last invitation.
“Finish it, then,” you whisper, daring. “If you can.”
The snow keeps falling.
Not the gentle drift of earlier, but thick, intent flakes tumbling fast enough to blur the world into motionless white. The garden feels suddenly sealed off, as if winter itself has decided to hold its breath. Beneath the low sweep of the pine branches, you and Iguro are half-sheltered from the storm, the tree’s canopy gathering snow in its boughs above.
He stays close—too close—one hand still locked around your wrist, the other braced beside your shoulder against the tree. His body blocks the wind entirely; the cold pushed back by the heat radiating from him.
“You don’t know when to stop,” he says, low and controlled. His thumb presses into the sensitive hollow beneath your wrist—a silent reprimand, making his disapproval clear.
You tilt your head, snow dusting your lashes. “Fine. You caught me.”
He fixes you with that gold-and-green stare, harsh and unblinking. “I let you run.”
Kaburamaru shifts, coils tightening along Iguro’s collar, as if sensing a change in his master’s posture. The serpent’s tongue flicks, restless.
Iguro exhales slowly through his nose, the sound muffled behind the gauze. His jaw clenches; you see the muscle jump, see the battle being fought entirely inside him.
“This,” he says, leaning in until his forehead nearly brushes yours, “is exactly why I avoid indulging you.”
Your breath fogs between you. “...Because you secretly enjoy it?”
For a heartbeat, he says nothing.
His free hand slides from the tree—to your collar, fingers curling into the fabric with sudden intent. He doesn’t pull. He waits, eyes locked on yours, searching.
Your breath catches. You can’t tell if he’s about to lecture you again, or simply done with your nonsense. You certainly don’t expect anything else. Still, you don’t look away—bratty, challenging, determined not to flinch first, even as your heart stutters in your chest.
Then, something inside him snaps—not loudly, and not all at once—but with the soft, terrifying certainty of restraint finally giving way.
He drags you, forward and down, turning in one fluid motion so your back hits the snowbank instead of bark. Powder explodes around you, melting snow bites through your clothes, stealing your breath in a sharp gasp. Before you can react, he’s over you, knee braced between yours, hand planted beside your head, his weight pinning you without crushing.
“You don’t get to test me like that,” he says, voice roughened, darker than you’ve ever heard it, “and expect me to remain polite.”
His other hand follows you down, catching your chin between his fingers.
Not gentle. Purposeful.
Your pulse skids. For a dizzy second, you think he might actually be angry—cold, strict, every inch the stern Hashira you know from drills and discipline. But his face is close enough to blur, eyes searching yours for something even he can’t name. You can feel it through layers of fabric, through the tremor in his breath, through the tension wound tight beneath his skin, and suddenly you know—this isn’t just discipline, it’s something messier. He’s wrestling with himself as much as with you.
“Do you understand me?” He says, sternly.
You meet his gaze, heart thudding. Maybe it’s reckless, but you refuse to be cowed. Slowly, you reach up, fingers threading into his hair, damp and tangled with melting snow.
He flinches, but doesn’t pull away. For once, you have the power.
A smile ghosts across your lips, sly and a little sad. “You don’t even understand yourself, Sensei.”
The words hang between you, suspended and fragile. Iguro doesn’t move, snow settles in your hair and his. You watch his eyes widen, confusion and something unguarded flickering across gold and green. His grip on your jaw slackens, not quite trusting himself.
Carefully, you reach up, your gloved thumb brushing the edge of his bandages. His breath hitches. His whole body goes taut. You slip the cloth down, just enough to bare his mouth, the ragged line of his scars. You trace your thumb lightly across his cheek, taking him in.
“You’re so handsome,” you whisper, meaning every word.
The sound he makes then is low, broken, torn from somewhere deep in his chest. He hesitates only a beat longer, then surges forward, mouth crashing to yours—no hesitation now, no careful testing. The kiss is fierce, claiming, all teeth and heat, your fingers tangled in his hair, snow melting between your palms. You taste winter, and want, and a hunger he can’t hide any longer.
His hand slides from your chin to your throat, feeling the frantic flutter beneath your skin.
A grounding touch. A possession.
He breaks the kiss only to breathe against your mouth, words rough and spilling. “You’re freezing.”
“Then warm me up,” you manage, breathless.
That earns a sharp huff of laughter—bitter, disbelieving. “Reckless,” he mutters again, but his body gives him away, lowering closer, shielding you completely from the wind. Snow gathers in the hollows of his shoulders, melts along the lines of his spine.
His mouth leaves yours, trailing heat along your jaw, your ear, your throat. Each kiss is deliberate, almost punishing in its intensity, as if he’s moulding you through pressure and breath. His palms slide down your sides, fingers splaying at your waist, anchoring you firmly into the snow.
You arch, instinctive, a soft sound slipping from you before you can stop it.
It’s what breaks the last of his restraint.
He groans—low, feral—and presses closer, his body fitting against yours with devastating precision. The cold is everywhere except where he touches you, where heat blooms and spreads, drowning out winter entirely. You’re dimly aware of Kaburamaru shifting away, giving space, of the garden dissolving into nothing but sensation. Snow melts beneath you, dampening your clothes, turning the ground slick and unforgiving.
His hands are everywhere, impatient now—fumbling with the buttons of your coat, tugging it open, baring your body to the winter air for only a breath before he covers you again. His fingers find the hem of your skirt, shoving it up, his palm running along your thigh, rough and hungry, the contrast of cold air and his feverish touch sending sparks up your spine.
His movements are urgent—barely controlled. He shifts, adjusts, positions you with a dangerous confidence, his dominance written not in words but in the way he takes space, the way he demands your attention with every press of his body.
He cups the back of your thigh, pulling you closer, settling between your legs. You feel him, hard and insistent through his uniform—one hand freeing himself, the other tugging at your underwear, working them down just enough.
“If you look away now, I might let you go,” he murmurs against your ear, voice shaking. “So don’t.”
You wouldn’t even if you could.
You reach for him, guiding him into place. When he finally presses inside, the world stops—a stinging, breathless ache as he fills you, your body clinging to his. His eyes never leave your face—watching every breath hitch, every involuntary response. Every time your body reacts, his grip tightens, satisfaction flaring dark and hot in his gaze. He’s unravelling, but he’s still watching, still careful in the only way he knows how.
He starts to move—shallow at first, then deeper, each thrust pushing you down into the snow, grinding you against the muddied earth. The friction is raw, burning where you’re joined, burning where his mouth finds your throat, your collarbone, your lips. Your nails bite into fabric at his back, clinging as pleasure builds, heat flooding outwards from where your bodies meet.
The world narrows.
There is only white sky above you, falling snow blurring the edges of everything, and Iguro—heat and weight and need—moving with a rough urgency that steals thought entirely. His breath is ragged now, the careful cadence gone, replaced with fractured exhales that fog the air between you.
Iguro presses his forehead to yours, eyes squeezed shut, as if the act of looking has become too much. His voice, when he speaks, is wrecked.
“I shouldn’t—” He stops, swallows hard. “I don’t lose control.”
You cup his face, thumbs brushing the edge of his bandages. “You’re allowed.”
That’s all it takes.
The tension leaves him all at once, a shudder tearing through his frame as he gives in completely—his hips driving into you, holding you so tight you can hardly breathe. The pleasure breaks over you sharp and sudden, your body arching beneath him, his name on your lips, lost to the snow. He buries himself deep, growling, as he pulses within you, trembling and clutching.
Snow muffles the sound of his breath breaking, the way his body tenses and finally stills against yours.
The snowstorm continues relentlessly, slowly filling the marks you’ve made in the snow. Iguro remains over you, chest rising and falling heavily, hands still braced like he’s afraid you’ll disappear if he lets go.
Eventually, he shifts—impossibly careful now—pulling your coat tighter around you, tucking stray fabric back into place with hands that still shake. He avoids your eyes, shame creeping back in where ferocity once lived.
“That was…” He stops, jaw tight. “…improper.”
You laugh quietly, warm despite the cold. “You won.”
His mouth twitches despite himself.
He helps you up, one hand never leaving your waist, guiding you back inside. As you walk, snow crunching beneath your boots, he stays close—shielding, watchful, silent.
Inside the Butterfly Mansion, the silence is almost holy. Iguro leads you down the hall, never quite letting go, the heat of his palm at your waist a silent tether. Snow clings to your lashes and hair, and your stockings are soaked through, boots leaving muddy tracks on the polished wood.
He pauses only to take a steadying breath, then ushers you into the small bathing room. The old metal tub sits in the corner, half-shadowed. Iguro busies himself without a word, drawing water and setting it to heat, the rhythm of his movements precise and strangely tender. His hands, still trembling, untie your coat, peeling off layers damp with snow and earth. He averts his eyes as he helps you step out of your ruined stockings, but you catch the faint flush beneath the edge of his bandages.
He lays out a towel, then tends the small stove, coaxing it to life, the metal groaning as the water warms. You sink onto a stool, arms wrapped around your knees, the room filling slowly with steam and the crackle of pine wood. For a while, there is only the whisper of water, the faint hiss of snow melting on the eaves. Every so often, you glance over your shoulder. Iguro is all angles and shadows, his gaze fixed on his work, but you sense the war inside him—a thousand things unsaid.
When at last the bath is ready, he turns away so you can slip into the steaming water. It stings at first, the heat burning away the last traces of cold, and you exhale slowly, watching the surface swirl around your legs.
He sits across from you, posture rigid, hands folded tight in his lap.
You break the silence, voice soft. “You don’t have to look so guilty, you know.”
He stiffens, fingers twitching. “It was… wrong. I shouldn’t—” He stops, jaw tight, and shakes his head.
You smile, letting your gaze linger on his. “I wanted it. All of it.”
He looks at you then—truly looks, heterochromic eyes wide and uncertain. “You don’t know what you’re saying.”
“I do,” you insist, your voice barely a whisper above the splash of water. “I know you think you’re…” You search for words, find only truth. “Iguro-san, I’ve never felt safer. Not with anyone.”
Something in him softens—a line at his mouth, the tension in his shoulders. He looks away, staring at the snow caught on the windowsill. For a while, you sit together in silence, watching the snowfall, letting the warmth soak in.
“I love winter,” you say, finally, a smile curling on your lips. “It makes everything feel new. Like anything could happen.”
Iguro glances at you, the faintest smile breaking through—gone almost as soon as it appears. “You’re too gentle for this world,” he murmurs, but his tone is softer than the words, as if he’s afraid of the world making you any harder.
You laugh, sinking a little deeper into the bath. “Then it’s a good thing I have you to look out for me, isn’t it?”
He doesn’t answer at first. You watch his hands flex. Then, almost shyly, he rises and comes to kneel beside the tub. His movements are careful as always, but this time there’s no hesitation as he dips a cloth into the hot water and begins to wash you, tracing slow, reverent circles over your skin. The steam curls around you both, cocooning you from the winter beyond the paper walls.
His touch is nothing like the storm of before, and you close your eyes, letting yourself melt under his hands. There are no words—just water, warmth, and the slow, steady rhythm of care.
“Insufferable,” he mutters. He shakes his head, but you hear the fondness there, so rarely given, so fiercely kept.
You reach for his hand beneath the water, linking your fingers with his. In the silent peace of the bathhouse, with the storm beyond and the heat blooming between you, you think you could love winter forever—if it always ends like this.
When your collection of Zenitsu Demon Slayer merch is growing rapidly, but they can't guard their manga because you promised your sister that you would buy the manga ONLY AFTER watching the movie in the theater (premier in September), so they just stand on a random shelf, guarding manga that isn't theirs 💔
