UNDERNEATH.ᐟ

UNDERNEATH.ᐟ

pairing ᝰ.ᐟ sister's bf! lee heeseung x reader

genre ᝰ.ᐟ smut

warnings ᝰ.ᐟ cheating, fingering, etc.

natty’s notes ᝰ.ᐟ part 2 of she’s right, mdni, hate comments will be deleted.

you don’t know how it happened—how you ended up like this, pressed into the armrest of the couch, your body tense with awareness. it wasn’t supposed to be like this. but somehow, heeseung had found his way right next to you, his presence suffocating, his warmth radiating off of him like a silent taunt.

your sister lay draped over his chest, her focus entirely on the movie playing on the tv, oblivious to the way his attention wasn’t on her.

it was on you.

your breath catches the moment you feel it—his fingers, featherlight, grazing against the exposed skin of your thigh. the touch is barely there, but it sends a ripple of heat through you, goosebumps rising in its wake. you swallow hard, your heart pounding as his fingers continue their slow, deliberate path, tracing lazy patterns against your skin.

heeseung acts as if nothing is happening, his eyes locked onto the screen, his face unreadable. but his fingers say otherwise. they move with intention, creeping higher, brushing just under the hem of your shorts.

you suck in a sharp breath, fingers curling into the fabric of the blanket draped over your lap, your body screaming at you to move—to stop this before it goes too far.

but you don’t.

because as much as you hate to admit it, a part of you is frozen in place, anticipation thick in your veins, waiting to see just how far he’s willing to go.

“heeseung—” you whisper, your voice barely audible, breath hitching as you feel the gentle but insistent tug of his fingers on the waistband of your shorts. your body tenses, heat pooling low in your stomach, torn between the fear of being caught and the undeniable thrill of his touch.

his eyes flicker to yours, dark and unreadable, his lips curling into the faintest smirk before he leans in just enough for his breath to fan against your ear.

“shh, baby…” he murmurs, voice low and teasing, his fingers toying with the elastic of your shorts, pulling it back slightly before releasing it, letting it snap softly against your skin. the action is subtle, but it sends a jolt through you, your pulse pounding in your ears.

your gaze darts toward your sister, still curled up against his chest, completely unaware of the illicit touches happening just inches away from her. her eyes remain glued to the tv, her face illuminated by the flickering glow of the screen, lost in the movie while you’re trapped in this dangerous moment with her boyfriend.

heeseung shifts slightly, angling himself closer, his fingers dipping just beneath the fabric now, skimming along the soft skin of your hip. his touch is slow, lazy, as if he has all the time in the world.

“you’re so tense,” he whispers, his voice barely above a breath. “just relax, baby… let me take care of you.”

your fingers dig into the couch, knuckles white, trying to ground yourself as the weight of the situation crashes down on you. this is wrong. so, so wrong.

but the way heeseung’s fingers move—the way his voice seeps into your skin like honey—makes it so damn hard to stop.

before you can fully process what’s happening, you feel it—his hand slipping under your shorts, fingers deftly pushing past the waistband of your panties. your breath catches in your throat, your entire body stiffening as his fingertips brush against your already-soaked folds. the touch is light, teasing, but the sensation sends a shiver through you, your thighs instinctively parting just enough to grant him access.

his fingers move slowly at first, tracing along your slit, gathering your slickness before pressing just a little harder. the faintest grunt slips from his lips, barely audible, but you hear it—feel the way his body shifts slightly, adjusting himself as if even just touching you like this is too much for him to handle.

“fuck…” heeseung exhales, his voice rough, almost strained.

his fingers continue their lazy exploration, circling around your entrance but never fully pushing in, his touch deliberate, torturous. he drags his fingers through your wetness, spreading it, his breathing growing heavier as he feels just how ready you are for him.

your nails dig into the cushion beneath you, your heart hammering in your chest as you risk a glance at your sister. she’s still nestled against him, completely unaware, lost in the glow of the movie playing on the screen.

but you’re not.

you’re drowning in the heat of his touch, in the way his fingers glide against you with practiced ease, in the way his breath grows heavier, hotter, with every passing second.

heeseung tilts his head slightly, his lips brushing against your ear as he whispers, “so fucking wet… all for me.”

your head tilts back against the couch, eyes fluttering shut as a wave of pleasure rolls through you. his fingers stroke your clit with an agonizing precision—slow, deliberate circles that send electric shocks pulsing through your core. the sensation is overwhelming, your thighs jerking slightly in response, but heeseung only tightens his grip, keeping you exactly where he wants you.

your breath comes in shallow pants, chest rising and falling with each teasing motion of his fingers. every stroke is a calculated push, a silent command for you to give in, to let go, to let him take you apart piece by piece.

you bite down on your lip, desperate to stay quiet, but then heeseung moves lower, his fingers gliding through your slick folds before dipping inside you. the stretch is slow, torturous, as he eases one, then two fingers into your heat, filling you inch by inch.

a muffled whimper threatens to escape, your body trembling as he curls his fingers just right, pressing into that sensitive spot that makes your stomach clench.

“so fucking good for me…” heeseung whispers, his breath hot against your ear, voice thick with lust. his fingers move in steady, deliberate strokes, pumping in and out of you, his thumb still working your clit in perfect rhythm.

the room feels unbearably hot, every nerve in your body hyperaware of his touch, the weight of your sister’s presence only making it all the more intoxicating.

“keep quiet, baby,” heeseung murmurs, smirking as he presses a kiss to the side of your neck. “or she’s gonna find out just how much of a mess you’re making for me.”

you clench helplessly around his fingers at his filthy words, a muffled whimper slipping past your lips before you can swallow it down. the heat in your stomach coils tighter, twisting into something unbearable as heeseung continues working you open, his fingers curling with calculated precision, pressing against that sweet spot inside you that makes your entire body tense.

just when you think you might be able to keep yourself under control, heeseung suddenly withdraws, leaving you empty for a brief, torturous second before pushing back in—this time with three fingers.

the stretch is intense, burning in the best way possible, your walls instinctively clenching around him as your back arches slightly. a sharp gasp rips from your throat, louder than you intended, the sound echoing in your own ears like a betrayal. panic surges through you, your sister still so close, and you barely have time to react before you’re slapping a trembling hand over your mouth, muffling your own pleasure.

heeseung doesn’t stop—if anything, he takes your reaction as an invitation. his pace quickens, fingers plunging deeper, fucking into you with a quiet desperation that makes your thighs shake. his free hand grips your inner thigh, keeping you open for him, making sure you take everything he gives you.

“that’s it, baby,” heeseung whispers against your ear, his voice dripping with amusement and arousal. “feel so fucking good squeezing me like that.”

your legs tremble violently as the pleasure builds, your entire body on fire, dangerously close to the edge. and the worst part?

you have to stay completely silent while he ruins you.

“naughty girl,” heeseung breathes against your ear, his voice laced with amusement and something darker, something possessive. his fingers never slow, plunging deep inside you, curling just right as he watches every desperate reaction spill across your face. “letting me finger fuck you while your sister is right here… you really have no shame, do you?”

his words make your stomach tighten, the coil inside you winding impossibly tight, threatening to snap at any moment. your breathing is uneven, ragged, your body trembling as his fingers continue their ruthless pace.

“should i even let you cum?” he taunts, his lips barely grazing your jaw as he whispers the cruel question.

your eyes fly open, desperate, pleading, as you meet his dark, hungry gaze. heeseung looks utterly amused, completely in control, reveling in the way you’re falling apart at his touch.

you nod furiously, your movements frantic, your entire body begging for release without a single word. your grip on the couch tightens, your free hand still clamped over your mouth, muffling the whimpers that threaten to spill out as the pleasure builds to a breaking point.

heeseung smirks, clearly enjoying your desperation. his fingers slow just enough to make you whine softly against your palm, your hips bucking in silent protest.

“hmm,” he muses, pretending to think as his thumb lazily circles your clit, sending another jolt of pleasure straight through you. “i don’t know, baby. do you really deserve it?”

“y—yes, heeseung—please…” you whimper softly, voice barely above a breath, laced with desperation. your head tilts back against the couch, eyes fluttering shut as your body completely surrenders to his touch. every nerve is on fire, every sensation heightened by the sheer risk of the moment, by the fact that your sister is still so close—completely unaware of how her boyfriend is ruining you right beside her.

your thighs tremble, threatening to snap shut around his hand, but heeseung doesn’t allow it. his fingers keep working you open, pressing deeper, curling with perfect precision as his thumb continues slow, teasing circles against your clit. the pleasure is overwhelming, stealing the air from your lungs, making it nearly impossible to stay quiet.

heeseung watches you with dark, hooded eyes, his lips curving into a wicked smirk at the sight of you coming undone for him. he leans in, his breath warm against your skin, his voice nothing more than a whisper against your ear.

“look at you,” he murmurs, his tone dripping with amusement. “so fucking desperate. you want to cum that badly, baby? even with her right here?”

you can’t even bring yourself to answer—only a shaky, breathless moan escapes as your fingers clutch at the fabric beneath you, holding on for dear life.

“please, seungie—i can’t…” you whimper, your voice trembling, barely coherent through the haze of pleasure consuming you. your entire body is wound tight, every muscle tensed as the pleasure builds higher, dangerously close to spilling over.

the hand that had been gripping the couch in a desperate attempt to ground yourself now flies up to your mouth, pressing firmly against your lips to stifle the moans threatening to slip out. your breaths come in short, ragged gasps against your palm, the heat of your own touch doing little to muffle the sounds completely.

your other hand, shaky and weak, reaches out blindly, searching for something—anything—to hold onto. it finds heeseung’s wrist, fingers curling around it in a silent plea. his skin is hot beneath your touch, his pulse steady, unbothered, in contrast to the absolute mess he’s turning you into.

heeseung smirks, clearly reveling in your desperation. his fingers don’t slow, still thrusting into you with that agonizing precision, curling just right, dragging against every sensitive spot inside you like he knows your body better than you do.

“can’t what, baby?” he whispers, his lips grazing the shell of your ear. “can’t take it? or can’t hold it in?”

his words only make it worse, make the coil in your stomach tighten even more, make your thighs shake as you struggle to stay quiet. heeseung chuckles, his free hand sliding up your thigh, squeezing lightly before whispering,

“then be a good girl and cum for me… but don’t you dare make a sound.”

his words are your undoing. the moment they leave his lips, the coil in your stomach snaps violently, pleasure crashing over you in thick, pulsing waves. your entire body tenses before completely unraveling, your back arching slightly against the couch as you fall apart on his fingers.

your hand clamps down tighter over your mouth, pressing so firmly against your lips that your knuckles turn white, desperate to keep yourself silent. a muffled whimper escapes anyway, swallowed by your palm as your walls flutter around his fingers, gripping them like a vice.

heeseung groans under his breath, feeling the way you gush around him, soaking his fingers, dripping down his hand. his movements don’t stop—he keeps thrusting, slower now, dragging out every last bit of your high, prolonging your pleasure until you’re trembling beneath his touch.

your thighs quiver uncontrollably, your muscles weak and useless as the aftershocks ripple through you. your free hand, the one clinging to his wrist, squeezes weakly, as if silently begging him to stop, to give you a moment to recover.

but heeseung doesn’t pull away immediately. instead, he lets his fingers linger inside you, feeling the way your walls still clench around him, your body twitching with sensitivity. his gaze flickers to your sister for a split second, ensuring she’s still lost in the movie before his eyes return to you—dark, satisfied.

finally—finally—he eases his fingers out of you, the slow drag making your breath hitch, your body still reeling from the high.

he doesn’t say anything at first. he just stares at you, watching the way your chest rises and falls, the way your lips part slightly behind your trembling hand, the way your thighs still quiver from the intensity of it all.

then, with slow, deliberate movements, heeseung lifts his fingers—glistening, coated in the evidence of your pleasure. the sight alone makes your stomach tighten, heat rushing to your cheeks as you watch, wide-eyed, unable to look away.

his expression remains unreadable, but there’s something dark, something dangerously smug in the way he parts his lips, slipping his fingers into his mouth with an agonizing slowness. his tongue flicks over them, savoring every trace of your slickness, his eyes still fixed on the tv as if this were nothing more than a casual indulgence.

but you see it—the way his chest rises just a little deeper, the subtle twitch in his jaw, the tension in his shoulders betraying the restraint he’s barely holding onto. he hums lowly, the sound barely audible over the hum of the screen, but you hear it, feel the vibration of his satisfaction curl in your stomach.

when his fingers finally slip free, shining with the wetness of his lips, heeseung exhales slowly, savoring the lingering taste like something he isn’t ready to let go of just yet. then, as if nothing happened, he lowers his hand, the movement unhurried, almost lazy, as he lets it fall onto his lap.

the room remains quiet except for the murmur of the tv, your sister still nestled against his chest, completely unaware of the sinful act that had just unfolded inches away from her.

your breath is uneven, your thighs still trembling slightly, your body betraying you as the ghost of his touch lingers, pulsing between your legs.

heeseung doesn’t look at you, doesn’t acknowledge what just happened—not outright. but his smirk deepens, his fingers tapping absently against his thigh, the motion slow, rhythmic, taunting.

and then, in a voice just above a whisper, meant only for you, he mutters, “that’s my good girl.”

natty’s notes ᝰ.ᐟ okay if you read my last one, act like it never existed, this is a lot better and i’m actually happy with how it turned out :))