Sibling Love

Author's Note: This story is inspired by c0p13r's "Sibling Snuggle" fanfiction.

The thunder was what woke Karin first.

Not the lightning -- she had slept through that initial flash, the one that turned the bedroom into a negative of itself for a split second, white tree branches etched against black. It was the sound that followed, a deep, rolling boom that seemed to originate from somewhere beneath the house, vibrating up through the floorboards and into her chest. It dragged her from sleep with a start, her heart hammering before her eyes were even open.

She lay in bed for a moment, listening. Rain lashed against the window in sheets, a steady, drumming roar. Water gurgled through the gutters overhead. Another flash of lightning bleached the room white, and she counted -- one, two, three -- before the thunder cracked again, closer this time, rattling the glass in its frame. She had never been afraid of thunderstorms, not really. There was something liberating about their fury, the way they made the world outside shrink to nothing. But tonight, the house felt too empty, the walls too thin, and the weight of the storm pressed down on her chest like a physical thing.

Beside her, Yuzu slept soundly, her breathing even and soft, her hair fanned across the pillow. A tiny line creased her brow even in sleep, the residue of the late-night studying she had done. Karin considered waking her -- Yuzu would come, she always came, her soft hands and softer voice a balm for any fear -- but Yuzu had been up late preparing for a test, her eyes heavy and her yawns wide, and she looked so peaceful that Karin couldn't bring herself to disturb her. Instead, Karin slid out of bed, her feet meeting the cool floorboards, the wood smooth and familiar beneath her soles. She would just get a glass of water. Maybe check on Ichigo.

The hallway was dark, the only light the occasional flicker of lightning through the window at the far end. Their father's door was open, as always -- Isshin's rule, born from some paranoid shinigami instinct about surprise attacks. Karin could hear his snoring, a rhythmic rumble from the depths of his chest that competed with the storm outside for dominance. She paused outside Ichigo's door, her hand hovering over the knob. The wood was cool beneath her fingers.

He wouldn't mind, she told herself. It was just for a minute. Just until the storm passed.

She pushed the door open slowly, the hinges barely whispering. Ichigo's room was exactly as she expected -- neat, organized, the bed against the far wall beneath the window, the faint outlines of his dresser and desk in the dark. He was asleep on his side, facing away from her, the blankets pulled up to his waist, one arm tucked under his pillow. Another flash of lightning illuminated the room in stark relief, and for a moment, Karin saw the curve of his shoulder—broad and solid like a man's, not a boy's—the line of his spine tapering to his waist, the sheer length of him stretching across the bed. Even in sleep he seemed to take up more space than she did, his body casting a long shadow across the sheets. He looked younger in that frozen second of light. Softer, but still so much larger than her.

"Ichi-nii?" she whispered.

No response. Just the steady rise and fall of his breathing, deep and even, the rhythm of someone completely untroubled.

Karin padded across the room, her bare feet silent on the floorboards, and slid under the covers on the other side of the bed, careful not to touch him. The mattress dipped slightly under her weight, the springs creaking a quiet protest. She lay on her back, staring at the ceiling, listening to the rain hammer the roof. The bed was warmer than hers, the sheets carrying the residual heat of his body. It smelled like Ichigo -- soap and clean cotton and something else, something warm and uniquely him that she had never been able to name. It wrapped around her like a second skin, comforting in a way she hadn't expected.

For a while, that was all it was. Comfort. The storm raged outside, water streaming down the window in rivulets that caught the occasional flash of lightning, but here, in her brother's bed, surrounded by his scent and the steady rhythm of his breathing, she felt safe. She closed her eyes, ready to wait out the worst of it.

And then Ichigo moved.

It was subtle at first -- a shift of weight, a sigh that was almost a word. He rolled onto his other side, the movement slow and unguarded, and his arm slid across her waist, heavy and warm, pulling her back against him. Karin stiffened, her eyes flying open. He was still asleep -- she was sure of it. His breathing hadn't changed, hadn't quickened. But his body was solid and warm against her back, his broad chest completely enveloping her slender frame, his arm spanning nearly her entire waist, pulling her against him like she was a doll to be tucked under his chin. The sheer size difference was startling—at 5'9" (175cm) he towered over her 4'6" (137cm) frame, and she could feel how much bigger he was, how his body completely surrounded hers, and the sudden intimacy of it stole the breath from her lungs.

"Ichi-nii," she whispered again, a little louder this time, a tremor creeping into her voice.

He murmured something, his face pressing into the back of her neck. His breath was warm against her skin, slow and even, and Karin felt a shiver run through her that had nothing to do with the storm. The sensation started at the base of her skull and traveled down her spine, settling somewhere low in her belly.

This was wrong. She knew it was wrong. She should push him away, should slip out of the bed and go back to her room before this went any further. But the warmth of him, the solidity of his body against hers, the way his arm held her with unconscious possessiveness -- it felt good. It felt safe. And the storm was still raging outside, rattling the windows and shaking the house on its foundation.

So she stayed.

She lay there, tense at first, every muscle coiled, waiting for him to wake up. But he didn't. He just held her, his breathing steady and deep, his body a warm curve against her back. Slowly, Karin relaxed into the embrace. She let her head rest against the pillow, let her body mold to his, her spine settling into the curve of his chest. His hand, resting on her stomach, was warm through the thin fabric of her nightshirt, and she could feel each individual finger, the weight of his palm, the slight calluses on his fingertips.

Another roll of thunder, closer this time, a crack that seemed to split the sky directly overhead, and Karin flinched. Without thinking, she pressed back against Ichigo, seeking the comfort of his solid frame. He responded in his sleep, his arm tightening around her, his hips shifting forward until they were pressed flush together, leaving no space between them.

And that was when Karin felt it.

A hardness, pressing against the small of her back. At first, she didn't understand what it was. Her mind fumbled for an explanation, rejecting the obvious. Then it shifted, pressing more insistently, nudging against her spine, and her thoughts caught up with her body. Heat flooded her cheeks, spreading down her neck. She knew what it was. She had taken health class. She knew about erections, about the body's automatic responses, about all of it.

But this wasn't morning. And Ichigo was asleep.

"Ichi-nii," she whispered, her voice shaky now. "Wake up."

He didn't. He just nuzzled closer, his face pressing into her hair, his hips rocking forward in a slow, sleepy rhythm that was barely conscious. The hardness pressed against her through the thin layers of fabric, and Karin's breath caught in her throat. It should have been disgusting. It should have been horrifying. But it wasn't. The warmth of him, the steady pressure, the way his body moved against hers with an instinctive, searching need -- it stirred something unfamiliar in her chest, a strange, electric thrill that made her skin feel too tight.

Her heart hammered against her ribs so hard she was sure he'd feel it. Her skin was hypersensitive, every nerve ending alight. She was acutely aware of every point of contact between them -- his arm around her waist, his chest against her back, his breath warm on her neck, his hips pressed to hers. And that hardness, that unmistakable proof of his body's response even in the depths of sleep, pressing against her like a question she didn't know how to answer.

Karin closed her eyes. She should move. She should get up. She should do something.

Instead, she shifted her hips, just a little. Just enough to feel the length of him more clearly. Just enough to make him groan in his sleep, a low, rough sound that vibrated through her back and into her chest.

His hand moved, sliding up from her stomach to her ribs. His fingers splayed, his thumb brushing the underside of her breast through the fabric of her nightshirt. Karin gasped, her body arching into the touch before she could stop herself. It was too much. It wasn't enough.

"Rukia," Ichigo murmured, his voice thick with sleep, the name barely coherent.

The word hit her like a splash of cold water. Karin froze, her eyes snapping open in the dark. Of course. Of course he thought she was Rukia. They were similar in build, in height. And Ichigo and Rukia were... whatever they were. More than friends, less than lovers, complicated in the way only shinigami relationships could be. Karin had seen the way he looked at her, the way he dropped everything when she called. She had heard him say her name in his sleep before, but never like this, never with his body pressed against hers and his hand on her breast.

She should have felt relieved. Should have been glad he didn't know it was her. But instead, a hot, sharp feeling twisted in her chest. Jealousy, she realized. Stupid, irrational jealousy.

Ichigo's hand moved again, cupping her small breast fully this time, his thumb circling her nipple through the fabric. It hardened under his touch, a tight, aching peak that pressed against the cotton of her nightshirt. Karin bit her lip to keep from making a sound. It felt so good. So wrong. So impossibly perfect.

His hips rocked again, harder this time, the hardness pressing insistently against the small of her back. Karin's body responded without her permission, a heat pooling low in her belly, a dampness gathering between her thighs. She was wearing only her nightshirt and panties, and suddenly she was acutely aware of how thin the fabric was, how little separated her skin from his.

"Ichigo," she breathed, not caring if he heard her, not caring if he woke up. She wanted him to know. She wanted him to wake up and see her and want her anyway.

But he didn't. He was lost in whatever dream he was having, his body moving against hers with a lazy, unhurried rhythm that was almost tender. His hand kneaded her breast, his thumb rubbing circles over her nipple until it was aching and stiff. His other arm tightened around her waist, holding her close as his hips rocked, the hardness rubbing against her through his pajama pants.

Karin gave in. She let her head fall back against his shoulder, let her body relax into his movements. She reached back, her hand finding his hip, holding him to her. She could feel the muscles of his thigh tense and release with each unconscious thrust, could feel the heat of him through the cotton of his pajamas, could feel the way his breath hitched when she pressed back against him.

It was wrong. It was so wrong. But it felt so good. The storm outside was nothing compared to the storm inside her, the thunder of her heartbeat, the lightning of sensation every time he moved against her.

His hand slid down from her breast, over her stomach, to the waistband of her panties. Karin's breath hitched. No, she thought. Yes. Please. Don't.

His fingers slipped beneath the elastic, and Karin's whole body went rigid. He was touching her there, in the most intimate place, and he didn't even know it was her. He thought she was Rukia. He was dreaming of Rukia.

And yet his fingers were clever, even in sleep. They found her slick and ready, sliding through the wetness with an ease that made her gasp. He made a soft, approving sound against her neck, a murmur of sleepy satisfaction, and one finger slid inside her. Karin choked back a moan, her hand flying to her own mouth. It was too much. It was everything. The sensation of being filled, even by just one finger, sent a jolt through her that made her toes curl.

"So wet," Ichigo murmured, his voice rough with sleep. "Rukia..."

The name was a knife in her heart, but the touch of his fingers was a balm. He added a second finger, stretching her, filling her, and his thumb found her clit, rubbing in slow, maddening circles that made her hips buck against his hand. Each pass of his thumb sent a pulse of pleasure through her, building in intensity, coiling tighter in her belly.

She was going to come. She was going to come on her brother's fingers while he dreamed of another woman. The thought should have horrified her, should have killed the feeling entirely. Instead, it sent a fresh wave of heat through her, a desperate, aching need that made her press back into him, seeking more.

"Ichi-nii," she gasped, her hand tightening on his hip. "Please..."

He didn't answer. He just kept touching her, his fingers moving inside her in a steady rhythm, his thumb working her clit, his hips rocking against her back. The hardness pressed against her, a constant, insistent pressure that she could feel through the layers of fabric. Karin could feel herself unraveling, the tension coiling tight in her belly, ready to snap.

And then, with a soft cry she couldn't hold back, she came. Her body shuddered against his, her inner muscles clenching around his fingers in long, pulsing waves. The pleasure washed over her in rolling surges, each one stealing her breath, until she was trembling and limp in his arms, her forehead pressed to the pillow, her breath coming in ragged gasps.

Ichigo groaned against her neck, his hips stuttering against her, his own release following hers. Karin could feel the damp heat of it through his pajama pants, a spreading warmth that soaked through the fabric. She could feel the way his body went slack against hers, spent and satisfied, his arm loosening around her waist.

For a long moment, neither of them moved. The only sounds were the rain against the window and their ragged breathing, slowly returning to normal. Then, gradually, Ichigo's hand withdrew from her panties. His arm around her waist loosened further. He shifted, turning onto his back, his breathing already deepening back into the rhythm of sleep.

Karin lay there, staring at the ceiling, her body still humming with aftershocks. What had she done? What had they done?

She should get up. She should clean herself up. She should pretend this never happened.

But her legs felt like jelly, her muscles loose and uncooperative. And the warmth of the bed, the scent of Ichigo beside her, the memory of his fingers inside her -- it all held her there, captive. The heat between her legs was a persistent ache, a reminder of how close they had come to something more, how her body had responded to him even while his mind was elsewhere.

Outside, the storm was finally beginning to pass. The thunder was distant now, fading into low grumbles that rolled across the sky. The rain softened from a roar to a gentle patter against the glass. Karin closed her eyes, listening to Ichigo's breathing, feeling the steady rise and fall of his chest beside her. Her hand drifted to her stomach, to the place where his hand had rested, and she pressed down gently, as if she could hold the warmth there.

Just as she was gathering the will to leave, Ichigo stirred again. He murmured something unintelligible, his arm reaching out in sleep to pull her closer. His hand found her hip, his fingers curling around the hem of her nightshirt. He pushed it up slowly, his movements lazy and dreamlike, exposing the bare skin of her thigh.

"Rukia," he breathed against her neck, his voice thick with sleep.

Karin froze. Part of her wanted to correct him, to push him away, to end this before it went any further. She had already let him do more than she should have. But a larger part -- the part that was still aching, still wanting, still curious -- stayed perfectly still. He thought she was Rukia. He was dreaming of Rukia. And she... she was going to let him.

His hand slid between her legs, fingers finding her panties again. He pushed them aside, his touch more confident this time, no longer fumbling. He traced her folds, finding her still slick from her earlier release, and made a low, satisfied sound.

"Want you," he murmured, his hips pressing against her backside. The hardness was there again, more insistent now, pressing against her through his pajama pants. She could feel the shape of him more clearly this time -- the length of him, the thickness, the way he strained against the fabric.

Karin's breath caught. This was it. The point of no return. She could still stop this. She should stop this.

Instead, she reached back, her hand finding the waistband of his pajama pants. She pushed them down just enough, freeing him. Her fingers closed around his length, and she gasped. He was hot -- hotter than she had expected -- and hard, and impossibly large. Her small hand could barely close around his girth, her slender fingers struggling to span the thickness of him. The size difference was shocking—she felt like a child trying to grasp something meant for adults, her hand dwarfed by his erection. The skin was smooth over the rigid flesh beneath, and she could feel every ridge and vein, could feel the pulse of his blood beneath her fingertips. She had never touched a man before, never seen one fully aroused. The reality of him was startling, almost overwhelming.

Ichigo groaned, his hips bucking into her hand. "Rukia," he whispered again, his voice rough with need.

He shifted behind her, his hand guiding himself to her entrance. The head of him nudged against her slick folds, and Karin tensed, expecting pain. She was a virgin -- she knew this would hurt. But Ichigo was gentle even in his sleep-drugged state. He pressed forward with a slow, steady pressure, the head breaching her in a single, careful push.

"Wait," Karin breathed, but the word was lost in the sound of the rain.

He pushed forward, slowly, steadily. Karin's eyes widened, her breath catching in her throat. There was pressure -- a deep, stretching sensation that bordered on burning -- but less pain than she had expected. She was still wet from before, still relaxed from her climax, her body open and ready in a way she hadn't prepared for. And Ichigo, for all his size, was careful, his movements measured even in sleep. She could feel the sheer scale of him—the way her much smaller body had to accommodate him, the feeling of being stretched open beyond what she thought possible.

He filled her inch by inch, and Karin bit her lip to keep from crying out. The feeling was overwhelming -- the sheer size of him, the way he stretched her, the sense of being completely, utterly occupied. She had never imagined it would feel like this. Never imagined he'd be this big, that her body would be able to take all of him.

When he was fully sheathed inside her, he stilled for a moment, breathing heavily against her neck. Karin could feel every inch of him, could feel the way her inner walls gripped him, adjusting to his presence. It was almost too much. Almost.

"Fits," Ichigo murmured, his voice full of sleepy wonder. "You fit me perfect."

Karin's heart clenched. He was talking to Rukia, not her. But the words still sent a thrill through her. She did fit him. Despite her inexperience, despite her virginity, her body had accepted him. The ache was fading, replaced by a strange, full sensation that was almost... pleasant.

Then he began to move.

Slowly at first, just shallow thrusts that made her gasp. Each withdrawal and re-entry sent a ripple of sensation through her, building on itself. His hand found her breast again, kneading it through her nightshirt. His other arm tightened around her waist, holding her close as his hips rocked against her in a rhythm that was ancient and instinctive.

The rhythm built gradually, his unconscious thrusts finding a steady, unhurried pace. Karin found herself moving with him, her body learning the cadence of his body. The initial discomfort faded completely, replaced by a deep, pulsing pleasure that seemed to originate somewhere behind her navel. Each stroke rubbed against something inside her that made her toes curl, that made her breath come in short, sharp gasps. Her inner walls began to contract around him in rhythm with his thrusts, a response she hadn't known her body was capable of.

It was different from what she had felt with his fingers. Deeper. More profound. She could feel him everywhere -- filling her, stretching her, claiming her in a way that went beyond the physical. And he thought she was someone else.

The thought should have hurt. Should have made her pull away, made her feel used. But instead, it freed her. She didn't have to be Karin, his sister. She could just be a body in the dark, a warm presence in his bed. She could lose herself in the sensation without worrying about what it meant, without worrying about what came after.

Ichigo's thrusts became harder, more urgent. His breathing was ragged against her neck, his fingers digging into her hip hard enough to bruise. Karin could feel the tension building in him, could feel the way his muscles coiled with each stroke, the way his rhythm was beginning to falter.

She wasn't going to come. The pleasure was there -- a constant, building pressure that coiled in her belly -- but it stayed just out of reach, a horizon she couldn't quite reach. She was too new to this, too overwhelmed by the novelty of it all. Her body was still adjusting to the feel of him, still trying to process the reality of what was happening.

But Ichigo was close. She could tell by the way his breathing hitched, by the way his rhythm stuttered and faltered. His arm tightened around her almost painfully, his hips driving into her with a final, desperate urgency.

Then he came.

Karin felt it -- the sudden rush of heat inside her, the way his body stiffened and shook against her back. He groaned, a raw, guttural sound that was nothing like his usual voice, a sound dragged from somewhere primal. His hips jerked through the last few thrusts, spilling himself deep inside her in long, pulsing waves that seemed to go on and on. She felt every pulse, felt the warmth of his release filling her, and something about that feeling -- of being claimed, of being filled -- made her chest ache with an emotion she couldn't name.

For a long moment, neither of them moved. Ichigo's breathing was ragged against her neck, his body heavy and spent against hers. Karin could feel the wetness between her legs, the sticky warmth of his release seeping from where they were joined. The reality of what they had done settled over her like a blanket, heavy and inescapable.

Slowly, carefully, Ichigo withdrew from her. He made a soft, contented sound and rolled onto his back, his breathing already deepening back into sleep. Within seconds, he was out again, lost in whatever dream had brought them together, his face slack and peaceful.

Karin lay still, her body tingling with sensation. The place between her legs felt empty now, sore and stretched. She could feel him leaking out of her, a warm trickle that soaked the sheets beneath her. But there was also a strange, persistent ache -- a hollow feeling, a sense of being left unfinished, of wanting more.

She should feel disgusted. She should feel guilty. But all she felt was... amazed. Amazed that it had happened. Amazed that she had taken all of him. Amazed that it had felt so good, so right, even with all the wrongness of it.

The storm was completely gone now. The rain had softened to a whisper against the window. The only sound was the soft patter of water and Ichigo's steady breathing. Karin knew she should leave. Should slip out before he woke up and realized what had happened.

But for a few more minutes, she stayed. She let herself feel the warmth of his body beside her, let herself remember the feel of him inside her. The tingling between her legs was a constant reminder, a promise of something she now knew existed. She pressed her thighs together, feeling the sensitivity, and a small shiver ran through her.

Finally, with a deep breath, she slid out of bed. The air was cool against her skin where his warmth had been, and she shivered. Her legs were shaky, and she had to steady herself against the nightstand, her hand gripping the edge until her balance returned. She pulled her nightshirt back down, wincing at the wetness between her legs, at the trickle that escaped her as she stood. She would need to clean up before going back to her room.

She looked back at Ichigo, sleeping peacefully in the dim light. He looked younger in sleep, the usual scowl smoothed from his face, his features relaxed and open. He seemed even larger in the quiet darkness, his frame taking up most of the bed, his long legs stretching toward the footboard. He had no idea what they had just done. No idea that his little sister had just given him her virginity in the dark, while he dreamed of someone else.

The thought should have made her cry. Should have made her sick. But instead, it made her smile. A secret smile, just for herself, in the dark of his room.

She padded quietly across the room, her bare feet silent on the floorboards, pausing at the door for one last look. Ichigo hadn't moved, hadn't stirred. He was still lost in his dream, still murmuring softly, his hand reaching across the empty space where she had been.

Karin slipped out of the room, closing the door silently behind her. The hallway was dark and quiet, the only sound the distant drip of water from the eaves. She made her way to the bathroom, her steps careful on the cool floorboards, the ache between her legs a constant, vivid reminder of what she had done.

As she cleaned herself up, washing away the evidence of their joining, she felt that same tingling between her legs. That same wanting. She knew she should feel guilty. Should feel ashamed. Her brother's cum, washing down the drain. Her virginity, given to a man who hadn't even known he was taking it.

But all she felt was... curious. Curious about what it would be like if he knew it was her. Curious about what would happen if they did it again. Curious about the feeling that was already building in her chest, the same feeling that had made her stay in his bed instead of leaving.

She dried herself off and slipped back into her own bed, careful not to wake Yuzu. The sheets were cold compared to Ichigo's, the bed empty and lonely. She curled onto her side, pulling the blanket up to her chin, and stared at the wall.

Karin closed her eyes, listening to the soft sound of the rain. Her body still hummed with the memory of him -- the feel of his skin, the weight of his body, the way he had filled her so completely. She pressed her hand between her legs, feeling the residual warmth, and a small sigh escaped her lips.

She knew she should forget this ever happened. Should lock it away in some dark corner of her mind and never think of it again.

But as she drifted off to sleep, her fingers tracing the place where he had been, she knew with a certainty that both terrified and excited her that this was just the beginning.