After waking up in the middle of the night feeling thirsty, you make your way downstairs to get a drink of water.

Reaching the bottom of the steps, you hear a soft, strange cry. A tender female voice drifts in from the next room, barely audible above the low hum of the AC. You peer around the corner and see your sister Riko, wearing only an oversized t-shirt and lying face-first on the couch with her butt up in the air. The t-shirt is bunched around her upper-torso, leaving her lower half completely exposed.

Both of her arms are reaching down between her legs, with her right hand moving a sharpie in and out of her dripping pussy, and her other desperately rubbing the top of her pussy.

There's another moan, more distinct now that you're closer but still muffled as you see she's moaning into the couch cushions to dampen her voice. Most of her face is hidden, but you can see her eyes are glazed over in a sexual frenzy.

SNAP

The floor settles slightly under your foot as you shift position, leaning around the corner to look more closely.

She jerks her head in your direction. Seeing you there, her eyes widen and she freezes, her slick grip slipping from the marker enough that it pushes out of her onto the couch, a trail of fluid dripping down after it.

You swallow hard and look away, feeling your own cheeks flush red with embarrassment. You clear your throat and mumble an apology before hurrying back upstairs to the safety of your room. Closing the door behind you, you collapse onto the bed, a mixture of confusion, arousal and fear coursing through your body.

The thump of footsteps on the stairs draws your attention back towards Riko as she storms into your room, her face contorted with anger. "What the hell was that about?!"

Riko looks at you incredulously. "You saw me... didn't you? You saw what I was doing!" Her voice cracks with emotion as she struggles to contain her anger and shame.

Riko's eyes narrow as she steps closer to you, her chest heaving with each labored breath. "Then why did you come down here? Why didn't you just leave me alone?" The anger in her voice begins to give way to hurt and fear.

"Oh," she says quietly, her shoulders slumping. "I... I didn't know what else to do. I've been so horny lately, and it just took over." She looks down at the floor, unable to meet your eyes. "I'm sorry for freaking out on you. I shouldn't have done that in front of you."

There's a long pause as she continues to stare at the carpet, her breathing starting to steady again.

Riko looks up at you, her expression pained. "No... I didn't," she whispers. "But it feels so good..." Her voice trails off as she shivers slightly. "I can't seem to get enough of it." She pauses, then asks in a small voice, "Do you... do you ever feel like that?"

There's an awkward silence for a moment before she continues, her voice even quieter. "What if we... we could help each other? Maybe..."

"I don't know," Riko says softly, chewing on her bottom lip. "It just feels so good... and I can't really do it anymore unless..." She trails off, not wanting to finish that thought aloud. "What if we could... you know?" Her eyes flicker up towards your face, hopeful but scared at the same time.

Riko's eyes dart around the room before settling back on yours. Her cheeks flush pink as she whispers, "What if we... you know? Touched each other?" She takes a shaky breath, her heart racing in anticipation of your answer.

There's another silence, even more awkward than the last one, but somehow it doesn't feel quite as heavy between the two of you now. It feels almost like... maybe there could be something here worth exploring. Something real and true and not just for pleasure alone.

Riko's cheeks flush even darker as she nods eagerly, her body tense with anticipation. "Yeah... like sex." Her voice trembles slightly at the word, but there's no denying the excitement in her eyes. "I mean, if you want to..."

Riko takes a step closer to you, her breath hot against your ear as she whispers, "And you're my brother." She gently places a hand on your thigh, feeling the muscles tensing beneath her touch. "We could make each other feel so good... and no one would ever know." Her free hand moves up to stroke your cheek, her thumb tracing circles around your bottom lip.

There's another pause as she looks into your eyes, searching for any sign that you want this too.

Riko's heart races as she whispers back, "I know it's wrong... but I can't help how much I want this." She pulls you closer by the hand on your thigh, her body pressing against yours. "Please, let's just do it. It'll be our secret." Her breath is hot and ragged against your skin, and her scent fills your nose: a heady mixture of arousal and innocence that drives you wild with desire.

Riko bites her lip in thought, hesitating for a moment before nodding slowly. "Okay... I guess we could use something else..." She pulls away from you slightly and reaches down to unbutton your pants, sliding them off along with your boxers in one smooth motion. Her hand encircles your erection, feeling it twitch in her grasp as she looks up at you, hopeful but uncertain.

Riko looks at you uncertainly before nodding slowly and moving her hand away from your crotch. "Okay, I guess we'll just have to be careful then." She takes a deep breath and climbs onto the bed beside you, straddling your hips with her wet folds pressed against your erection. With shaking hands, she reaches down between your bodies and guides you towards her entrance, slowly sinking down onto your throbbing length.

Her moan echoes through the room as you both sink deeper into this forbidden act.