Like A Puzzle, Perfect Fit (Firefly, Simon/River.)
Adult & incest-y/tamcest-y. You've been warned :)
Dark eyes, dark hair, pale skin. His baby sister writhing underneath him, wild and carefree and perfectly-imperfectly herself. His name on her lips and his lips on her throat, marking her, claiming her, and her nails scratching across his back.
She's hot and wet and their bodies fit together like puzzle pieces; hers clings to his and he breathes her name against her skin like a prayer, her voice echoing in his ears. Neither of them know what she's saying. Neither of them care.
He kisses her to stop her saying anything at all and she moans as he thrusts inside her -- fingers clutching at his shoulders, body arching into his -- crying out his name as she shakes and trembles.
His body responds to hers until he's aware of nothing else, and they're left lying, breathless, tangled in sheets and each other.
He thinks he should tell her they can't do this again.
He doesn't.
"Do you believe we'll go to hell?" she asks absently, as she curls against him and closes her eyes.
She has one hand over his heart and he pulls her closer. Thinks about pushing her away.
His baby sister.
He can't answer her.