The sister's eyes flutter open, her gaze drawn to her brother's rhythmic breathing. She watches as his chest rises and falls, her mind wandering to the forbidden fruit that lies before her. Her hand trembles as she reaches out, her fingers tracing the outline of his cock through the thin fabric of his boxers. She can feel it twitch at her touch, her own body responding with a surge of wetness. She knows she should stop, but the allure of the taboo is too strong, and she finds herself unable to resist the urge to explore further.