In the confines of their shared room, the young brother finds solace in the forbidden, his hand wrapped around his stiff cock. He strokes slowly, eyes closed, lost in fantasies of the girl next door. His sister, unaware, enters and catches him mid-act. Embarrassed, he quickly covers up, but the damage is done. She smirks, "You shouldn't do that, little brother." His cheeks flush red, but his cock twitches, betraying his arousal. He vows to keep his urges hidden, yet the thrill of near-discovery lingers.