The boy's eyes gleam with a mix of shame and excitement as he steals a pair of his sister's panties, the cute, white cotton briefs still warm from her body. He presses them to his face, inhaling her sweet scent, feeling the fabric's softness against his skin. His cock hardens, tenting his pants, and he can't resist the urge to free it. He strokes himself, fantasizing about his sister, about how her panties would feel against his cock. As he reaches the brink, he strokes faster, grunting as he spills his load onto the innocent garment, marking it with his forbidden lust.