In the dim light of their shared bedroom, a curious sister can't help but notice her brother's growing bulge. As she watches him sleep, her mind wanders to forbidden thoughts, imaging the size and shape of his cock. When he wakes, she blushes, but he notices her gaze, leading to a heated argument. Later, she finds him jacking off in the bathroom, his cock even bigger than she imagined. Unable to resist, she joins him, their mutual masturbation escalating into an intense, taboo encounter.