Lonely on a quiet night, a sister longs to be fulfilled—until a lustful system appears and offers to send her back ten years. She wakes to a more alluring body, and the system issues its tasks: masturbate in front of her brother, with extra rewards for oral. She rides her bike pressed deliberately close to him, "accidentally" brushes against his already-hard reaction at a red light, and spends the whole day plotting how to complete tonight's mission.