Worried about his stepsister's new life while she's living alone in Tokyo, the older brother visits the city to check on her living conditions. However, the brother secretly harbors incestuous desires toward his stepsister. While investigating her room, which remains unpacked, he discovers a vibrator hidden beneath her futon. When he snoops around during her absence, he finds explicit videos of her with a man on her phone. Shocked by her irregular lifestyle, one revelation after another unfolds. ◆ Using the erotic videos as leverage, he joins her for a bath and indulges in her now fully developed breasts while she isn't looking. ◆ Sharing a tight futon, he presses his erect cock against her. Then, to his surprise, she starts touching it...!?