Since childhood, Konatsu has harbored feelings for her older brother. One day, while their parents are away on a trip, she accidentally catches him masturbating as he moans, "Onii-chan..." When he discovers her watching, instead of running away, Konatsu boldly offers her large, mature breasts for him to touch and whispers, "You can do whatever you want with me, Onii-chan?" Unable to resist the innocent yet seductive advances of his adorable little sister, the brother gives in to her temptation.