Walnut moves into the apartment where Kiyohiko, an unemployed man in his 40s, lives. She has a cute appearance but large breasts, and one day, while out with her husband, she is approached by a man. Kiyohiko saves her from a difficult situation, leaving her unreliable husband behind. Walnut looks on with gratitude and envy. From the next day, Walnut appears without a bra under her clothes, and gradually seduces Kiyohiko.