Rika, a mother who has raised her son Mamoru by herself. Recently, she seems to be in a romantic relationship with a colleague at her company, and Mamoru, the mother's father, is not happy about it. This feeling is so strong that before Mamoru knows it, he sneaks into her bed and has sex with her at night... One day, Rika decided to bring her lover to her house. Mamoru leaves the room, expressing his displeasure with her, but when he returns to the room, he finds Rika entangled with her lover! Shocked by her lewd appearance, Mamoru returns to Rika's bedroom to make her his own...