Natsuko lives with her husband and son, but both are always busy, leaving her feeling lonely day after day. To cope with her loneliness, she frequently masturbates. One day, her son accidentally catches her pleasuring herself in the kitchen. This incident sparks his growing curiosity toward his mother. One weekend, both her husband and son go out. After finishing housework, Natsuko lies down in the living room, exhausted, and falls asleep. That evening, her son returns home early from work. Seeing his sleeping mother, he becomes aroused by her back and buttocks, and can't resist pulling out his cock to jerk off. Natsuko senses something amiss and wakes up, sitting up in surprise—only to find her son visibly excited. Overwhelmed by the moment, he suddenly cums. Despite saying "I can only get excited by my own mother," Natsuko gives in and allows her son to have her body.