Hotaru has been married for 30 years. Her only son, Kenji, has graduated from high school and is now a member of society. One night, Kenji finds Hotaru's pubic hair in the bathroom and becomes excited. He masturbates while fantasizing about his mother giving him a handjob and splashing his semen on her pubic hair. Meanwhile, Hotaru accidentally sees her son masturbating and the sight of his penis brings back a tingling sensation she had almost forgotten.