An enjoys living with her adult daughter and son-in-law Koichi while the couple saves for a home. But her much older husband's sex drive has faded, leaving her to spend lonely days satisfying herself. When An secretly watches Koichi masturbate and sees his exceptionally huge cock, she becomes obsessed. Convincing herself that it will preserve harmony in both marriages and the family, she relentlessly seduces him day and night. Unable to resist his mother-in-law's lewd advances, Koichi climaxes again and again until he can no longer live without her.