Tsubaki began living with her daughter and son-in-law after her husband was transferred to a distant assignment. One night, she accidentally witnessed her son-in-law Takeshi masturbating, captivated by the sheer size of his massive cock. Sex-starved and blaming herself for her daughter's failed intimacy, Tsubaki becomes obsessed, relentlessly seducing Takeshi day and night. Unable to resist, Takeshi eventually gives in, surrendering to Tsubaki's sultry, aggressive advances despite knowing she is his stepmother.