Sumire suffers daily from her husband's erectile dysfunction. Trying to distract herself through exercise, she one day discovers her son-in-law Shinya secretly masturbating while watching her. Overwhelmed by an intense urge upon catching sight of Shinya's huge cock, Sumire begins secretly helping him ejaculate day and night, under the pretense of relieving his pent-up desires. Exhausted by his stepmother's relentless, round-the-clock acts of service appearing at every moment, Shinya's mind gradually unravels, eventually spiraling out of control.