Reiko Kobayakawa once worked as a model before moving to a publishing company, building a life with her husband and family. However, when her father-in-law's dementia worsened, she quit her job to care for him full-time. Despite having retired, the father-in-law remains deeply attracted to Reiko's alluring, sensual figure. Pleased by her presence, he becomes increasingly aggressive—especially after seeing her in revealing swimwear—and begins forcefully molesting her, fueling his own escalating desire. Seemingly aware of his intentions, he intensifies his advances, overwhelming Reiko until she can no longer resist, her body responding with arousal, eventually allowing him to penetrate her. Taking advantage of her husband's absence, their forbidden relationship grows deeper, evolving into a relentless incestuous affair.