Yuri, who runs a snack bar, is the mother-in-law. Her son-in-law, Tetsuhei, has been captivated by Yuri's unique allure and sexy body from her night job. One day, while cleaning, Yuri hits her head and faints. Tetsuhei, who happens to see this, tries to take care of her but is drawn to her exposed breasts and plays a prank on her. Having tasted the forbidden fruit of his mother-in-law's body, Tetsuhei's desire accelerates, pushing further with Yuri, who is growing suspicious, saying, 'Let's check if that sperm is mine...!' The two find themselves trapped in an incestuous affair they can never reveal to their family...
