After marrying Takeshi, Shihou begins living with her husband and his father, Mitsuru, forming a new family of three. Mitsuru is surprised yet warmly welcoming as the first woman to enter their previously all-male household. One day, Shihou accidentally breaks her glasses—essential due to her severe myopia—leaving her vision blurred and distorted. Drawn by strange noises coming from somewhere in the house, she heads toward the bathroom. Believing her husband is inside bathing, she unconsciously starts undressing. However, it is not her husband but her father-in-law Mitsuru who is present. Though shocked by the sudden encounter, Mitsuru begins secretly impersonating her husband, gradually seducing Shihou and manipulating her body. What begins as an accidental incident evolves into a forbidden, intimate relationship.