Originally, this household was meant to be home to three people: the husband, the mother, and their son Shinsuke. However, due to disagreements over how to raise their son, the husband and mother separated, and the father moved out to live in a separate apartment. The mother had raised her son in an overly protective manner, which ultimately drove the father away. In the midst of this strained situation, the mother discovers her son engaging in masturbation. This incident triggers a new shift in their family dynamics.