Tatsuo Shiiba, having moved to Tokyo for school and started living alone, returns home as planned to oversee renovations of his mother Naru Shiiba's house. During this time, his cousin Masaru Saeki and Masaru's mother, Mako Saeki, come to live with them. Upon returning, Tatsuo becomes intensely sexually aroused by his relationship with his mother, and these feelings escalate into dominant fantasies, leading him to repeatedly engage in sexual acts with her—eventually culminating in creampie sex. Meanwhile, Masaru begins to see his aunt Mako as a woman, causing inner conflict that increasingly affects their daily lives. On top of witnessing Tatsuo's incestuous relationship with his mother, Masaru also becomes involved in his own taboo encounter with her. A story unfolds within the household, entangling complex interpersonal dynamics and raw sexual desires.