Miku Aoki and Sumire Shiratori are close friends who bond over their shared struggles as married women, confiding in each other about their sons and the emotional voids in their daily lives. One day, their usual conversation takes a turn toward romance and intimacy. Sumire shocks Miku by revealing she has had sex with her own son. Feeling neglected by her husband, Miku becomes both stunned and intrigued, eventually opening up to Sumire about her own desires. Curious and excited, Sumire agrees to help Miku explore her fantasies. A few days later, Miku and her family visit Sumire's home, where the two mothers cross a new boundary, embarking on an illicit, adult relationship that spirals into taboo pleasures involving their sons.