Three years after visiting Mika's home, Masashi is thrilled by his sister Mika's beauty upon seeing her again. However, he witnesses an unexpected sight—his mother, Hisae, intimately entwined with Mika. Shocked, Masashi confronts Hisae the next day, and she calmly reveals their plan: "When this happened, we decided to all enjoy it together." With secrets no longer hidden, the truth is now out in the open between the mothers and son. Joined by Mika's son, the two families plunge into an intense close-kin incest orgy, where mother and child relationships blur in a tangled web of desire.