Yukari, tormented by unfulfilled desires, one day gets her hands on her son Wataru's yogurt. Drawn in by its scent and texture, she begins pleasuring herself with it. When Wataru discovers what she's been doing, he confronts her in the bathroom, furious and trembling with rage. But upon seeing his mother standing naked, her body and crotch smeared with yogurt, he is overwhelmed by uncontrollable urges and crosses the forbidden line.