One day, while Reiko is doing housework, her son Noboru suddenly approaches and starts touching her ass. He confesses, "I can't think of anything but you, Mom!" and forcefully embraces her, kissing her passionately. Overwhelmed by shock and pleasure, Reiko surrenders to Noboru and climaxes right then and there. From that moment on, whenever her husband is away, the two give in to their desires and indulge in an incestuous affair.