"I don't want to see Mother looking lonely anymore," her grown son says gently, touching Mayu's heart—but his words only push her further. Suffering from a sexless marriage, she had let those words slip in front of her son, unknowingly igniting his actions. The moment they cross the taboo of incest, she is swallowed by a whirlpool of fear and pleasure. Abandoning reason, she chooses to surrender herself entirely to the emotions of this moment. That single, fleeting decision becomes a giant step for her.