Five years after remarrying, Rin finds herself living a life of quiet emptiness. Her husband's son, Kakeru, is reclusive, and an uneasy stillness lingers throughout the house. One day, Kakeru accidentally catches sight of his stepmother's nipples in the bathroom, and overcome with desire, he lunges at Rin while she's cleaning, obsessively tormenting her sensitive nipples. Despite resisting, Rin's body begins to respond involuntarily, her resistance weakening as pleasure slowly takes hold. Immediately after sending her husband off, their illicit relationship begins—and gradually, Rin herself starts craving it. A dense, forbidden tale depicting quiet betrayal and dependency unfolding within the household, where downfall begins with the nipples. Each step into taboo pleasure is intricately portrayed, entwining deep-seated impulses and inner conflict as she sinks further into forbidden desire.