One day, Masahiko was caught by his mother, Ichika, sniffing her used underwear. Panicking, he tried to flee but fell down the stairs and was hospitalized. While caring for him, Ichika—already emotionally vulnerable due to her husband's long-term work assignment away from home—found herself intensely drawn to her son's mature physique. From that moment on, their mother-son relationship took a shocking and irreversible turn.