After divorcing, the mother raised her younger son while the older brother lived separately. Following the death of her ex-husband, the three planned to reunite for a trip. However, due to the younger brother's schedule, only the mother and her eldest son embark on the journey together. Over time, the son, who hasn't seen his mother in years, begins to see her as a woman and confesses his long-hidden feelings. Initially refusing, Chisato Shoda eventually gives in to his intense emotions—just once. But the overwhelming pleasure they share cannot be contained to a single encounter, and soon mother and son plunge into a forbidden relationship, beginning a new, illicit bond filled with obsessive desire.