A remarried couple with each other's children—a total of three kids (two sisters close in age from the wife's side and a college-aged son from the husband's side)—are having breakfast together. The parents are going on a three-day trip to Atami starting from noon. That evening, when their son returns home and is relaxing, his youngest sister enters his room and starts pushing him... And from the next day, another sister joins in, beginning a 3P life with his stepsisters...
