Momoko remarried later in life, becoming stepmother to her husband's adult university-student son, Takashi. Even after three years, they remain distant and overly formal. When repeated packages for Takashi make her curious, she opens one while he is out and discovers a revealing swimsuit. She calls it shameless, but temptation gets the better of her and she puts the tiny bikini on herself, setting an intimate adult stepmother-and-stepson role-play in motion.