Several years after visiting his brother's family home with his son, Masahide reunites with his niece Mahoro. Though he treated her affectionately as in the past, when they bathe together, he finds his eyes drawn to her changed appearance. Mahoro's body has developed far beyond what her age would suggest, possessing unusually large, mature breasts. Before long, Masahide becomes captivated by her physical transformation, and feelings toward her begin to shift into something entirely different.