Azusa has been working as a housekeeper for over twenty years. In the household where she works, a pair of siblings live after losing their parents—older brother Kenji, a salaryman, and younger brother Mitsuru, a reclusive ronin student. One day, Mitsuru discovers a shocking secret: Azusa was actually the woman who took his older brother Kenji's virginity. As the truth comes to light, the brothers' relationship, the household atmosphere, and Azusa's position within the family begin to shift in unexpected and intense ways.