Every day, I bathed my mother in an atmosphere of pleasure. A month later, I repeatedly engaged in fertile sexual intercourse with my mother, whose rationality had collapsed. (Otsuki Hibiki, DASS-900)

In the Otsuki family home, the father, Yoshio, is stationed overseas for an extended period... The mother, Hibiki, and their two sons (Haruki and Yuma) remain at home. With their father absent, the eldest son, Haruki, vows to "protect their mother," harboring strong feelings for her and expressing his "love" for her for a month... Meanwhile, the younger brother, Yuma, witnessing this situation, experiences complex emotions and gradually realizes his own feelings for their mother. The two brothers exchange their thoughts, strive to win back their mother, and ultimately reconcile, understand each other, and become mutually dependent.