In the Otsuki household, the father, Yoshio, is assigned to a long-term overseas post, leaving the mother, Hibiki, and her two sons (Haruki and Yuma) to stay at home. As their father remains away, the eldest son, Haruki, vows to "protect his mother" and directs his strong feelings towards her, confessing his love for her for a month... The younger brother, Yuma, witnesses this and develops complicated feelings, eventually realizing his own feelings for his mother. The brothers clash with their respective feelings, compete for their mother's affection, reconcile, understand each other, and yearn for one another.