In a peculiar arrangement, the Kinomoto family, longing for a son, and the Yazaki family, yearning for a daughter, decide to exchange one child each for a three-month period. The protagonist, a boy from the Yazaki family, is thrust into the Kinomoto household, where his initial hurdle is earning the endearing title of 'Onii-chan' from all five sisters. With this unexpected twist, the protagonist embarks on a new chapter in his family life.