After losing both parents in a fatal plane crash, teenager Ryuuichi Kashima must adjust to his new life as the guardian of his younger brother Kotarou. Although Ryuuichi is able to maintain a friendly and kindhearted demeanor, Kotarou is a reserved toddler still too young to understand the reality of the situation. At their parents' funeral, they are approached by Youko Morinomiya, the stern chairman of an elite academy, who decides to take them under her care. However, there is one condition Ryuuichi must fulfill in exchange for a roof over their heads and enrolment in the school—he must become the school's babysitter. In an effort to support the female teachers at the academy, a babysitter's club was established to look after their infant children; unfortunately, the club is severely s