Ryuuichi Kashima, a teenager, must adjust to his new life as the guardian of his younger brother Kotarou after losing both parents in a horrific aircraft disaster. Although Ryuuichi can retain a warm and kind manner, Kotarou is a quiet toddler who is still too young to comprehend the gravity of the situation. They are contacted during their parents' burial by Youko Morinomiya, the stern chairperson of an exceptional academy, who chooses to take them under her care. However, in exchange for a roof over their heads and enrollment in the school, Ryuuichi must satisfy one condition: he must become the school's babysitter. A babysitter's club was formed to assist the academy's female teachers in caring for their young children.