After a tragic plane crash claims his parents' lives, teenager Ryuuichi Kashima finds himself thrust into the role of guardian for his young brother Kotarou. While Ryuuichi remains compassionate and welcoming, Kotarou, still a small child, grapples with the harsh reality of their loss. The arrival of Youko Morinomiya, the strict head of a prestigious academy, offers them a new home and education but with a unique condition—Ryuuichi must oversee the school's childcare program. Tasked with aiding the female faculty by tending to their energetic toddlers, Ryuuichi not only cares for his brother but also a lively group of youngsters, each with their own spirited personalities.