When Ryuuichi's parents pass away in a tragic plane crash, he takes on the responsibility of raising his quiet younger brother, Kotarou. Despite the immense emotional turmoil, Ryuuichi remains optimistic and dedicated, while Kotarou struggles to process their devastating loss. At the funeral, they meet Youko Morinomiya, a strict leader of a prestigious academy who offers them a place to stay. However, there is a catch: Ryuuichi must become the academy's babysitter. The school has created a child care team to support their female staff but is lacking in manpower. Ryuuichi must not only care for his brother but also manage a lively group of children, each with their own distinct personalities. While the opportunity seems rewarding, it quickly becomes a daunting challenge for Ryuuichi.