The film follows Maruko, a cheerful little girl who returns to school at the start of the new term, where she is placed in a group with her friends Uno and Sugiyama. As the school Sports Day approaches, the rivalry between Uno and Sugiyama begins to intensify, turning into a conflict that threatens their friendship. Maruko steps in as a mediator, and through the experience, she and her friends learn profound lessons about the meaning of friendship, loyalty, and finding balance between competition and affection.