Momoko, a student at a specialized school, faces challenges due to her mental and physical disabilities, and longs to attend a regular school like her twin brother Riki. Her disappointment shows with grumpiness each morning, but her family soothes her with her favorite tune, "The Song of Frogs." At an open classroom day where Riki plays dodgeball, Momoko cheers him on and helps his team win. But when Ryuji from the losing team insults Momoko as Riki's "idiot sister," Riki hits him hard in anger. The next year, an inclusive education trial allows Momoko to attend Riki's school, but her physical health declines and she is hospitalized. Determined to lift her spirits, Riki and their classmates aim to win a relay race and share the victory with her. Yet obstacles arise as Ryuichi, the fastest sprinter, refuses to participate.