Rookie, a young Ultra from the Ultraman Kids franchise, attends class with Maa on Planet M7.8, a world shared by children of both Ultras and kaiju. In "Ultraman Kids Proverb Stories," he appears as a secondary character fostering a close friendship with Taa and actively supports Maa during bullying incidents involving Bal.

He reemerges in "Ultraman Kids: 30 Million Light-Years in Search of Mother," again as a secondary character. His consistently shy, timid, and soft-spoken personality surfaces during a collaborative spaceship project to locate Maa’s parents. Rookie contributes spontaneously by proposing "Kids Star" as the spacecraft’s name, an idea the group unanimously accepts.