Futaba Mihara debuts in Episode 01 of the first season and reappears in Episode 33 of the second season. She serves as an operator at the Shinkansen Ultra Evolution Institute's Ōmiya Branch, coordinating field operations and providing mission support to Shinkalion pilots. Her surname originates from a station on the Sanyo Shinkansen Line, while her given name references a discontinued semi-express service on the Sanyo Main Line.

Flashbacks depict Futaba's childhood, establishing her early connection to the railway organization and tracing her development into a dedicated staff member. When Ōmiya Branch Director Hokuto Hayasugi transfers to Kyoto, Futaba steps into the role of acting director, signaling her growing responsibility. Her leadership is formally recognized in Episode 65 with her official promotion to director of the Ōmiya Branch, cementing her authority over its operations and personnel.

Episodes 68 and 69 offer glimpses into Futaba's personal life, introducing her apartment. Her duties extend beyond operations to include mentoring and overseeing the child pilots, especially during critical threats. The character maintains this consistent presence and portrayal across the series and other official media.