UnlikeHiro Hamada is a young prodigy living in the high-tech city of San Fransokyo along with his aunt Cass and older brother Tadashi, who wants Hiro to become a productive member of society.
Despite his high intelligence, Hiro spends his time participating in underground bot fights throughout the city, which has frequently led to Tadashi having to bail him out of tough situations. On one particular night, Hiro takes part in an illegal bot fight against champion Mr. Yama and leaves the battle victorious. Out of spite, Yama and his goons attack the boy, who is immediately rescued by Tadashi. Though they escape Yama and his thugs, the two brothers, along with everyone else involved in the illegal bot fights, are caught by the police and arrested. Hiro and Tadashi are released that same night on account of Cass, who takes them home, scolding them along the way. The two are able to bypass punishment, but a frustrated Tadashi scolds Hiro on his bot-fighting obsession, wanting him to put his intelligence to better use.