Hiro is a super-genius whose father died when he was young. To partially replace him, he created Baymax, a robotic bodyguard. He was also a huge fan of Japan's greatest known hero, Sunfire. When Big Hero 6 (Japan's official super-team) began to form, Hiro was drafted. He refused initially but after an incident wherein his mother was held hostage and BH6 rescued her, he reconsidered and joined.