Seiji Hokuto is Ultraman Ace's male human host. His female partner and former fellow host was Yuko Minami.

Seiji was a truck driver for an orphanage, and was delivering bread for the children when the first Terrible-Monster Verokron attacked Tokyo. Seiji bravely continued on his way back to the Orphanage to evacuate the children with his truck but the missile Terrible-Monster obstructed his truck off to the side of the road. Undaunted, Seiji continued to the Orphanage. After arriving he help a nurse, Yuko Minami, move all of the children to a save bunker. Both Seiji and Yuko return into the Orphanage building to rescue any remaining children, however Verokron's missiles brought the building down on the two brave humans, killing both of them. Ultraman Ace saw the heroic action of the pair from afar and gave to them his life and the Ultra Rings, so that the three of them would fight against the Terrible-Monster and their evil master, Yapool.