Masaki was a free-lance journalist captured by Cronos and used as an experimental guinea pig in the Zoalord development program. He is a prototype body for the Zoalord form of Richard Guyot. Dr. Yamamura, a scientist involved in the project, discovered Guyot's plans for the Guyver units, and recruited four of the prototypes—including his old pupil, Murakami, in an attempt to destroy the Commander while he was being processed into his new battle form. The other eleven members of the Cronos Council of twelve—all Zoalords—intervened; Masaki is the only surviving rebel. He joins with Shou to fight Cronos, having his own revenge in mind. He doesn't quite trust Agito at first because of Guyver III's earlier connections with Cronos.