Dr. Tetsu Segawa [Greg Joung Paik], a Chronos researcher, is on the run after stealing an alien device known as the Guyver unit. He is swiftly caught by Lisker [Michael Berryman], Chronos’ ruthless right-hand man, and his thugs. Lisker transforms into a Zoanoid and kills Segawa, who was also a Zoanoid, before returning the metal briefcase to Chronos’ president, Fulton Balcus [David Gale—link only to actor; if you prefer full name, use as shown], only to discover that it contains an old toaster because Segawa had hidden the unit in a pile of trash before capture. At a dojo, Max Reed informs Segawa’s daughter Mizuki Vivian Wu about the incident, while her boyfriend, Sean Barker, struggles to pay attention in class. Sean follows Reed and Mizuki to the crime scene; he stumbles upon the Guyver unit stored there and stuffs it in his backpack.
On his way home, his scooter breaks down in a back alley, and a gang corners him. The Guyver activates and fuses with him, transforming Sean into a newly armored fighter. He dispatches the assailants, though he is initially stunned by his own appearance, as the armor quickly dissolves into two scars on the back of his neck. The next night, Sean goes to Mizuki’s apartment and discovers his sensei murdered and Mizuki abducted by Lisker’s thugs. With Reed’s help, Sean rescues Mizuki, and the trio are chased by Lisker’s gang of Zoanoids. They are trapped in an abandoned warehouse, where Mizuki is held hostage and Sean once again transforms into the Guyver to battle them. Sean defeats the Zoanoids before facing Lisker himself. In a brutal sequence, a headbutt temporarily malfunctions the armor’s Control Metal, exposing a weakness that Lisker and his cohort exploit to try to strip Sean of the power. During the melee, Sean unintentionally kills Lisker’s girlfriend, Weber [Spice Williams-Crosby], but he wrongly believes Mizuki may also be dead. The Zoanoids close in; Lisker rips the Control Metal off Sean’s forehead, disintegrating the armor into liquid and killing him.
Mizuki wakes up at Chronos headquarters, where Balcus shows her a gallery of Zoanoids and questions how Sean could activate the Guyver. Dr. East [Jeffrey Combs], head of genetics research, discovers that the Control Metal is regenerating itself into a new Guyver unit. After Reed is subjected to experiments, Mizuki attacks Balcus and seizes the Control Metal, threatening to drop it into a disposal chamber. The Metal begins attaching itself to her hand, preventing its loss, until M.C. Striker [Jimmie Walker] inadvertently flings it off Mizuki’s hand, and it is accidentally swallowed by Dr. East. East begins to spasm and dies after being opened from the inside, and a newly revived Sean bursts through East’s body as the Guyver unit reanimates its host. Sean and Mizuki free Reed from the experimental chamber, and Sean once again battles Lisker, killing him and the other Zoanoids. Reed mutates into a cockroach-like Zoanoid, but dies when his system rejects the new form. Balcus proclaims that Sean must surrender the unit but cannot, as the Guyver is permanently bonded to him. Balcus reveals his true form as the Zoalord and corners Sean, but the Guyver’s defense system activates the Mega Smasher Cannon on his chest, obliterating Balcus and the laboratory. Sean deactivates the Guyver armor and departs Chronos HQ with Mizuki, as Reed’s former partner Col. Castle Castle and M.C. Striker look on.
