
Inventor Goro Ibuki creates a humanoid robot named Jet Jaguar. It is soon seized by an undersea race of people called the Seatopians. Using Jet Jaguar as a guide, the Seatopians send Megalon as vengeance for the nuclear tests that have devastated their society.

as Inventor Goro Ibuki

as Hiroshi Jinkawa

as Rokuro 'Roku-chan' Ibuki

as Japan Special Defense Forces Chief

as Lead Seatopian Agent

as Seatopian Agent

as Truck Driver's Assistant

as Man from Unit 1

as Emperor Antonio of Seatopia

as Truck Driver

as Antonio's Aide (Radio Operator in White)

as Godzilla

as Megalon

as Jet Jaguar

as Jet Jaguar

as Gigan (as Kengo Nakayama)

as Emperor Atonio of Seatopia (voice)

as Narrator

as Godzilla (archive footage) (uncredited)