Nonton Godzilla vs. Megalon aka Gojira tai Megaro. The underground kingdom of Seatopia sends out Megalon, a giant beetle, and Gigan to destroy the above ground dwellers. In an attempt to stop them, an independently thinking robot brings Godzilla into the fight.
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.