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.

A team of geophysicists investigating seismic activity on the seafloor discover that the islands of Japan, after suffering from massive volcanic eruptions and earthquakes, will be pulled into the ocean, killing millions.

1967 film by Kihachi Okamoto