A nameless ronin, or samurai with no master, enters a small village in feudal Japan where two rival businessmen are struggling for control of the local gambling trade. Taking the name Sanjuro Kuwabatake, the ronin convinces both silk merchant Tazaemon and sake merchant Tokuemon to hire him as a personal bodyguard, then artfully sets in motion a full-scale gang war between the two ambitious and unscrupulous men.
A submarine expedition to salvage the remains of Mechagodzilla is thwarted by a massive dinosaur named Titanosaurus. An Interpol investigation leads biologist Ichinose to uncover the work of Dr. Mafune and his mysterious daughter Katsura. Aligned with the Black Hole Aliens, Katsura's life becomes entwined with the resurrected machine.
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.
