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.
In 1976, a drifting star named Gorath is discovered to be on a collision course with Earth. Although it is smaller than Earth, its enormous mass is enough to destroy the planet totally. A mission sent to observe Gorath is destroyed after the ship is drawn into the star, with a later mission barely escaping the same fate. However, Astronaut Tatsuma Kanai is left in a catatonic state due to his near death experience. Unable to destroy the invading star, Earth's scientists undertake a desperate plan to build giant rockets at the South Pole to move the planet out of Gorath's path before it is too late.
Shipwreck survivors found on the presumably uninhabited Infant Island leads to a scientific expedition that discovers a surviving native population along with the Shobijin, tiny twin fairy priestesses of the island's mythical deity called Mothra. After the fairies are kidnapped by an exploitative businessman named Clark Nelson, Mothra sets out to rescue them.
Nuclear tests create a radioactive man who can turn people into slime.