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.

Mothra's dark counterpart, Battra, emerges to eliminate humanity on behalf of the Earth. Two tiny fairies called the Cosmos offer their help by calling Mothra to battle the creature. Unfortunately a meteorite has awoken a hibernating Godzilla as a three way battle for the Earth begins.