A joint expedition by Japanese and Rolisican scientists arrived on Infant Island to observe the effects of a recent Rolisican nuclear test. There, the expedition encountered the Shobijin and a tribe of natives who worshipped a goddess named Mothra. Clark Nelson, a greedy Rolisican businessman that was part of the expedition, kidnapped the Shobijin from the island and slaughtered several of the natives before bringing them back to Tokyo. The surviving natives on the island called upon Mothra, who hatched from her egg and went to Japan to rescue the Shobijin. After Mothra and the Shobijin were reunited, they returned home to Infant Island to restore peace and happiness.
Infant Island was the site of various nuclear tests, which devastated the island and reduced it to a nightmarish barren landscape. The only remaining green part of the island was a small sacred spring located in the interior of the island just outside a cave. Two reporters and a scientist from Japan traveled to the island to ask Mothra to stop Godzilla, but the bitter islanders angrily refused. The Shobijin sympathized with the Japanese people's plight, but could not bring themselves to call upon Mothra to fight Godzilla. Ultimately, Mothra herself decided to help the Japanese and fight Godzilla. Though Mothra was ultimately killed, her larvae hatched and defeated Godzilla, then returned to Infant Island.
One of Mothra's larvae died sometime after the battle with Godzilla, but one survived and took her mother's place as guardian of Infant Island. When King Ghidorah arrived on Earth and threatened to destroy the world, Mothra left Infant Island for Japan, where she convinced Godzilla and Rodan to join forces with her and send King Ghidorah back to space. Mothra then returned to Infant Island with the Shobijin.
A few years after the nuclear tests that ravaged Infant Island, the island began to recover and return to its lush green beauty. However, a terrorist organization called the Red Bamboo repeatedly raided the island and captured the natives, enslaving them and forcing them to make nuclear weapons and a special juice to hold off the monster Ebirah on Devil's Island. Yata, a shipwreck survivor, found his way onto the island and lived among the remaining Infant Islanders for a few months. When Yata's brother Ryota arrived to rescue him, the two decided to help the Infant Islanders and stop the Red Bamboo by awaken Mothra from her long sleep. The two men returned to Devil's Island and broke the slaves free, while Godzilla defeated Ebirah and destroyed the Red Bamboo. They then built a net and stood inside of it, when Mothra arrived and carried the net back to Infant Island before the island self-destructed.
Infant Island, located in Indonesia, was the refuge of Mothra and the Cosmos for thousands of years following Mothra's battle with Battra in the ancient past. An investigative expedition from Japan traveled to the island and encountered the Cosmos, as well as Mothra's egg. The Marutomo Company sent a boat to bring Mothra's egg back to Japan.