One day, a strange creature appeared in the waters near Okinawa. Its appearance resembled that of a crown-of-thorns starfish, and its venom harmed fishermen while rapidly spreading across Japan. This signaled the resurrection of the monster Dagahra, created by the legendary ancient civilization Nirai Kanai as a biological purification system to solve environmental pollution, but it had gone out of control, ultimately leading to the downfall of Nirai Kanai. The Elias sisters sensed the impending crisis on Earth and flew to Ishigaki Island, where a small creature named Gogo, from Nirai Kanai, appeared. Poachers on the continent learned of treasures from the decorative rings on Gogo's tail, and some local girls took Gogo in. The Elias sisters knew of the legend that 'a treasure hidden in the ruins of Nirai Kanai could defeat Dagahra.' The girls, the Elias sisters, and the poacher and dark fairy Belbela, who had conflicts with the sisters, formed a team to go out to sea. Guided by Gogo, the pyramid ruins of Nirai Kanai emerged from the ocean. However, as they searched for the treasure, Dagahra descended upon Ishigaki Island and began wreaking havoc, prompting the Elias sisters to summon Mothra to fight it. Dagahra and Mothra engaged in a battle from Ishigaki Island to Iriomote Island, and then fought underwater near the pyramid ruins. Dagahra dragged Mothra, who excelled in sea combat, down into the ocean. Dagahra then attached 'its' countless Belons to Mothra, rendering her unable to fight. The Elias sisters desperately tried to remove the Belons clinging to Mothra, but there were just too many to eliminate. Mothra found herself in a dire situation; finding the treasure had become urgent. After escaping traps within the ruins, the girls and the poachers reached a hall where a 3D image of the princess of Nirai Kanai revealed that Gogo had chosen girl Shiori as the treasure's master. However, Dagahra attacked the pyramid! After the pyramid collapsed, Mothra was able to use the power of Gogo's 'Life Water' to remove the Belons attached to her, transforming into Rainbow Mothra, now even more powerful, and battled Dagahra once again. The situation was now completely different; Mothra held the upper hand. When Dagahra dived into the sea again, Mothra became Water Mothra, and the battle shifted underwater. Mothra defended against Dagahra's attacks with a barrier and launched powerful assaults on Dagahra. Later, she transformed into a doppelganger form and attacked from within Dagahra, defeating the Belons along the way, which ultimately caused Dagahra to fall, disappearing along with the pyramid. After Mothra emerged from the ocean surface, she reverted to her original form—Rainbow Mothra—and returned to Infant Island, bringing the crisis to an end.
