20 years ago in Japan, the 4 Ultra brothers Ultraman, Seven, Jack, and Ace were fighting a deadly foe known as Yapool. The brothers were barely able to defeat Yapool but the monster still needed to be sealed. However, to seal Yapool away they were forced to give up the ability to transform, and took up jobs to be in the area of Kobe in case the monster ever returned.
20 years later Yapool is risen from the sea again by alien allied forces, and Mebius must fight the aliens and Yapool. But when Mebius is about to lose, the Ultra brothers come to aid Mebius in his battle against Yapool and the Aliens...
The setting of this movie takes place during the middle of the Mebius series. All members of Crew GUYS Japan are present in the movie, and Leo and 80 are not mentioned or shown. The actual placement of the movie in the order of the series is not explicitly given. The beginning of the movie's events is presumed to take place after the 80 series.
The series featured many firsts for the franchise, including the start of the story in a movie rather than the series proper. Ultraman Cosmos: The First Contact was the prequel to the series and took place ten years before episode 1. In it, 9-year-old Musashi Haruno encounters the being of light, Ultraman Cosmos, and befriends him as the two confront a threat to Earth.
Ten years later, Musashi, now 19 and a member of Team EYES, once again encounters the being of light from his childhood. The dark being Chaos Header has appeared and is corrupting the monsters of Earth, making them become ravenous and violent creatures that threaten humanity. Through Musashi's will to see the beasts and humans live in peace, Cosmos grants him a new power that will allow him to heal the corrupted creatures.
