Ultraman Saga opens with a powerful apocalyptic vision of Tokyo, buildings destroyed and the city seemingly devoid of life. We are soon introduced to the Earth Defense Force (EDF), Team U (played by members of the female idol group AKB48). They and a group of young children and the last survivors on planet Earth after the world was invaded by the evil Alien Bat, the rest of the human population having been abducted.
A group of teenagers unleash a curse when they use haunted public lockers in Shibuya. Supposedly, if you leave a gift in one of the lockers you will be lucky in love. However, the results are anything but lucky as a creepy female ghost with long black hair soon shows up to kill them off one by one.
Once again, Musashi has encounter Ultraman Cosmos. Now Ultraman Cosmos has gained some new modes to defeat Scropis. Musashi has joined Team Sea to save the Blue Area. But there is mysterious evil monster, Sandros, who wants to destroy the Earth. Now it is up Musashi and Ultraman Cosmos to defeat Sandros and who’s the other Ultraman?
When he returns to Earth to attend the wedding of his friend in Saipan, Musashi meets a beautiful girl named Shau who claims to come from the bottom of the sea. Just then, Monster Scorpis reappears in the sky above the island and Musashi faces the monster in order to protect the girl. What is the girl's true form? And what is the strange shadowy form that follows the monster Scorpis?