Hiroya Munakata is the leader of the yakuza group Munakata-gumi. After 10 years since the big fight, Hiroya Munakata's non blood-related younger brother Takashi is released from prison, but Takashi’s daughter, Hyuga says she does not want to meet her father and runs away from home. Hiroya, Takashi and Hiroya’s subordinate Shinya go to Zeni Island where Hyuga is headed to. Something they never expected is waiting for them.

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.