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.

In the beginning of the movie, 20 years ago, on the moon, the 4 Ultra brothers, Ultraman, Seven, Jack, and Ace were fighting a deadly foe known as Yapool, a monster that was several times their size. As they fought, Yapool had a clear advantage and used his several claws to grasp the brothers, although, they managed to clear from the claws through there powers and used a combined Specium Ray to no avail. The monster then flies off to Earth to dodge the attack and the brothers follow. 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.