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 mysterious space sage entrusts Yuma with challenges that surpass the limits of his imagination with a stake too high. He asks, "Should you fail… then you… will lose your power as Arc." The burden of protecting Hoshimoto City alongside SKIP members are twisted by Sascal, who manipulates them, sending challenge after challenge toward Yuma. Battling giant kaiju, an evil alien bent on destruction, and a warped dimension where even time itself is distorted, Yuma must confront the ultimate test. Will he... will Ultraman Arc overcome the greatest challenge yet and protect the future, surpassing the limits of the power of imagination?