The dreaded Yapool has come to Earth with his experiments, the "Terrible-Monsters" to take a first step towards his "inevitable" goal of galactic domination. Though the Ultras have vowed to defend our world from these attacks, it is a new figure that bears the brunt of that responsibility - Ultraman Ace. Divided between his two human hosts' personalities, Ace must learn to balance them both and his superior energy powers if he is to save the universe from this terrible new foe.