Ultraman Leo is an Ultra foreign to the Land of Light, instead hailing from the fallen Planet L77 of the Leo constellation, where he and his brother Astra were royalty. After his planet was destroyed by Alien Magma and his twin Giras kaiju, Leo traveled to Earth, intending to make it a second home. While there, he blended into human society as Gen Ohtori, and became a gym instructor at a fitness club for children. But, when the Alien Magma that destroyed L77 came to conquer Earth, he was forced to take action. Leo met Ultraseven during his initial fight against Alien Magma, and became the first Ultra Crusader of Earth to not hail from the Land of Light. Unlike most of the previous Ultras to visit Earth, Leo's fighting style specializes in martial arts giving him far greater physical abilities than any other known Ultras. Despite his foreign origins, he, along with Astra, were readily accepted into the pantheon of the Ultra Brothers. During his tenure on Earth, Leo and Seven became very close, and it was for this reason that Seven would eventually entrust the training of his son Ultraman Zero to Leo and Astra.

Yapool, an ancient interdimensional race of beings tries to conquer the Planet Earth with his army of monsters, called Terrible-Monsters. The newest member of the Ultra Brothers, Ultraman Ace, arrives on Earth to aid humanity in the battle against Yapool. Touched by the sacrifices of Seiji Hokuto and Yuko Minami, he revives them and grants them the Ultra Rings, which allows them to transform into Ultraman Ace in times of need.

Josh Gates sets off on the most extraordinary expedition of his career. He'll journey over 50,000 miles to four continents to tackle mankind's greatest question: Are we alone in the universe?