Battle! The Leo Brothers vs. the Ultra Brothers! (決闘! レオ兄弟対ウルトラ兄弟, Ketsu tou! Reo Kyoudai Tai Urutora KyoudaiUltraman Leo. It is the first part of a two-part arc which includes Gen Ohtori/Ultraman Leo and "Astra" fighting against the four Ultra Brothers, the Original Ultraman, Zoffy, Ultraman Jack and Ultraman Ace.) is the thirty-eighth episode of
The Ultra Key, an item of immense power, was stolen! Was Astra, Leo's brother, the villain behind this crime?
An unknown person steals the Ultra Key. The Ultra Brothers, Ultraman, Ultraman Jack, and Ultraman Ace, set out in pursuit, suspecting Alien Babarue to be the one behind it, but are confronted by Astra! Astra defeats Ultraman and flees.
The key's loss causes the M17 to go off orbit, setting it on a collision course for earth. This causes major interferences in MAC's systems, making communication impossible. With the systems down, MAC is unable to find out what the problem is, but on the blurry screens, Dan sees an Ultra Sign.
Dan takes Gen aside and tells him that the sign meant the Ultra Key has been stolen from the Ultra Planet, and that Astra is coming. Gen is excited at the news that his brother is approaching earth, but Dan tells him that Astra was the one who stole the key, and that the Ultra Brothers are pursuing him! For Leo to prove himself, he has to be the one to take the key from his brother.
Meanwhile, the MAC backup computer discovers the Ultra Planet is approaching earth fast. Soon, it begins to affect the earth's atmosphere, causing tsunamis, strong winds, and other abnormalities. Astra nears earth, and Dan is told there is no time: the key must be retrieved to prevent earth's doom.
Despite Gen's protests, Dan orders him to attack. Astra arrives. Then the Ultra Brothers arrive and attack him, with Dan using his ultra psychokinesis to restrain Astra. Astra, calling out "Leo-niisan," causes Gen's brotherly instincts to arise, and he attacks Dan! Eventually, he manages to knock Dan out, and transforms to attack the Ultra Brothers and defend Astra.
- Ultraman Leo Volume 10 features episodes 37-40, & Complete DVD-Box features all episodes