Ultra Brothers, Eternal Vows (ウルトラ兄弟永延の誓い Urutora Kyoudai Eien no Chikai) is the 34th episode of Ultraman Leo. It features Gen Ohtori/Ultrman Leo teaming-up with Ultraman Jack, featuring the return of Jiro Dan as Ultraman Jack's human host, Hideki Go.
Because Dan can't transform into Seven after the battle with the Giras Brothers, Ultraman Jack flies to Earth to deliver a Monster Capsule and get his Ultra Eye fixed, but along the way he gets involved in a battle with Ashuran. He loses, and his human host Hideki Go's mouth was sealed by the Monsters during the battle. He crash lands on Earth where Gen finds him, but the monster capsule was left behind.
Jack was on his way to deliver a ball that would compensate for Dan's inability to transform, but he was attacked by the space monster Ashuran midway. He landed on Earth, but the injury was too much for his human host, Go, all while losing both his consciousness and the ball. Gen and a MAC officer brought him to the Jonan Sports Center for treatment by Momoko.
Not long after, Ashuran arrives and rampages on Earth. As the Jonan Sports Center was evacuated, Go took a nearby motorcycle to go to the same beach he landed on and managed to reclaim the ball from a group of stone-throwing children. Handing the ball to Dan, the disguised Ultraseven fling it and summon Sevenger into fighting the evil space monster. Unfortunately for them, Sevenger retreated after its fighting period ended despite being close to killing Ashuran. The monster nonetheless retreated at the sight of all three Ultras present in their human host/forms.
Dan exhausted his energies to free Go from his muzzle. At night, Ashuran prepares to attack MAC's Tokyo base. Since Ashuran is a space monster whose power is equal to two Ultras, Dan refrain Gen from fighting until Go recover from his injuries. Unfortunately the two were stubborn enough to join anyway while Jack uses the lunar eclipse to recharge his energy. With Ashuran defeated, Jack left the Earth with Dan's damaged Ultra Eye.
- Ultraman Leo Volume 9 features episodes 33-36
- Complete DVD-Box features all episodes
- During the sequence in which Jack travels through space while carrying Sevengar's capsule, a brief close up shot of Jack's hand has the suit actor's forearm visible.
- This episode was later featured in New Ultraman Retsuden episode 150 "Leo, Jack Coalition! Eternal Vows of the Ultra Brothers."
- Despite what the photo above suggests, Sevenger and Leo do not appear in the same scene.