The Alien Alliance are the ones who are scheming to release Yapool from his imprisonment, but with Ultraman Mebius as an obstacle to their plans, the Aliens instead plan for a way to get rid of the Ultra, to which Alien Temperor aggressively declares that he will kill Mebius himself and rule over the alliance, to which the others calmly agree to. Inside the ship are a group for four aliens known as ' The Alien Alliance,' which consists of the Aliens: Alien Temperor, Alien Zarab, Alien Guts, and Alien Nackle. Suddenly while Mirai and Aya are together, Mirai (and the other former Ultramen) notice an Ultra Sign appearing in the Sky! According to the Sign (sent by Zoffy,) someone is attempting to release Yapool! At the same time, an Invisible Ship appears in Kobe and noties the same spot in which Yapool is sealed away in.

During their time together, Mirai also meets Aya's skittish little brother, Takato, but is unable to properly meet him as he is too shy, and runs off. Sakomizu) and has agreed to assist Mirai in his Investigation. There he meets a woman named ' Aya Jinguji,' who is an Oceanographer who is affiliated with GUYS (particularly with Capt. Now in the Present Day, the four former Ultras, now under their Human Forms have all lived their lives happily among Humans doing jobs that they particular enjoy ( Shin Hayata is an Airport Manager, Dan Moroboshi has become a Farmer, Hideki Goh is a Go-Kart Racing Manager, and Seiji Hokuto is a Baker.) Meanwhile, Mirai has arrived at Kobe to investigate the ocean nearby (the same location in which Yapool and U-Killersaurus were sealed away) as per a mission assigned to him by GUYS. Six months later, the newest member of the Ultra Brothers, Ultraman Mebius (under the disguise of ' Hibino Mirai,' and having joined the Earth's Defense Group: GUYS) recounts the previous events as being the final battle in which the four Ultra Brothers ever engaged in, as well as it being his inspiration to joining the Ultra Brothers in protecting Earth.

After some initial hesitation, the Ultra Brothers agree to do so with faith that the Humans will protect themselves from now on, and Yapool is sealed deep within Kobe Bay, never to return again. To ensure that Yapool never escapes though, the Ultra Brothers agree to seal away the entity for good by use of a technique known as the ' Final Cross Shield,' a technique powerful enough to keep Yapool imprisoned for eternity, but at the cost of their ability to transform back into Ultramen ever again. Defeated, an astral form of Yapool appears before the Ultra Brothers and vows that he shall recover to continue his reign of terror. However, the Super Beast is weakened and dismembered by both Ultraman and Ultraseven, while Jack and Ace manage to strike the Super Beast directly with their Specium and Metallium Rays, which greatly weakens U-Killersaurus and knocks the Super Beast into the Ocean off the shore of Kobe, Japan. U-Killersaurus tries to take advantage of the Ultra Brothers brief moment of weakness to ambush them with his tentacles. While fighting with the Ultra Brothers, U-Killersaurus flees from the Moon and attempts to take their battle with him to Earth, where countless lives could potentially be lost.

The scene opens up with the four Ultramen: Ultraman, Ultraseven, Ultraman Jack, and Ultraman Ace, all on the Moon and fiercely engaged in battle against U-Killersaurus, an extremely powerful Super Beast created (and controlled) by all of the collective hatred of Yapool. Can the Ultraman Brothers regain their powers to help Moebius fight the aliens? Will they succeed in their plans to revive U-Killer Saurus? When the aliens launch their combined attack, even Ultraman Mebius cannot defeat them. But the most powerful aliens that have ever battled the Ultraman Brothers have plans to release U-Killer Saurus and conquer the world. In the present day, Ultraman Mebius protects the Earth. They will spend the rest of their lives as ordinary human beings. But in doing so the heroes lose their super powers. The four Ultraman Brothers trap the beast under the sea. Four of the Ultraman Brothers - Ultraman, Ultra Seven, Ultraman Ace and Ultraman Jack - battle U-Killer Saurus, a monster is so powerful it threatens to overwhelm even their combined might!

Film ultraman mebius