|Date of birth||Age 774|
Uub is from the universe we are all familiar with, Universe 18. Majin Buu seems to be "trapped" inside the boy's body as Vegetto from Universe 16 put it, but in reality Uub is just the reincarnation of the evil Buu who once wreaked havoc on planet Earth. Gokū took young Uub under his wing and agreed to train him in order to make him stronger and to one day replace Gokū as the keeper of the peace in their universe. Uub has entered the tournament to show Gokū and his other friends how much stronger he has become.
Unlike his former incarnation, who was a maniacal being whose only goal was to cause destruction for his amusement, Uub was rather timid, polite and lacks self-confidence. However, after training with Gokū, he has a slightly more confident personality, though he still acts very respectful towards his elders. Unlike Pan, who believes that Martial Arts is like a game, Uub takes his training very seriously, hence making a lot of progress.
In the novel, Uub is revealed to have romantic feelings for Vegeta's daughter, Bra, with the feelings seeming to be mutual. Due to Uub's timidness, as well as fear of Vegeta's disapproval, the relationship does not progress.
After he was taken under Gokū's wing as his disciple, Gokū showed Uub and Pan the basics of fighting by battling with Vegeta as Super Saiyan 2's. Despite Gokū's confidence that Uub will surpass them, Uub is both confused and doubtful.
Years later, Uub's training has paid off, even mastering the Kaio-Ken that helps to multiply his power. Their training was cut off when they were invited to the Multiverse Tournament. Gokū, eager to battle as well as test Uub and Pan's skills, signs both of them up into the tournament. Uub has been seen with Gokū in nearly every panel. Mainly, since Gokū has been introducing Uub to everyone he fought in the past. Uub is worried on the large amount of villains, but Gokū reminds him that he has surpassed them(unknowingly about Cell's new power).
In the first round Uub was scheduled to fight against Tidar from Universe 19. Tidar challenges Uub with his many weapons of nanotechnology, first using missiles with homing devices in them. This is no trouble for Uub, and he is able to easily dodge all of them and blow them up at a safe range with ease.
However, when Tidar uses what he calls "God's Blade," he succeeds in cutting off Uub's arm. This infuriates Uub and results in Tidar being blown to ashes with a single energy blast. Babidi from Universe 11 offers to heal Uub's arm for a price, but Uub declines the offer. Majin Buu from Universe 4 then perfectly heals Uub's arm, saying that he feels close to Uub due to the fact that "he has a little bit of Buu in him."
Acting as a spectator in later rounds, Uub easily proceeded to the second round after his would-be-opponent, Nail, forfeited, leaving Uub to be matched up against Majin Buu from Universe 11.
Uub's next match is with Majin Buu of Universe 11. Uub charges a Kaioken, then attacks Majin Buu. Buu tries to absorb him, but fails, as Uub hits him with a ki attack. Uub then charges a Kamehameha, which turns Majin Buu into tiny selves of him. The tiny Buu's attack Uub, but Uub defeats them, and Buu turns back into one piece. Majin Buu attempts to turn Uub into cake, but Uub bounces back the attack, and turns Majin Buu into a watermelon. Gokū and Piccolo are in shock, as they did not know that Uub could manipulate magic. However, there is one tiny Buu left, and that Buu turns himself back into his true self. When Buu gets turned back, Uub asks Buu to play a game with him, in order to trick him. However, Buu realizes this, and gets angry. Majin Buu attacks Uub, and Uub uses the Galactic Donut, which is one of Gotenks' moves. Uub then uses his Maximum Kaioken, and charges a Super Kamehameha. One of Buu's mini selves is the only one left, Uub then uses a Mysterious Attack, in order to hide him, until the referees count the 30 seconds. Buu almost escapes. Babidi tries to use a spell in order to get Buu out of the attack, however Supreme Kai stops him from doing so, as it is against the Tournament rules. Majin Buu finally escapes, but it is too late, as it has already been 30 seconds. Uub of Universe 18 wins the match, and he shall move on to the Fourth Round.
Kaio-Ken: Uub has the ability to use Kaio-Ken, taught to him by his mentor. He can also use Kaio-Ken to the maximum.
Kamehameha: Uub can use Kamehameha, taught to him by his mentor.
Super Kamehameha: A more powerful version of the Kamehameha, taught to him by his mentor.
Magic Manipulation: Uub has the ability to manipulate magic, inherited from Buu. He first demonstrated this ability when he sent a Chocolate Beam that Majin Buu fired at him back at Buu.
Galactic Donut: Uub was first seen using Galactic Donut during his fight with Majin Buu of Universe 11. Since the original creator of this technique is Gotenks, he must use the trademark "TM" when he uses this attack.
- Gokū taught Uub how to use multiple levels of the Kaio-ken technique. This was confirmed in the official novelization of Dragon Ball Multiverse and art drawn by Gogeta Jr. (shown right).
- In the 30 years later minicomic he can go up to Kaio-Ken x40,000,000.
- Uub and Gast appear to be the only two characters in DBM that have no counterparts in any other Universe.
- However, an argument can be made that they both do, since Uub is the reincarnation of Buu, and Gast is made up of all Namekians alive during the Freeza Saga.
- There also is a possibility that Uub could have been born in Universe 20, but only if Broly went on his killing spree after the events of the Majin Buu Saga.