Uubu is the Human reincarnation of Evil Buu, he grows to adolescense in the ten year calm after Evil Buu's destruction. Uubu enters the first World Martial Arts Tournament in ten years, in order to take home the multimillion zeni prize, to feed his village. However, Uubu is unaware that Goku has been waiting to fight him his whole life, yet Uubu had never met Goku in this life. Goku then has Majin Buu rig the Tournament's random selection system so that Uubu and Goku are the first fighters to combat.
Uubu enters the ring with Goku unsure of his abilities, but with fierce determination to help his village. As the fight is declared Goku begins to taunt Uubu in order draw out Uubu's incredible potential power level. Goku remains at a comfortable level as Uubu draws out his first burst of power, lunging forward with a powerful melee attack. The strength of the attack caught Goku off-guard and the battle commenced. With each blow Uubu's strength and skill increases, in essence learning to fight while doing so. An incredible feat for any race.
After some intense sparring, Uubu is almost knocked out of the arena, but clings to the edge desperately. Goku, still trying to draw out Uubu's potential, flies up into the air and prepares a Kamehameha Wave. However, as he is about to fire, the concrete that Uubu was clinging to crumbles and he is about to fall before Goku swoops down and catches his arm. Goku then notices that Uubu has not had a master to train him to fly or fight, so Goku offers to live with him in his village and train him.
Uubu is hesitant in accepting the offer because he needs the prize money in order to feed his village back home. Goku tells him not to worry, as his good friend Hercule has plenty of money and would be willing to help them out. Uubu is overjoyed with the new arrangement and after Goku says goodbye to h is family and friends, they set off towards his village to begin his training.
On their way to the village Goku stops and asks Uubu if they could fight once the training is complete. Uubu accepts, and Goku becomes so excited that tears well up in his eyes and he declares that he can't wait for that time to come. This is the last episode of Dragon Ball Z, and the next series Dragon Ball GT picks up where it left off, ten years later with Uubu's promised fight.