Goku and Uub. Close friends, student and mentor, and sparring partners. The story was like this, durring the final battle against Majin Buu, Goku asked if he come back as a good guy. King Yemma granted this request in the form of Uub, a dark-skin boy with a mohawk born in a village not far away from West City. This so happened to be the same village Nam (the one Goku fought in the World Martial Arts Tournament as a kid) was from.
Ten years after the Spirit Bomb Triumphant over the once devious Majin Buu (Kid Buu form), Goku, Vegeta and the rest of the Z-Fighters are at the World Martial Arts Tournament, Goku, Vegeta, Goten, Trunks, Pan, and Good Buu/Mr.Buu as competitors, Krillin, Marron, #18, Piccolo, Chi-Chi, Bulma, Turtle, and Master Roshi as spectators. Of course the Z-Fighters get past the preliminaries along with Hercule. Goku then asked Good Buu to use his magic to match him up with Uub. Goku then explains to Vegeta that Uub is the final form (technically first form, Kid Buu) of Majin Buu reincarnated.
So, when the match comes, it is revealed that Uub is the strongest in his village, but does not know how to fight. Goku then taunts him to get him mad, and Uub learns how to fight during this process. Afterwards, they leave the fight, Uub on Goku's back while Goku flies toward his village as he promised to train him.
Now, The New StoryEdit
It has been five years. No one has heard from Goku since he left to train Uub.
"I miss dad," said Goten, who was now twenty-two.
Gohan came from behind him and patted him on the back.
"Don't worry, he'll come back.