Kid Buu is Majin Buu's original form. Although he appears smaller and weaker than Super Buu, he is completely free of restraint, holding his own against Super Saiyan 3 Goku, Fat Buu, and Super Saiyan 2 Vegeta, and even Mr.Satan. When inside Super Buu, Goku and Vegeta ripped out Fat Buu, causing Super Buu to revert to this form. In this form he is extremely unpredictable, and thus extremely dangerous.
Destruction of Earth
Kid Buu also destroyed Earth for the first time. Kibito Kai used the Instantaneous Movement technique, bringing along Goku (who was already struggling to focus on Instant Transmission), Vegeta, Dende, and Hercule with him, which angered Vegeta because Goku didn't transport their children, Goten, Trunks and Gohan, or Piccolo to the Kai's Planet.
After Earth was destroyed, Kid Buu flew throughout the galaxy, blowing up planets, looking for Goku and Vegeta. Concerned by this, Goku and Vegeta raised their power levels so Kid Buu could detect them and find his way to Other World. At the Sacred World of the Kais, Kid Buu had arrived. Goku and Vegeta then did rock, paper, scissors to determine who will get to fight him first. Goku won and starts out the fight, transforming up to Super Saiyan 2 to start the fight, then later ascending to Super Saiyan 3 to fight Kid Buu. Goku put up a seemingly even fight with Kid Buu, although occasionally Vegeta cut in. After an extremely intense fight, Goku realizes that he let the fight stretch on too long. Goku, weary from the fight, reveals that he had let the fight drag on with Kid Buu, so Vegeta would have a chance to finish him. Goku asks Vegeta to distract Kid Buu for one minute, so he can bring his energy back up to a high enough level to finish him off. Goku tries to go to full power, but he can't because he is too tense to acquire the energy, as a Super Saiyan 3, and comes close to reaching his apex in power before his energy level starts descending again. Vegeta was no match for Kid Buu, before Kid Buu kills Vegeta, Hercule tries to fight him. Kid Buu, looking at Hercule tries to kill him but cannot due to Fat Majin Buu's memories about him. He suddenly spits out Fat Majin Buu. Now, purified of all influence, Kid Buu moves forward to kill Hercule, but is stopped by Fat Majin Buu and engages in combat with him.
The Spirit Bomb
Vegeta then talks to Dende, and the Kai's telling them to go to Namek and find the Dragon Balls. After they found it, Vegeta tells them 2 wishes, get Earth back, wish alive everyone who got killed by Majin Buu except the ones that are evil. Surprisingly, Vegeta was also alive again. Vegeta tells Goku to make a Spirit Bomb. Vegeta tells the inhabitants of Earth to lift up their hands to give their energy, they wouldn't listen so Goku tries to convince them, some people he knew from his childhood raised up their hand. The energy was still not enough and most people wouldn't listen, so Hercule tells them to. Everyone recognized "the world champion's" voice and lifted up their hands. Fat Majin Buu was almost killed by Kid Buu, so Vegeta stepped in and was crippled by Kid Buu. Goku could not throw the Spirit Bomb because Vegeta was in the way. Kid Buu notices this and steps on Vegeta, while on Vegeta, he keeps shooting Goku with his energy blasts. Fat Majin Buu punched Kid Buu out of the way and Hercule got Vegeta out of the way and Goku launched the Spirit Bomb. But Kid Buu was able to push it back and Goku didn't have enough energy to push it back. Vegeta just realized they had one more wish left, so Vegeta told Dende to wish Goku back to full power. Strength restored, Goku powered up to Super Saiyan to push back the Spirit Bomb to completely destroy Kid Buu.
Legacy and Uub
Ten years later, Gohan and Videl got married and had a daughter named Pan. That year Goku, Gohan, Goten, Vegeta, Trunks, Hercule, Majin Buu and Pan enter the World Tournament. Hercule told Fat Majin Buu to win every round, but lose to him on purpose in the finals. He said as a reward, one day Hercule would let Majin Buu beat him. There was also a young competitor named Uub who entered the tournament who was unknowingly Kid Buu reincarnated as a better person. Uub fought Goku but, Uub lost. Goku said that Uub was very strong, but he doesn't know how to control his powers so Goku stayed in Uub's village for some years, Pan got mad because Goku promised to spend more time with her.
- Kid Buu's only lines in the FUNimation dub of Dragon Ball Z are "Buu squish you like bugs", "Dumdums", "Peekabooboo", "Buu got you!", "Me Buu, kill you!", and his final words, "Me Buu, not you!", the last of which were spoken to the fat innocent Buu.
- Kid Buu is the only villain to be resurrected as a protagonist.
- In all 276 (or 291) episodes of Dragon Ball Z, Kid Buu is the only character to be killed by Goku (with the exception of Yakon, who ate too much of Goku's energy and exploded). In addition, Kid Buu was the only enemy in manga canon who the Spirit Bomb was effective against.
- Also, while Cell implied that he could use the Spirit Bomb from Goku's DNA, Kid Buu is the only villain that seems to also utilize it, as it was moving the Spirit Bomb and hurl it back at Goku.
- Kid Buu's disintegration in the Spirit Bomb resembles that of Super Perfect Cell in Gohan's Kamehameha. Both Buu and Cell had absorption, transformation, and regeneration abilities.
- Kid Buu is the only villain in the Dragon Ball Series who succeeds in blowing up the Earth.
- Kid Buu is the fastest form of Majin Buu in the Dragon Ball Z: Budokai Tenkaichi series.
- Kid Buu is the only villain in canon to actually die while in Other World. Android 17, who was killed during Semi-Perfect Cell's self-destruct on King Kai's Planet, doesn't count, as he never caused any destruction following Super Perfect Cell's death, and was revived by the wish made during the Kid Buu Saga that brought back everyone except for the evil ones.
- Kid Buu's voice tone changes slightly from high-pitched to a lower pitch after he expels the good Majin Buu.
- Kid Buu is the last character to die in Dragon Ball Z.