The Buu Saga starts out with the Tenkachi Bodoukai, and Goku being resurrected for only one day so that he can fight. Soon Doubler, the prince of darkness, turns Krillin and Piccolo to stone on the mountainside. Gohan, Goku, Vegeta and Ka-oo-shin travel into Babidee's space ship looking for this new menace. Babidee is trying to gather enough energy to resurrect Majin Buu, so he makes a game out of the warriors. He sends a warrior out to fight the heroes one at a time on each floor. Vegeta begins the game by devastating Babidee's first low class fighter. Goku takes on the second and wins overwhelmingly. But when it comes to the third fight, Gohan does not have such an easy time with the Prince of Darkness, Doubler. Doubler leaves half way through the battle saying that it was because he found another warrior for this 3rd out of the 5 stages of the ship. Babidee uses his magic to charm Vegeta, creating a new enemy for Goku -- Majin Vegeta!
Majin Vegeta and the Heroes get sent to the Martial Arts arena. After Majin Vegeta kills a few hundred people, Goku finally agrees to fight him. Disobeying Kai-oo-shin, Goku requests Babidee send them somewhere uninhabited. Vegeta finally admits to Goku that he allowed himself to be charmed so that he could finally battle Goku.
The titanic battle takes place, and the energy released from the battle is enough for Babidee to awaken Fat Buu. The two go flying around Earth, spreading mayhem and despair wherever they go. Majin Vegeta knocks out Goku but realizes that Good will always triumph in the end. He sees how useless his evil ways have been, and Vegeta finally becomes truly good. Majin Vegeta finds Buu and self destructs hoping that his sacrifice will destroy Buu. Unfortunately it is not enough and Buu survives.
Goku finally steps up to bat against Fat Buu, but cannot beat him. His rage sends him into SSJ3 for the first time. About this time Bulma begins gathering the dragon balls to wish back all those killed by the Majins. Buu gets angry at being Babidee's slave, so he turns on Babidee and kills him. Fat Buu, in an attempt to purify himself, splits into a Good Buu and an Evil Buu. The two battle and the Evil Buu wins, resulting in a trimmed down, more muscular version of Fat Buu.
Gohan travels to Kai-oo-shin's planet to train. He dons a native suit and begins using the Z sword. He learns how to use his hidden power without requiring the rage that it takes to go SSJ. Everyone else goes to Kame's Lookout, where Goku teaches Goten and Trunks how to fuse to become Gotenks. Goku then teleports to Kai-oo-shin's planet to watch everything from there. Buu senses this huge power and travels to Kame's Lookout to search out this huge power. Gotenks goes into training, and Piccolo tricks Buu into waiting in a room in which time moves slower than the room Gotenks is training in. Chichi starts to scold Buu for killing so many innocent people. Buu turns Chichi into an egg and squashes her (THANK GOD!!).
Buu eventually gets sick of waiting for them to come out and demands to be taken to the boys. Piccolo takes him into the room and Gotenks battles with Buu for a while. The fight reaches a stalemate when Piccolo blasts the door to trap everyone in the room, so that Buu cannot kill anymore people. Buu uses his power to create a portal and exits the room. Gotenks tries and fails to make a portal but then goes SSJ3 and has the power to pull it off. Gotenks battles Buu in his new form and is winning and knocks Buu back to the Earth, however, Kame's Lookout is destroyed in the process. Gotenks and Piccolo go back to Earth to look for Buu's body, but find that he is far from dead. Before Gotenks can continue his attack the Fusion wears off and Goten and Trunks unfused are not strong enough to stand against Buu.
Gohan finishes his training and puts on a suit like his Dad's before leaving to help his friend's on Earth. Goku wants to go help but cannot because he is dead. Gohan appears on Earth and battles Buu until Buu self Destructs and the Z warriors think they have won. The fly away and see Buu flying at them. Goten and Trunks fuse into Gotenks again, but while Gotenks is distracted Buu absorbs him. Now much stronger than before, Buu launches an attack against Gohan. Buu throws a fireball at Gohan but it is blocked by another Fireball thrown by Tien.
Goku is brought back to life because Dai Kai-oo-shin trades his life for Goku's. Kai-oo-shin gives Goku the Fusion Earrings and shows him how to use them so that Goku and Gohan can fuse and beat Buu. Meanwhile King Yama grants Vegeta life so that he can help save the Earth. Just as Buu is about to launch another fireball at Gohan, Goku appears and save the day, cutting Buu in almost in half. He gives Gohan one of the earrings and they prepare to fuse. Just then, Buu's dissected parts start to absorb some of the Z warriors (Piccolo, Tien, and even Gohan.) Buu is now fully powered up and Goku is feeling hopelessness weigh down on him.
Here comes Vegeta!!! Vegeta shows up to help Goku (this is a first! :) ), and Goku tells him about the fusion. Vegeta finds the earring that Gohan dropped and puts it on. Goku and Vegeta fuse to form Vegetto. Vegetto beats up on Buu for awhile, but gets absorbed on purpose to rescue his absorbed friends. Vegetto's fusion is canceled out by the absorption and Vegeta and Goku go off to search for their friends. Piccolo, Gohan, Trunks, Goten, Goku, Vegeta from Buu's pores and are returned to normal size. Buu has, however, absorbed enough energy to reach his original form, and Buu is now whole again. Buu launches a fireball that will destroy the Earth and with the help of Kai-oo-shin, Goku teleports Vegeta, Goten, Gohan, Trunks, Piccolo, Mr. Satan, and Dende to Kai-oo-shin's planet where they escape the Earth's destruction. Buu teleports and follows the escapees. Goku fights Buu and is beaten badly, then Vegeta steps up and is beaten also. Buu is about to kill Vegeta when Mr. Satan taunts him and draws off his attentions. Good Buu escapes from within Buu and the two fight until Good Buu is knocked out. Buu continues to fight Goku and Vegeta. Vegeta tells Kai-oo-shin to gather the Namekian Dragon Balls and wish back the Earth and all its inhabitants. The only people left now to face Buu are Goku and Vegeta, as everyone else was sent back to Earth. Vegeta distracts Buu while Goku builds up his Spirit Bomb. The heroes back on Earth try to convince everyone to raise their hands and donate their energy to Goku's Spirit Bomb, but none listens. Then Mr. Satan, who is still a hero to the people, raises his hands prompting everyone else to do the same. Goku is now ready.
Goku launches his Spirit Bomb, but Buu holds it back. Kai-oo-shin makes his final wish and restores Goku's energy so he can increase the strength of his Spirit Bomb. Buu is destroyed the the Z warriors are victorious. Fat Buu awakens and his life is spared for saving Mr. Satan's life earlier. Fat Buu joins the Z warriors.
Goten and Trunks are teenagers (still making trouble). Gohan marries Videl and they have a daughter named Pan. Buu becomes Ubuu, a purely good version of Buu. Goku trains Ubuu, and all is well