Having been defeated easily by Majin Buu in their first battle, Trunks and Goten practice the Fusion Technique with renewed vigor; Mr. Satan emerges from his training facility and goes to Majin Buu's house; Old Kai finishes his ceremony to awaken Gohan's sleeping powers.
Start of the "Fusion Saga". In a rage, Mr. Satan fights the two thugs. Majin Buu heals the puppy, rebuilds his house, and relaxes with Mr. Satan. Gohan grows impatient with waiting, and he tells Old Kai about Bulma. One of the thugs comes back to cause trouble for Majin Buu and Piccolo scolds Trunks and Goten for being gone for too long.
Gotenks uses the Super Ghost Kamikaze Attack against Majin Buu; Goku can't sense Gotenks' or Majin Buu's energy, and he realizes that they're fighting in the time chamber; Mr. Satan and Bee wander the desert and think about their time with Majin Buu.
As Majin Buu continues to fight Gohan, he realizes that he can't win, so he self-destructs, hoping to take Gohan with him. Afterward, Gohan, Piccolo, Goten, and Trunks search for Dende, and they find Mr. Satan and Bee wandering in the desert.
Vegito continues fighting Majin Buu, who is getting frustrated and is using the special attacks of the people he has absorbed. In Other World, Videl tries to convince everyone that Gohan is still alive.
Vegito is turned into candy by Majin Buu, but he continues to fight; King Kai considers sending Krillin and Yamcha back to Earth to help in the battle; King Yemma tells Fortune Teller Baba the story of how he convinced Vegeta to help.
Goku and Vegeta befriend a family of worms living inside Majin Buu. They continue searching for Trunks, Goten, Gohan, and Piccolo, but instead they find versions of them that Majin Buu has created in his mind, and they must fight them. Meanwhile, Majin Buu eats everything he can find.
Mr. Satan tries to convince himself that everything that has happened is just a dream; Majin Buu destroys lots of planets while looking for Goku and Vegeta, who are trying to form a plan revolving around the use of the dragon balls.
Vegeta calls upon Earth's population to give up their energy to Goku, who begins charging his Spirit Bomb. Meanwhile, good Majin Buu continues to fight evil Majin Buu. Also, the people of Earth celebrate their new lives.