"The Terrible Mystery" (恐るべき謎 Osorubeki Nazo, lit. "Fearsome Mystery") is the two hundred fifty first chapter of Dragon Ball Z and the four hundred forty-fifth overall chapter of the Dragon Ball manga.
As they fly along with Gohan's stolen energy, Yamu thinks they can revive Majin Buu and Babidi will be very pleased as well. Supreme Kai is in pursuit, from a safe distance. Back at the tournament grounds, Videl rushes over to Gohan, as Krillin says he'll go with Goku, but first he'll tell his wife. Vegeta tells Kakarrot not to screw with him; what about their fight? Vegeta doesn't care about Supreme Kai or whatever, he just wants to settle their score, one-on-one. That's the only reason he came to this stupid tournament. Goku says they can fight afterwards, but Vegeta reminds him that he's only here for one day. Goku suggests to Vegeta that he should come with them just in case. Piccolo is the first to fly off, and Goku goes to make sure Kibito will take care of Gohan. With Kibito's assurance, Goku flies off as well, followed by a reluctant Vegeta. Android 18 says she's staying here so she can get the prize money. Kuririn tells her not to kill anyone, and No. 18 tells him to run away if it seems too dangerous, as he flies off.
Videl asks Kibito where everyone went, and he says she'll know if she goes. Some doctors come to help Gohan, but Kibito tells them to shut up and watch. He puts his hand on Gohan's chest, and begins healing him, contemplating all this unfathomable power and pure energy Gohan has. Goten and Trunks are watching from a roof, wondering what was up with Gohan, and why everyone flew off. Gohan is finally fully healed, and Kibito says he'll tell him everything if he comes with him, and then flies off. Mr. Satan notices that Videl is with that kid again, and gets pissed. Videl wants to go too, but Gohan says only if she promises to run away if things get dangerous. Gohan and Videl then fly off. Satan sees this, and says that Videl has become a hikō girl. (Hikō means "flying", but also "delinquent". It's a very bad pun.) Bulma, Chi-Chi, and Yamcha wonder where everyone went, and the announcer is worried about the World Martial Arts Tournament.
Piccolo, Vegeta, Goku, and Krillin all catch up to Supreme Kai, who grateful for their help. Goku wonders if he can't those two but Supreme Kai tells him they're just being used by a sly mage. Long ago, when humanity had just begun to walk on two feet on Earth… Far off in space, there was a very evil mage named Bibbidi. One day, Bibbidi unintentionally created an incredible monster. A majin called "Buu". Majin Buu had no reason or emotion. He did nothing but destroy and massacre repeatedly. He was a monster born only to bring terror. In a matter of years, hundreds of planets were turned into planets of death. Vegeta thinks that the Saiyans did the same thing. Supreme Kai tells him there were five Supreme Kais back then, who all held ability to defeat someone like Frieza. Vegeta is shocked to realize he read his thoughts. Four of those Supreme Kais were killed by Majin Buu, who's ferocity was controlled only by Bibbidi and temporarily sealed away Majin Buu when he needed a rest.
Meanwhile, Kibito is telling the same story to Gohan and Videl. Bibbidi brought the sealed up Majin Buu to Earth, because that was his next target. Supreme Kai was waiting for this chance. And so, before Buu's seal was released, he was able to kill Bibbidi. The ball in which Majin Buu is sealed has remained sealed, without being destroyed. They thought it best to not unnecessarily disturb it. Moreover, the only one who could release the seal was the Mage Bibbidi. However, just recently, they learned something terrible. Supreme Kai finishes the story: "The Mage Bibbidi had a child with an evil heart, just like him. The mage Babidi".