This is a tale of what would have happened if Vegeta never fought Majin Buu. After his rematch with his long time rival, Vegeta managed to knock out Goku, but he himself was unable to stay conscious and fight Buu himself. With no one to stop him after Gohan and Dabura failed, Buu went with Babidi to begin his destruction on Earth.
He and Babidi were about to leave to another city before Buu looked to see Goku appearing out of nowhere behind him.
Meanwhile, Bulma was trying to get her stubborn parents to leave when the ground began to shake, it was Goku fighting Buu as a SSJ3.
Trunks and Goten were trying to help her escape before Goku crashed through the window.
"Bulma! You have to go now!" shouted Goku, as he saw Buu fire a pink beam at him, and much to Babidi's surprise, Goku deflected the attack and the beam actually hit Buu, and was turned to chocolate.