"The Ultimate Fighter" (天下無敵の合体おとうさん Tenkamuteki no Gattai Otōsan, lit. "The Fused Fathers are Unbeatable") is the three hundred tenth chapter of Dragon Ball Z and the five hundred fourth overall chapter of the Dragon Ball manga.
The newly formed fused Potara warrior decides to name himself Vegito (Vegerot in the VIZ edition), combining the names Vegeta and Kakarot together, the two warriors who created this fusion. Immediately after deciding on his name, Vegito transforms into a Super Saiyan, calling himself Super Vegito. Super Buu however, it not afraid of this new warrior, and immediately begins to charge towards the warrior at full speed. Super Buu fires an Energy Sphere towards Vegito, only for Vegito to easily deflect it back with one arm, with the ball returning to Super Buu, barely missing his head. Despite Vegito's skills, Super Buu still believes he still has the advantage, and once again rushes towards his target, claiming he'll never destroy him. Immediately though, Vegito delivers a powerful kick to Super Buu's nose, giving him a nose bleed. Vegito comments that it would have been better if he did not have a nose, such as before absorbing Vegito's friends and family, Piccolo, Gotenks and Gohan. Super Buu replies by stating the more Vegito angers him, the more Buu will make sure Vegito suffers a truly painful demise. However, Vegito quickly strikes back with a powerful punch, before grabbing his leg and flying down towards the ground, throwing Buu into the rocks below. Meanwhile, on the Sacred World of the Kai, Kibito Kai is amazed at the power the Potara earrings have managed to give to the two Saiyans, with Old Kai commenting that Kibito Kai is foolish and that Vegeta and Goku already have enormous power, but just needed to combine it and properly work together. Back on Earth, Vegito lowers his right arm towards the ground, and from his hand a large beam shoots from it, impaling Super Buu, as Vegito raises him from the rubble back into the sky. Vegito now requests for Super Buu to fight with all his power, and if he already has, he is extremely disappointed by the results. As Buu regenerates and escapes from the beam, he starts to become incredibly frustrated, blowing thick layers of smoke from his head. Super Buu comments that now, even if Vegito is too strong for him, he can not attack Buu because the smoke is far too thick to see anything. However, Vegito still gives Buu a brutal pounding, managing to tear off his antenna. Vegito comments that just watching your opponents with your eyes is not enough, you need to feel their energy. Old Kai begins to become annoyed at Vegito's playful nature with messing around with Buu, and orders him to finish him off. Buu curses the Saiyan fusion as he regenerates back his antenna.