Super Buu's origins are identical to his mainstream Dragon Ball Z counterpart until his battle with Gotenks. Instead, when Buu is faced against Ultimate Gohan and Gotenks simultaneously, he decides to absorb Gohan first, unlike his mainstream form. Following his absorption of Gohan, he allies himself with Nagato and Sosuke Aizen when they attack the joined alliance of the Z-Fighters, Konohagakure, and the Soul Society. When the forces of Shinigami, Shinobi, Saiyans, and Z-Fighters team up to opose him, Buu manages to dispatch of many before being forced to retreat. Seeking more power, he absorbs Nagato and Pain's Deva Path, and moves on to attack Konoha where he comes across Goten, Trunks, and Konohamaru. The three fuse into Gonohamarunks to combat Buu, but now, under the name Majin Bain, he proved to be more than a match for them. Vegeta and Sasuke Uchiha, after a battle with Naroku, fuse into Vegesuke to assist Gonohamarunks, but are also defeated after Sosuke Aizen is absorbed. Now fused into Majin Bainz from absorbing Nagato, Deva Pain, and Aizen, Buu seemed to be unopposed until Naruto Uzumaki, Ichigo Kurosaki, and Goku emerged from the Hyperbolic Time Chamber, now fused into Goruchigo. They where evenly matched, even when Goruchigo was in the Super Mugetsu Sennin 3. Goruchigo finally used his ultimate technique, Final Dragon Fist Shuriken. The attack ultimately kills Majin Bainz.
FormsHe has many forms due to his absorptions.
Base Form: His original body. He appears as he does in the mainstream Dragon Ball universe. He retains his original appearce on no shirt and white pants with a belt bearing an "M".
Gohan Absorbed: As with his mainstream counterpart, Buu absorbs Ultimate Gohan, although this time around, Gohan is his first absorption. He appears wearing Gohan's gi and undershirt.
Nagato & Deva Path Absorbed/Majin Bain: Absorbing Pain's Deva Path and Nagato, Pain's real body, Buu now wears Akatsuki robes and has obtained Rinnegan in both his eyes. Unlike his mainstream version, his clothing takes on his newest absorption and the one before it, which means he still wears Gohan's gi underneath his Akatsuki garb.
Sosuke Aizen Absorbed/Majin Bainz: After absorbing Aizen, Buu now obtains his Espada cloak and light purple eye color, while still retaining Nagato's Rinnegan. He no longer wears Gohan's gi or an Akatsuki cloak, but instead has bandages on his wrists and lower waist. Looking less like the Deva Path, he now takes on a more Nagato-like appearance, with several of Nagato's black spikes protruding from his back.