Inspired by other recent threads, we have a triple thread version!
Round 1: Donquixote Doflamingo vs. Zommari Rureaux vs. Sasori
For the first round, we have the puppet masters! We've got Sasori, who brings his own minions to the fray. Doflamingo, who has to improvise his minions, but can fight without them too. And Zommari, who eschews the strings altogether to jack his foes minds!
Round 2: Jinbe vs. Tier Harribel vs. Kisame Hishigaki
Perhaps the most obvious of the match ups, the fish folk go at it second. We've got good variety in the fighting here. Jinbe is a largely close up fighter, while Harribel can fly and has the best range game. Finally, Kisame has the best mixed range game of them.
Round 3: Bartholomew Kuma vs. Barragan Luisenbairn vs. Obito Uchiha
Here we have quite possibly the most hax of the powersets in this match up in Respira, alongside a still hax but significantly less hax pair of partners in Obito and Kuma.
Round 4: Trafalgar Law vs. Ulquiorra Cifer vs. Itachi Uchiha
Here we have a battle of the super popular characters. We've got one of the most destructive participants present in Ulquiorra, while Itachi has a high degree of Hax via his Genjutsu. Law meanwhile has some useful but not debilitating abilities.
Round 5: Yammy Largo vs. Gecko Moria vs. Pain
Two Giants, two Masters of the undead, and two leaders(?)
Round 6: Boa Hancock vs Grimmjow Jaegerjaquez vs. Kakuzu
Here we have what is likely the most straight forward of the match ups. Two largely physically minded fighters and one with some range but nothing super hax
Round 7: Buggy the Clown vs. Nnoitra Gilga vs. Hidan
Two Scythe Users and a man who can't be cut.
Round 8: Bartholomew Kuma vs. Starrk vs. Deidara
These all do explosions well. Who will do them the best?
Round 9:Crocodile vs. Szayelaporro Granz vs. Orochimaru
Two Mad Scientists, and the first of their groups to be faced by the protagonists
Round 10: Blackbeard vs Sosuke Aizen vs. Madara Uchiha
Finally, we have the men who betrayed their groups, while also be ostensibly the most powerful of them.
Bonus 1: The winners of each bout face each other, teaming with the others of their group of course
Bonus 2: All ten of each group go to war with each other
Bonus 3: They sit and Talk.