Opening this kind of battle arena is just asking for pure insanity! Give me a second...
Seed (Rogue Galaxy) vs. Ichigo w/Tensa Zangetsu (Bleach)
I'm not sure who would get the win in this one, because they both move fast, have thin black swords, and wear masks most of the time. It would most certainly be interesting.
Kuchiki Byakuya w/Senbon Zakura but not Bankai (Bleach) vs. Sabaku no Gaara (Naruto)
This would be more of a special effects show than anything else, but it would be fun to see.
Gotei 13 (Bleach) vs. Organization XIII (Kingdom Hearts) OR Las Espadas (Bleach) vs. Akatsuki (Naruto)
Come on, you know you want to...
Zegram Ghart (Rogue Galaxy) vs. Auron (Final Fantasy X)
They have basically the exact same fighting style, but I'm going to have to give this one to Zegram just because of all the Revelation techniques that give him the magical edge. One could argue that Auron is theoretically capable of every attack in FFX, but that's quite frankly a load of bull****.
Asakura Yoh w/Spirit of Sword (Shaman King) vs. Haru Glory w/all Ten Powers of the Ten Commandments (Groove Adventures RAVE)
Just who can pull more insane sword-based powers out of their ass? I honestly don't know who could win this one, I think that in the end it depends on whether or not Silfarion moves fast enough to escape Yoh's perception. This is assuming that we waive the "Only Oversoul can damage Oversoul" thing.
Kiba (Wolf's Rain) vs. Sacred Wolf Link (LoZ: Twilight Princess)
Would that count as an illegal dog fighting ring? I think that without Midna helping him, Link would collapse in minutes.
I could go on....but I won't