This is the third fighting game I'm checking out for the WonderSwan Color and just like the other two I played (Ultraman en Kinnikuman Nisei Dream Tag Match) the title of this game is incredibly dumb. I guess it aims at the place where the fights are fought (Grand Battle Swan Colosseum) and it makes very clear that this place doesn't consist out of multiple pieces (or something). I'm not sure of course, since the whole thing is in Japanese.
One Piece Grand Battle Swan Colosseum - try saying that ten times really fast - is your average Street Fighter clone, but with a little twist. The twist is that the fighting area's are really large - actually they're so large the screen scrolls from left to right or vice versa while fighting. They aren't completely horizontal either: there are higher area's you can jump on and objects you can use. Furthermore, the cast consists out of seven wacky characters. The main character is Luffy, a kid with a straw head and elastic arms, like Dhalsim from Street Fighter. Another noticeable character is Chopper, a sort of dwarf reindeer with a backpack.
The graphics in One Piece Colosseum are very bright and the audio and controls are decent, though the whole thing feels a little slow. My main problem was that the fights take forever, because the life bars are huge and none of the hits seem to do very much damage at all.
Overall, One Piece Grand Battle Swan Colosseum is an okay game, but it just couldn't hold my attention for very long and it can get a little boring. Nevertheless, it's a lot better than the terrible Ultraman game. But the best fighting game for the WonderSwan Color is still Kinnukuman.