Himura Kenshin, Shinomori Aoshi, and Hajime Saito, and, if you were going to include them, also Seta Soujiro and Makoto Shishio all use different sword styles. Kenshin's style is heavily based on the battojutsu, the quick-draw technique, Aoshi's is a speedy style that combines martial arts prowess and two blades. Saito's is heavily reliant on the Gatotsu thrust attack and variations thereof, Soujiro's is mainly based on speed, and Shishio, as far as I can tell, is based on fire attacks. Be that as it may, Rurouni Kenshin is a series that's primarily realistic, with some superstitions and allowing people to do things that aren't really possible. However, it wouldn't stand up to most of the other beings, they're just too weak to compete with the others.

Bison's relatively powerful, but he doesn't compare to some of the other characters in terms of strength.

If you want to make this game, I say you make it like Marvel vs. Capcom or Smash Bros., where all the characters are immediately set on an even playing field regardless of power levels. For example, Samus's suit could easily beat just about any enemy, but on Smash Bros., she's on par with all the other characters. Same goes for characters like Akuma and Bison in Marvel vs. Capcom, they have some nice moves, but they can still be beaten.