Ehrgeiz was an under-appreciated fighting game released by Squaresoft somewhere around 1997 - 1999. I think it was one of Square's first ventures into this category. The storyline was pretty basic.. A powerful weapon is found in ruins and desired by fighters. A mysterious organization holds a tournament with the EHRGEIZ weapon as the prize. Aside from fighting, there were sidestories and minigames. Personally, I loved EHRGEIZ. But it didn't become too popular.

Yuffie appears as a playable fighter/guest character. Guest characters are mysteriously summoned from the FF7 world with little relation to the storyline but to fight. Some will only become available after certain conditions are met. Other guest characters that appear are Cloud, Tifa, Sephiroth, Vincent, and Django(who bears a striking resemblance to Red XIII).

Wanna get Yuffie? Beat the game with Tifa, and you will unlock her! Yuffie uses her shuriken in battle; she can also hurl throwing stars at her opponents, and do cool flips in the air. All of the FF7 characters are excellent fighters in the arena.