Yuffie is a 16 year old ninja who is also really good at being a thief. She used to pick on innocent travellers until she tried it on Cloud's party and got her butt kicked. She wound up joining them though, with very selfish motives.
I really hate Yuffie. She hassles you needlessly by stealing your stuff and is just a real bitch. I don't use her at all because she sucks at physical attacks and I don't trust her with my Materia. The only good thing about her is that her Limit Breaks are powerful. Her level 4 limit break, All Creation, can be obtained by fighting and defeating her father at the top of the Pagoda of the Five Mighty Gods. Her Ultimate Weapon, the Conformer, can be found in the generator room of the crashed Gelinka. I can't tell you much more because I didn't use her much, and when you play the game, you'll see why.
