Why is she here? Celes is woman extraordinaire. She was a general in league with Emperor Gestahl in the beginning, then turned into a spy, and then becoming a saviour of the world. Add opera singer to that and you've got yourself a pretty impressive woman. Besides that, she's the 'work hard no matter what the situation is' type of a person. Look at how well she took care of Cid, catching fish just for him every minute (ok, so Cid might die if you keep feeding him rotten fish, but don't count that......).