Maria, upset that Celes stole her Opera Gig. So she plotted an elaborate revenge scheme where she plans to steal the identity of each party member, even learning their unique skills. The plan goes out the window when the world is destroyed, and she realizes defeating Kefka might just be a tad more important. The PROOF is in the ending. Who does Gogo mimic when they're escaping, and have to press the button at the same time? That's right! Celes.