My friend who recommended this game to me vehemently made the point that is a game with a big cast for a reason: the fact that there isn't a "main character" per se but little stories to make up a big one. I would say Terra is the central character in the heart of the story (esp. in WoB and the Mobliz side story) and Celes' segment in the WoR is significant to the plot as she begins to round up the cast again a year later after the disaster. But the characters each have their own contributions to make the beating heart of the plot, their reasons to fight etc etc. That's what makes FFVI wonderful, especially when on the buildup in returning to Narshe, you get to see the scenarios of Locke, Terra/Edgar/Banon and Sabin. I think that part works perfectly in not focusing too much on just one character and giving everyone their moment in the limelight.