Terra is not the main character. She didn't play much of a BIG part at the ending...it just that she remains as a human instead of an Esper and increasing knowledge for us to know what will happen to Half-Espers like Terra. Note that Terra is skeptical of her abilities at the start, unlike all main characters who were confident the whole game. Terra IS the main character because she holds the key to the Returners success (or so they thought.)
Locke IS the main character because he, like most main characters, have a girlfriend (ok, make that two). He is also the main character because he simply seemed to be the leader of every journey (making him a big cast in WoB), In the WoR however, his role reduced to just a...thief?
The support characters (they helped greatly and plays a decently good prat in the game) are: Edgar and his Figaro castle, Setzer and his airship (reputition increases in WoR).
Celes is just a character for Locke, to increase the love scene in FFVI. Shadow just increases the secrets of a family, which seemed rather amazing. Relm, like Shadow, and Strago is just ... well... he led the party to the statues.
GAU may be an important character considering the "shining treasure" that he found. :/
Sabin help to make the battle system more interesting. Cyan is for those gamers who loved Katanas (Masamune).
