I imagine the factions would be aligned to each Crystal. So there'd be the Fire Crystal Warriors, Water Crystal Warriors, etc. Each crystal would have some sort of guardian which would serve to both protect the crystal and guide the Crystal Warriors (sorta like Cosmos and Chaos). 

I s'pose you can all start claiming dibs on a character now if you'd like. If I can get a little more interest, I'll get the game set up and we can start sometime this week.