I guess in a very broad sense XII is about Freedom. i personally always saw it as overcoming your past. Even the Occuria enforce this theme as, unlike other such godly beings, they don't really do much. Their power is all in the past and that is how they act. In terms of our human heroes and villains, they each must come to terms with their suffering in order to do what is right. It's present and clear in everyone from Ashe to Gabranth.

But, as I said, this could be interpreted as Freedom. Sort of breaking the chains/tiesof your past.