I don't want to go into a bunch of plot details, namely because I don't actually have a plot yet, but in my mind the theme of the story is transformation. The magic system is transformational (you can turn something into something else, but only if you actually have that something already on hand. There's no creating something from nothing... it's all about balance, transference, etc) and I want the main characters' arcs to reflect that as well.
Anyone have any random ideas?
Crap, I need to go to bed.