Wow, this is good. I've always liked the "Rinoa = Ultimecia" theory (it's fun!), and the way that idea is used here rocks me. The blurring of identities is nicely haunting.
Another thing that really works for me is the formatting. I'm not a huge fan of formatting tricks in general, but they don't feel at all out of place here, and they augment the story. Nice!
And the last line of this fic is just perfect.