A little off topic, when I first saw screenshots of Birth by Sleep, I thought Terra (without his armor) looked like Zack and thought I had saw the first FF cameo for the game...

I thought, I remember both games stating that the Heartless existed before Ansem's experiments as well.

Its weird how the Unbirths (at least from the few small screenshots we have) look surprisingly similar to the Heartless, so part of me wonders if there is more of a connection with them. Perhaps an Unbirth is a strain of Heartless that had hearts so strong they were changed differntly when attacked by Heartless? Becoming something else rather rather than a Heartless. I just wonder cause usually the names have significant meaning and Unbirth sounds like a reversal of a process rather than a Heartless who seeks Heart, and a Nobody who seeks an identity.

Just an "out there" theory...