Ive been thinkin' about...
The first game had Heartless, the second had Nobody, now we get Unbirth...

But think:
Heartless HAVE a only a heart
Nobodies HAVE a only a body
...Then what can this thing be?

I read on GameFaqs.com's Forum, there was a guy who said this:

-What if an unbirth, as it were, were simply a pure darkness, uncreated by any man, and had no human qualities attached?

If the equivalent to an unbirth, pure darkness, were to arise in a human's heart, and were to lay dormant as it grew ever stronger in its slumber, it would eventually create a heartless - a sort of Birth by Sleep.-

I kinda agree with him, but we have no proof at the moment.

Please post what you know/think about Unbirth

The Unbirth can be that so u have a pretty good guess

Hmm.. That is something to think about. xD lol I'll get back to you on this.

Interesting~ o-o

...? Again?