Birth by Sleep Unbirths

Ok I know in BBS has unbirths in it but what the hell is so important about them? I mean what 'Big' role do they have in BBS? How were they created? Also where are the heartless? What I don't get is why Nomura (If thats how you spell his name) made Unbirths, what is so important about them? I would really, really like to know.

 

They're not called Unbirths, they're called Unversed. Unbirths was a translation error.

It has been revealed that the Unversed are dark beings created by Vanitas. As a human created from the purest, most raw form of darkness, Vanitas had the ability to manipulate the negative thoughts and emotions of people, and spawn them as the Unversed to further his goals, as well as Master Xehanort's goals. By every and all accounts, the Unversed are extensions of Vanitas himself, and part of his power and influence - effectively making him the "first and original Unversed". With Vanitas's destruction, however, the Unversed are completely wiped from existence.

 

Thank you!