Board Thread:Theories Discussion/@comment-4875891-20121210230315/@comment-6192846-20130610013753

Currently, we are being very hands-off on making any assumptions since so many theories exist for what exactly an awakened vessel is. As for personal opinion, I think they are supposed to be the Demons of Sin that take on human forms.

My reasoning is because the Demon of Gluttony is depicted as the Master of the Graveyard and is actively planning for its vessel to awaken, wanting to use Hansel and Gretel for whatever reason (I have elaborated on the possible connection here) in preparation for that.

Similarly, the Master of the Graveyard is described as a "phantom" born from the glass and given other descriptions that imply a more supernatural source than just a human soul in a vessel. That still doesn't explain a lot of the others though so who knows what the truth is. I think it might just be a case-by-case basis and that the awakened vessels don't have a universal explanation for "who" they are.