Genetics of the Species

Every Species can be determined by a certain genetic makeup. The features that are being looked at is the Blood, the Cover and the Core. Each of those can either be demonic or angelic. Demonic and angelic do not stand for bad and good in this case. None of those features can be changed. 
Core The core could also be described as the soul of a person. It determins in which world the person can live. People with an angelic core can live on Earth and people with a demonic core can live in Degheich.
Cover The cover determins whether someone can change their appearance / shapeshift or not. A person with an angelic cover cannot shapeshift, a person with a demonic cover can.
Blood The blood of a person is relevant in medical contexts. Also, vampires can only drink angelic blood.