Demonic Conversion

A demonic conversion is the name given to the ritual where mortals, half-demons and other beings can become pure demons. If a conversion is complete, its possible that it may destroy the soul, leaving them unable to feel emotions like love. Conversions can cause physical changes, as seen with Sirk. As he gained a more reptile-like appearance when his conversion advanced. When a conversion is complete, it cannot be reversed.

Demonic Training Program
Mortals are recruited into a Demonic Academy and are put through a brutal training program. They earn chevrons which represents the status of their conversion. The mortal has to kill another mortal for their conversion to be complete.

Killing Mortal Relatives
The half-demon Sirk, killed each of his mortal relatives so he could become a full demon. With each kill he would gain another power until the his last relative had been killed. During the conversion, he'd lose his mortal appearance and would turn into his demonic self.