The term for what Zeke and his brethren are. There are roughly one hundred known species of demons who are beyond the abilities of the Hellchasers to battle and banish. Those who have origins so powerful and old that they have been sealed away and are supposed to stay in respective holes.
For that level of demon, they need nuclear-devastation capabilities. And only one of this ilk can battle them and put them back in their bottles without dying in the process.
Loosely translated, Necrodemian means death to demons or demon executioner. Unlike a Hellchaser, they have the ability and authority to kill demons without consequence as long as they follow certain protocols. Hellchasers can only send demons back to their dimensions, and are working on regaining their own souls and redeeming themselves. Necrodemians are chosen by the higher order of angels to be protectors and to execute certain breeds of demons determined too dangerous to continue living.
The average life expectancy for a Seraph/Necrodemian is two years. And the difference between a Seraph and an Arel is that they are born from a specific bloodline, the Arelim aren’t.
Once chosen (usually after one of their bloodline is killed and the medallion passes down to them) and they decide to accept their Seraph medallion and Seraph sword, they can’t undo it. Their appointment is to the death. And they can only die by a demon blade. They will not age until the moment of death.
They answer directly to Gabriel and Samael, but are subject to the censure of any archangel.