Not everyone can take the pressures of being one of Death's apprentices. Like soldiers drafted into war, there is no choice, you have to do it. No matter where you come from, how rich you were, what class you were in, who you were.
And just like soldiers, some of them go AWOL, desert from duty rather than face it or, even worse, become traitors, using the knowledge of Death to save lives instead of taking them or in extreme cases, spend your time hunting your fellow apprentice.
Sometimes it's a slow descent, you don't mean to but you start helping more people than you cut. Or, one day, you just walk away from Death's HQ and never come back. Or sometimes it's a breaking point. After years of loyal work, something snaps inside you... the inhuman-ness of this all- being asked to take lives and bare witness to death of hundreds. You can't watch an innocent girl die again. No no no, you can't. YOU JUST CAN'T.
Either way, you will be labeled a 'Fallen', an apprentice whom abandoned their duties and take refuge in the living world (often times with spiritually-aware humans).
The punishment for going AWOL is similar to military desertion. You are to be caught and then taken back to the HQ for juridical punishment, the judge being Death herself. If you resist, you will be killed on the spot.
And being killed as an apprentice is a different beast than normal death. An apprentice is caught between the world of the living and the death, in-between the cracks as you will, stuck there like an awkward pebble. If you die as an apprentice, instead of ascending to a higher plane, you fall between the cracks into nothingness and void. Your body will dissipate, your severed soul burned into nonexistence. You will never see your family and friends again. You will never see anything again.
Just the thought of that keeps most apprentices from deserting their duties.
But not all.
A fallen apprentice will also be playable I think, along with spiritually-aware humans and normal apprentices.
...Man I'm thinking about this group as if it was actually going to be a thing. *laughs hollowly* But I want so badddlyyy. So much want....so much waaannntttt.