In this world is divided into four realms with each being inhabited by a different species. There is the living world with humans, purgatory with undead, heaven with angels and hell with demons. They are all connected by Energy wich runs through every living being in some way. When it gets a personality and a mind of
its own a soul is created and every human has a soul, its what gives them life and keeps them from being empty shells and it gives demons fuel to grow and become stronger.
when humans die their soul travels through purgatory where it gets purified. that means the personality and memories get stripped from it turning it back into energy wich then gets redistributed back into the living world by the angels.
Angels do not have a soul or feelings. Their only purpose is to serve the cycle and protect it and their appearance is hard to comprehend for any mortal.
Purgatory isnt technically a full realm but more of a mirror image of the living world which immediately splits any soul from its host that enters. Nothing alive can exist there not even plants and it looks exactly like an empty version of its counterpart so it mainly functions as an in between or a gateway than a world with true habitants. Altho it is possible to live in it.