Death and the Afterlife

Death is a complex topic in the world of Nailara. The path a soul takes when a creature dies can be complex, and rarely do two souls take the exact same path. When powerful entities such as gods or demons get involved the path to the afterlife becomes even more complex.
When mortals speak of the afterlife, they often conflate two distinct things. The 'afterlife', which is generally referring to everything after a mortal's life on the material plane. And then, after the afterlife, a soul is returned to the Void.

Afterlife

When a creature dies, its soul separates from their body, and finds itself in the Border Ethereal.
The souls of the devout are often claimed by the gods they worshipped and brought to their gods realm. Their fate then is up to their god - some are resurrected to live in service of their god, or rest in reward for their service. Others are crafted into powerful servants, celestials.
The same can be said for if a soul is claimed by demons - though, it is perhaps a far less desirable outcome. Wayward souls claimed by demons are torn apart and used as fuel to create their demonic armies.
Psychopomps are protectors of wayward souls on their journey to the Void - from both gods and demons. Some refer to them as the guides of the unwanted, those who are not important enough for anyone else to claim. But in truth, psychopomps are even known to guide the souls of deceased gods.

Wayward Souls

Wayward souls are the souls of mortals who have died, and have not yet been claimed by another entity or found their way to the Void. When a creature dies, their soul manifests in the ethereal plane.
A soul's consciousness is known as its mindscape, and with the proper magic it is possible to manifest oneself in a soul's mindscape. There, they can interact with the wayward soul. Demons use this to make deals, and gods contact their deceased worshippers in this method.
The longer a wayward soul exists, the stronger its mindscape becomes. At some point, it can actually become impossible to contact through normal means. Those that are even stronger can begin to manifest in the ethereal plane - or the material. Ghosts are one such sort of wayward soul - whose unsolved issues in life gave them enough motivation to resist the draw of the Void. Over time, they lose themselves.
Resurrection magic only works on wayward souls - a soul that has been claimed, destroyed, or passed on to the Void cannot be resurrected.

The Void

All wayward souls are naturally drawn to the Void. It is not a location as much as it is places where the walls of the ethereal plane thin. Souls which cross over into the void are gone - even beyond the reach of the strongest resurrection magic, and the gods themselves.
No one truly knows what lays beyond the Void, or if it is simply oblivion. Many assume that the Ancient Ones who designed the universe know, but if so, they have not divulged this information.
The Void has many names across cultures.

Undead

Undead are creatures whose souls have been bound after death, preventing them from being drawn to the Void. In the most technical sense, many celestials, demons, and servants of the gods are undead - those who have entered the afterlife but were transformed or returned before entering the Void.
Generally this term is reserved for a specific sort of creature - those whose consciousness inhabits their corpse, rather than being transformed or returned to life.

Type

Natural