Anomaly - Ghosts

To keep things simple:

The word "spirit" could mean both the idea of a ghost and the actual physical spirit inside someone. To prevent confusion, "spirits" will refer to the physical thing everyone has, and ghosts will refer to the spirits walking around without bodies.

Ghosts are the spirits of dead people. They roam the earth, searching to finish their business before leaving for the afterlife. People who die of natural causes, or die satisfied do not become ghosts, they exit and go directly into the afterlife. That said, there has to be a lot of anger, resentment, despair, or paranoia to keep your spirit on earth.

Ghosts are semi-transparent, and glow the color of their soul. Their eyes lack pupils and irises; their eyes are entirely their white sclera.

They are very skittish and scared, they tend to hide their forms from humans. Usually, they interact with things indirectly, can cause wind, changes in temperature in a room, can incite emotions in others, etc. Ghosts feed off of indirect energy; being around humans and animals gives them fuel to not disappear. This energy doesn't make the living beings wilt, but rather they might need to eat more or they'll feel drained.

A ghost, if brought even deeper despair, depression, or anger, can become a demon. No spirit can remain on the physical realm forever without becoming a demon— the stress from merely existing will make any of them turn.

The only way ghosts can leave the physical world is if they leave their final will and worldly desire behind. By wanting to continue, or to finish things, they are binding themselves to the earth.

When they let go, they disappear, exiting the physical world.