In the Runaway Kids universe, a Ghost is the soul of a dead person or animal who was not admitted to Heaven. If a soul that was not admitted is over eighteen, (or is considered an adult) they are sent to Hell. If they are under eighteen, (or not considered an adult) they are to spend their existence on earth, as a ghost.
The cause for human souls becoming ghosts varies, but ultimately, it comes down to a negative response to a Heaven request or a visiting.
- Human Blood-drinkers (those who still drunk human blood before they died, i.e did not make the decision to quit/was not in the process of quiting) are not permitted in Heaven, for that is cannibalism. Cannibalism is not okay.
- Deaths-by-Intentional Suicide can only result in a declined request to Heaven, as it is the ultimate sin.  Deaths that are a result from saving another are not considered Intentional Suicide.
- When a close friend or family member is grieving, souls that would otherwise be admitted to Heaven are allowed to return to earth (as a ghost) to guide that person/those people through the grieving process.
- When a close friend or family member contemplates suicide, souls that are living in Heaven may visit earth, and that person, until they are safe.
- Gengangers, spirits who were admitted to heaven but declined entry, choose to return to earth as ghosts.
False ghosts can be created by Grass Dwellers. All Grass Dwellers are able to create apparitions, and, with training, can conjure frightening and life-like beings that appear to actually have a sense of touch. For example, mastery of stage one for Jungle includes the conjuration of a night ghost (one that appears as a trick of light at nighttime). Stage two mastery for Savannah includes a conjuration of false Slenderman, and to master stage three, this Slenderman must be able to carry and use a body bag.