Gheist

Monsters born from the souls of prisoners who have died in jail. Innocent people who have been wrongly jailed and died in regret are said to roam the world as gheists. The souls that have been imprisoned in the dark cells are still bound there, even after becoming reapers. Gheists are the cause of a troublesome phenomena where they shiver their bodies in an attempt to escape the darkness, which triggers a deafening boom that can blow things around it away.