Death

After perishing, a person's soul exits their body and will generally remain around where they perished until they are visited by a mysterious entity. They go by many names: angel, reaper, judge, and many more, but their purpose is all the same in sending souls to the afterlife.
  If one lived a good or even neutral life, they are sent to an afterlife where they are permitted rest until they one day become reincarnated back into the living world. Those that lead evil lives, however, are sent to the Underworld, where their souls are cleansed of the evil they committed before they are reincarnated once more back into the realm as a new, pure being.
  However, these reapers are not perfect as they too have lives and faults just like the living. At times, it may take them a long time to reach a soul, causing them to linger as ghosts and other spectral entities, something may happen to the soul that traps and transforms them into Anima, or worse yet, they may be so tormented by their fate that they change into a monstrous entity as they try to deny their death and force their will back upon the world.
  Regardless, though, it is the duty of these reapers to see these souls sent to where they must go, so that they may be reborn anew later on.