Mortal Races: Revenants
When a person dies, their soul travels to Purgatorio, to be purified and eventually reborn; or else to Paradiso or the Inferno, if they were particularly virtuous or sinful. Sometimes, however, a soul lingers for a time. Ghosts are created when someone dies with extreme emotion and some unfinished business. Rarer still are the times when the soul of the dead returns to its own body, to finish its dying wish itself. These revenants have effectively reincarnated in their own dead body as a result of their great willpower and overpowering emotions. If their will is disrupted, or their emotions settle, then their soul continues on its journey, which usually happens when they have resolved their final task. It becomes harder and harder for a soul to sustain itself in its body over time, which can also lead to the revenant moving on.