Positive emotions were not so much of a problem as it was the negative emotions that could be the spark for such a thing.
If a Balancer or Watcher died of natural causes or died before their time, then that would usually be the time that a Vengeful Spirit would be more likely to appear.
It would be the result of those kinds of negative emotions and thoughts that would be present in their final moments before their death.
Those very things would become the very catalyst for such a Vengeful Spirit to be born after their life came to an end.
If they did not die due to something of the supernatural world, like an attack from another Balancer or dying in battle to a Spirit or Evil Spirit, then there existed a possibility that they could come back as a Vengeful Spirit.
It would have to be a direct attack that was in the form of Life Energy; then their body and soul would not be exorcised of such things, which could manifest in such a way.
