That method did not exist, but it could easily be imagined how ordinary people could be used as human batteries to constantly keep around to siphon Life Energy from them.
There did seem to be some kind of fundamental law involved when it came to taking away the Life Energy of another, which may have had something to do with that Life Energy being linked to them.
That Life Energy could be leaked out of humans and transform into a Spirit or Evil Spirit, but once it took on a whole new life, that embodiment of Life Energy solely belonged to it for as long as it remained living.
It was the same for the Life Energy that remained within an ordinary human, a Watcher and a Balancer when it came to who the Life Energy belonged to.
Ordinary humans were the exception since they did not know how to stop that Life Energy from leaking away and escaping their bodies, so it became separated from them, but the Life Energy that remained tied to them still had a connection to them.
