Girl-Ghost!

Aaron and Henna stray into zombie-land, a port-town and end up with another wizard trying to cure a girl-ghost of an unwanted boyfriend.

All depts are paid, eventually.
You train and develop.
Develop, self-improvement, problem-solving.
But if you stray into areas you weren't designed for; or for greed vanity or power
for low goals, low methods and low results, things go bad.

It isn't that demons take over you... it just that the low development attracts low people to you.