“It is a sight to behold: like a giant spider web - dozens upon dozens of rope bridges and lines are strung between the hills of the district. And the people. They move along these slender swaying lines as if they were walking down a boulevard.”, The Journal of Mathius Redcap
All spell casters gain their abilities through a form of demon possession. So in order to gain magical abilites, PCs must track down and trap demons. Of course there are some pretty powerful demons, if the demon is stronger than the PC, the PC could find themselves subjugated to the Demon's will.