Fate Freelance Inc.
Each of the planes resonates on a slightly different metaphysical frequency, with each carrying its own specific variety of Taint. To the natural residents of the plane, this is nothing to worry about, but to visitors, it can be something very serious. Most residents of The City are not aware of what taint is or how it works, let alone what each realm’s specific taint is. The City was specifically constructed to be free from any Taint, and Taint from other realms cannot take hold due to the Working which is tied to the Shrines present throughout the city.
Taint is the number one reason full scale war has not broken out between various planes over the centuries. Taint affects everything from how a given piece of gear will function to mindset and physical structures of things. Some realms have taint so severe they are extremely dangerous to even enter. There are a number of technological, etherilogical, and magical ways to protect one’s self and personal possessions from Taint. These ‘rituals’ should be followed to the letter while visiting another realm. While one may believe that using such protections should allow someone to bring an army through to a more ‘primitive’ plane with its ‘superior technological resources’, they would be quite wrong. The larger amount of non-Tainted items and people together, the higher the rate of taint to match the paradigm of the realm they are in. No race is currently totally immune to taint, and non-tainted humans are the most susceptible to realm taint.
This is not to say that covert teams have not infiltrated into realms to assassinate, commit sabotage, or cause other problems for their rivals. This is something that keeps the leadership and spymasters of each realm awake at night, and very much employed, in the case of the spymasters.