Quick couple of setting notes. First not ALL are evil, only a majority. Just saying. Also, not only men became changed. Animals and plants got hit with the magic too.
now for a random tidbit on the setting. Expect these as I think of them. Also, great story vulnus.
anyway
"The capital of Old Tenki was the city Tenki. It was a sprawling metropolis in the center of a lush valley. The rulers of the city had over time built up a frankly insane amount of defenses. There was even a wall of solid steel at one point, sadly scraped by looters some time long ago. It was layed out in a vaguely star shaped pattern, with the closer you were to the center being the richer/more important to the church you were. Outside the city proper was a sprawling shantytown, which served as the first line of defense, as its labyrinthine mass of alleyways and building slowed invaders down significantly. The second line was the outer wall, 4 meters thick, constructed of concrete and enchanted brickwork. Inside of this wall was where the majority of the population lived, as it was the more recent and larger segment. Behind another, smaller wall was the commercial districts, zoned off as such due to the relatively small space between the second and third wall. The next district was where the minor nobles built manors, as it was well defended and closer to the origin of the city than the larger outer districts. In the inner wall, the churches and government were housed. The emperor kept his palace here, which was lavishly staffed and furnished. This city was enveloped by the magic, and was unenterable for many years. Upon entering, the explorers found that the city had been warped, and its inhabitants maddened and twisted. A dark day when the former men and women of Tenki escaped."
-Parsius, scholar of the order of Venos, in his study "on the history of the city of Tenki" circa 1376