From the Inside Flap
In each city, high and protected in the city's Watchtower, lives the Demon Lord of the dimension. And so long as that demon remains on Earth, his curse will reign over the circle where he resides. In an attempt to reverse the damage, thirteen of the strongest angels were sent to Earth to defeat the Demon Lords. However, their sacrifice came at a price: they would have to take on the curse of the circle they were sent to, and would be damned to Earth until the curse was lifted.
These are the stories of the Cursed Angel Watchtowers.