Impurity

An Impurity (or "impurities", also known as "kegare" in the anime) is the name for monsters that reside in a world named Magano, but at times break into the human world. Those who fight the Impurities are called Exorcists.

Both Magano and Impurities are said to have been born from the depths of people's sins and karma.

Impurities vary on appearance and size, but usually share some common traits like dark skin and a net/number sign on their chest/stomach.