Guren

Guren is a unique Azafuse in the series, given his oily black fur. He is a most evil yokai, cunning, dangerous, and sadistically bloodthirsty. As a human 1700 years ago, he was a cruel mercenary known as Sokuei, who was not only a wielder of the Beast Spear, but one who killed yokai and humans for pleasure. Sokuei's wicked and bloodthirsty nature easily allowed the Beast Spear to transform him into an azafuse, but because of his evil soul, his fur was black instead of gold or orange like most azafuse. Forgetting his human self, he took on the name Guren. As most Azafuse eventually did, Guren turned to stone for the purpose of awaiting the final battle with Hakumen no mono. However, Guren only wanted to kill, and his bloodthirsty nature attracted an avatar of Hakumen, possibly Towako. The avatar was able to converse with him in his dormant state and offered him power, and the endless chance to kill as much as he wants, in exchange for his loyalty. Guren obliged and eventually broke free. He first attacked the village that had always been in his sight when he was stone. There he killed a woman and her daughter and scarred the husband when he came home, permanently damaging the man's right eye. Guren eventually met this man again, who had since become a Chinese Excorsist under the Alias Hyou. Hyou and Guren had a final battle that ended in a draw when Hyou tricked Guren into destroying himself while the excorist died of his wounds. (Source: Ushio to Tora Wikia)