Ninjas are all about discipline. That's probably the reason why Kurai Kage has been an outcast for most of his life. He fights only with the worst intentions. He's been in several armies, but never lasts long. When the blood runs dry, he gets bored and moves on to serve another leader. His new boss is Yaoguai Wangzhou, the self-proclaimed Emperor of the Eastern Regions.
Kurai Kage was general of Yaoguai Wangzhou's forces. He was corrupted by Fayemalice alongside Wangzhou, as part of the conditions of their alliance.
Kurai Kage killed Kenrei when he was a bandit. Kenrei's spirit came to fight against him and Wangzhou when he learned that Kage was in a position of power.