Xuan Wu was one of the Three Human Sovereigns in the Spirit Realm. He ruled over the Black Tortoise Mirror. The Hegemon's Black Tortoise City was constructed on the back of a tremendous Lightning Turtle known as Can Ling. It was a huge city that could slowly move through the sea.
Due to appearance of the Profound Heavenly Spiritslash Sword, many races started preparation for war to compete for the treasure. The possesion of it could attract a True Spirit-grade existence and cause it to protect their clan and turn it into the strongest tribe in the spirit realm. These True Spirit-grade existences are superior to Immortals from the True Immortal Realm.
Sovereigns Xuan Wu and Tian Miao have been assigned to get rid off all of settlements of foreign races near Deep Heaven City. When they entered the Primordial World, they encountered a Lightning Turtle. Tian Miao wanted some of it's parts to refine a Ten-Headed Giant Devil. And Xuan Wu wanted it's lighting orbs to elongate a lifespan of his own Lightning Turtle.