Takatukahane

Xuan Wu (Eng: Black Warrior), one of the four important symbols of Chinese Constellation, is also a deity in Taoism. Xuan Wu was told that in order to fully achieved divinity and become a god, he must purge himself from all his past sins and little niggly bad habits and naughty thoughts by washing his stomach and intestines in the river. I have no idea how but he washed them and painted the entire river black. (Meanwhile, listening to Rolling Stones, Paint it Black is highly recommended.)

Xuan Wu purged himself 100% of his sins as he wished. However, the black waters in the river became a tortoise and snake and started to terrorize the people in the country like a little demon mafia gang, causing people to fear, disturb, and terrorize as a hobby. When Xuan Wu found out this and knocked sense into them. They also regretted what they had done, kissed his hand as a sign of subservience (Now you may listen to the Godfather theme song)

In another version of the story, all the evilness in Xuan Wu oozed out into a black sloppy mess on the floor which turned into a black tortoise. This Mysterious Black Warrior Tortoise flew into the sky and became the guardian of the North. The tortoise depicted with a serpent entangled over its body represents the winter season. Since it lives in the ocean, its element is water. The Black Warrior is identified with wisdom, happiness, and longevity.

• Xuan Wu, Godchecker.com
• Çin Mitolojisinde Dört Önemli Sembol, Fwmail.com
• Black Tortoise, Wikipedia