The Hakuyajuu (Spirit Beast) blade is the blade containing the powers of the Ancient Spirit Beast.
At one time, there was a world separete to ours that housed many large animals known as Spirit Beasts. When Myoken was defeated by Unagi Hyuga, the world was destroyed and only 2 of them survived. One of them was the Spirit Beast and the other was the Ancient Spirit Beast. The ancient one was known to be much stronger then the other one, for it was known as the leader of the World of the Spirit Beasts. These 2 later would battle for control of the World and the ancient one won out but became a blade, while the other one was sealed within a gate. The one who become a sword was the ancient one and was found all those thousand years later by Urugi and he made it his main weapon. The spirit and Urugi became close comrades, even when Urugi joined Akatsuki.
Appearance of Blade
It looks like an average katana with a dark blue hilt and guard along with a dark purple blade.