Ten Tails: The Untold History.

It is regarded as the progenitor of chakra, and is tied to the legend of the sage of six paths and the birth of shinobi. It is the source of all chakra and the origin of the tailed beasts. It is also the catalyst for many events and conflicts that shaped the world of shinobi. Serving as a pivotal factor in the unending conflict. The tailed beasts were created by the sage of six paths a thousand years ago, born from the chakra of the ten tails.

The latter having eaten its chakra fruit and later merged with the god tree in a battle against her sons, hagoromo and hamura. It is a titanic, nightmarish, demonic deity of unfathomable power who laid ruin over the world in the beginning of time.