Zero-Tails

The is a dark leech-like spirit with a noh mask sealed within Amaru.

Zero-Tails is a spirit which grew out of the dark thoughts and feelings of the downtrodden. Though it bears a numerical tail name, it is not a true Tailed Beast. It feeds on any negative emotions within ones heart and allows the spirit to create dark chakra. When anyone near the Zero-Tails is emotionally unstable, it will inhabit their body and take them over. The remnants of the Sky Country used the Zero-Tails to discretely create enough dark chakra to power their ultimate weapon, "Ancor Vantian." This dark chakra was also personally used by Shinnō, the man who orchestrated the revivial of the Sky ninja forces.