Tailed Beasts

The tailed beasts (尾獣, bijū) are nine giant demons. They are differentiated by the number of tails they have, with each possessing a number from one to nine. The tailed beasts are large, living forms of chakra, sometimes referred to as "Chakra Monsters" (チャクラのバケモノ, Chakura no Bakemono),[1] giving them power that far outmatches most shinobi. However, this immense strength is tempered due to their bestial nature, which restricts them from being intelligent enough to use it effectively. When tailed beasts are sealed within humans, they are able to benefit from the knowledge of their hosts, giving them the ability to speak and better utilize their powers.

In the beginning of ninja history, centuries before the founding of the ninja villages, there existed one demon, the Ten-Tailed Beast, that plagued the world until the Sage of the Six Paths defeated and sealed the beast within himself, making him the first jinchūriki. However, knowing that his death would release the Ten-Tails back into the world, the Sage used his ability, the Creation of All Things (万物創造, Banbutsu Sōzō), to divide its chakra into the nine other tailed beasts, before using Chibaku Tensei to seal its body away in what would become the moon.