Shinju

The Shinju (神樹; Literally meaning "God Tree"), more commonly referred to as the Ten-Tails (十尾, Jūbi), is the primordial entity and the original tailed beast tied to the legend of the Sage of the Six Paths. Its chakra was divided into the nine tailed beasts and its body sealed into what would be the moon, by the Sage at the end of his life. Considered to be the progenitor of the world, its revival would herald the end of it. As of the most recent shinobi war, the beast was sealed within Obito Uchiha until the tailed beasts were extracted from Obito's body. The Beast was sealed within Cloud.

Background
Long ago before the founding of the hidden villages, during an era of endless wars between mankind, the Shinju existed as a tree that was revered as a deity which bore a fruit once every thousand years. Although it was forbidden to consume the Shinju's fruit, it was eaten by Princess Kaguya Ōtsutsuki who used the power it granted her to end the wars plaguing the lands. Some time after this, Kaguya gave birth to a son who became the first human born with chakra. Outraged by the theft of its power, the Shinju assumed its tailed beast form of what many christened as the "Ten-Tails". The Ten-Tails rampaged throughout the lands until Hagoromo managed to single-handedly defeat the beast and sealed it within himself. This act, along with many other great deeds throughout his lifetime, resulted in Hagoromo becoming revered as the "Sage of the Six Paths". However, knowing that his death would unleash the Ten-Tails back into the world to continue its rampage and reclaim the chakra that humanity now possesses, Hagoromo separated the monster's chakra from its body before using Chibaku Tensei to seal the husk in what would become the moon. From there, the Sage used his Creation of All Things ability to divide the chakra into the nine tailed beasts. Centuries later, the Rinnegan would once again manifest itself in one of Hagoromo's descendants: Madara Uchiha. With his new power, Madara summoned the empty vessel of the Ten-Tails back into the world and named it the Demonic Statue of the Outer Path. Joined by Obito Uchiha, who continued his work after his natural death, Madara devised a means to reunite the Demonic Statue and the tailed beasts back into their one original form so he could use the Ten-Tails to enact his life-long objective: the Eye of the Moon Plan (which Cloud have completed it).

Appearence
Silhouetted prior to its introduction in the story line, the Ten-Tails is a cyclops-like humanoid in appearance with a conch shell-like upper body with long, spiked-like protrusions on its back. Its unique red eye, taking up most of its head, has four concentric circles with nine tomoe in the three circles closest to the pupil. In a later appearance, the Ten-Tails' look was a bit more "crass". The spiky protrusions on its back were much higher, resembling a conch shell, and its tails were bushier. It appears to have a tan skin colour.

Personality
The Shinju is an impartial entity and was completely devoid of feelings or even ideals as it stayed impartial and almost ambivalent to the constant wars that were waged around it by mankind. But as the tree became the Ten-Tails, it was singular in its goal: to reclaim the power that had been taken from it and as Kurama noted, this form of singularity in its mindset made it impossible for those to sense it through such means such as involving detecting negative emotions or even chakra due to its vast power. Individuals in Sage Mode are best able to gain some sense of the beast's power, and even then it appears unmeasurable and overwhelming; Kurama likens the Ten-Tails to be an innate force of nature.

Abilities
As the original form of all nine tailed beasts, the Ten-Tails was said to possess massive and overwhelmingly foul chakra that is potent enough to bring total despair and destruction to the world. Not only is the Ten-Tails the source of all chakra, but also the progenitor of everything that exists in the world. It is a god that created countries and has the power to swallow oceans, split the land, and carry mountains. In addition, Kurama admitted that it alone wouldn't even stand a chance against the Ten-Tails, and stated that the Sage told them that its revival would result in the end of the world. A single swipe of its tail was can create a shockwave powerful enough to tear up the landscape around it.