Ten-Tailed Beast

The Ten-Tailed Beast is a gigantic Demon God of unfathomable power from the Naruto franchise, who presided over the world in the beginning of time. It is rumoured to be the progenitor of all life and the harbinger of doomsday.

The God-Tree
In the beginning, humanity was constantly at war with each other. There was no ninjutsu and therefore no ninja, due to the fact that all the mystical energy in the world resided in a divine tree. Once every thousand years, the tree would bear fruit. A woman consumed this fruit, gaining the powers of a goddess and putting an end to the conflict. The God-Tree was upset by this and transformed into the Ten-Tails, wreaking havoc across the land. The woman gave birth to a pair of sons who inherited all of her powers. One of these sons would grow up to become the Sage of the Six Paths.

The Sage of the Six Paths
The legend of the Sage of the Six Paths, the man who became the foundation to the fundamentals of ninjutsu, played a vital role in the series storyline. The combined might of the Sage and his brother was enough to counter the threat of the beast, successfully overpowering it. When the Ten Tails was defeated by the Sage, he sealed the monster within his body. However, as the seal he placed would fade upon his death, the Sage used his power to prevent the Beast's return by dividing its immense chakra into the nine Tailed Beasts with the monster's semi-lifeless body sealed away within the moon where it rotted over time.

Though separate with names of their own, the Tailed Beasts were all linked to each other. But in time, the Tailed Beasts parted ways and became legends in their own right. It was only by the actions of Hashirama Senju, a descendant of the Sage of the Six Paths, that the Tailed Beasts were all placed with captivity of various Ninja villages: Kurama the Nine Tails ended up with the Hidden Leaf Village, Matatabi the Two Tails and Gyuki the Eight Tails with the Kumogakure, Isobu the Three Tails and Saiken the Six Tails with the Village Hidden in Mist before the former escaped into the wild, Son Goku the Four-Tails and Kokuō the Five Tails with Iwakagure, Chomei the Seven Tails in Taigakure, and Shukaku the One-Tail in the Village Hidden in Sand.

Madara's Plot
But Hashirama's rival Madara Uchiha, another descendant of the Sage, took his rival's blood and used it to become a near-genetic match to the Sage. By the time he gained the Rinnegan as an old man, Madara summoned the Ten-Tails's body, the Demonic Statue of the Outer Path back into world to enact his Eye of the Moon Plan to reform the Ten Tails and become it new host to alter reality itself to suit his ends. But as he is near death, Madara conditioned Obito Uchiha as his successor to carry out his will through the Akatsuki to capture the Tailed Beasts and then revive Madara through Nagato.

Appearance
The Ten-Tailed Beast's appearance is fairly nebulous for the majority of the story. When Tobi first mentions its existence, the Ten-Tails is a humanoid silhouette with spikes erupting from its back and ten fox-like tails. Kurama's knowledge of the Ten-Tails shows the creature as looking slightly more bestial than what Tobi described, with a more jagged outline and an upper body that looks like a mountain with spiky protrusions. The only constants in all of the Ten-Tailed Beast's appearances is that it has a single eye that resembles both the Sharingan and the Rinnegan, as well as dwarfing the other 9 Tailed Beasts in size.

The Gedo Statue, which is later revealed to be the husk of the Ten-Tails, resembles a withered humanoid with sawed-off branches growing from its upper body, cuffs on its wrists and ankles, a gag in its mouth and 9 eyes. The eyes are initially empty orbs until the statue consumes a Tailed Beast, at which point a pupil appears in one of the eyes. When all nine Tailed Beasts are sealed within the statue, its eyes start weeping blood before undergoing its metamorphosis.

In its larval stage, the Ten-Tailed Beast has a bloated, veined body with a mouth like a cave opening filled with stalactites and stalagmites where its teeth and tongue should be. It has two arms and no legs, so it mainly moves around by dragging itself. The beast has a large spike on its back with smaller spikes growing from the main spike. Its tails are wrapped in several layers of carapace that unfurl as it undergoes its next metamorphosis. When Madara talks about the Ten-Tails, he always envisions it in this form.

In its second stage, the Ten-Tails has a skeletal body with two legs and one arm. Its tails now look like tubes ending in baby hands. The beast's head now has its eye on the left side of its head with its now smaller mouth on the right and an ear on the back. It also has horns on its head and under its eye.

In its third stage, the Ten-Tailed Beast gains a second arm, along with muscles and longer horns. It also possesses the ability to stretch its mouth open the length of its body and regurgitate a large flower that can shoot energy waves. If the beast was allowed to mature further, it would become bloated and grow spikes on the rest of its body, resembling the form it took when the Sage of Six Paths last encountered it.

After Obito becomes its Jinchuriki, he's able to turn the Ten-Tailed Beast into its Shinju form. As Shinju, the Ten-Tailed Beast transforms into a gigantic flower taller than any mountain with roots that resemble dragons. According to Madara, in the center of the flower is the beast's eye.

Revival
Though the actions of Naruto Uzumaki hampered much of the original plan, Madara was revived through Kabuto Yakushi during the Fourth Great Ninja War while Obito used the trace chakra of Gyuki and Kurama to begin the Gedo Statue's painful regeneration into an incomplete Ten Tails despite Naruto and Killer Bee's attempt to destroy it. Obito and Madara then jump onto the Ten-Tails and interface with the monster as they have it overwhelm the two Jinchuriki and Kakashi. Just as the Ten Tails is about to destroy them, the remainder of the Shinobi Alliance appears to help fight Madara and Obito. Naruto announces that their combined powers will end this war once and for all.

The various ninja all use their signature-jutsu to encase the Ten Tails, while Naruto and several others blind the monster before directing their assault on Obito and Madara. At that moment, the Ten Tails begins to transform into an even more bizarre form. Revealed to be its adult stage, the Ten-Tails begins firing Tailed Beast Balls from its mouth with a recoil from not adjusting to its form, destroying far-away villages and the allied ninja forces' base of operations. By that time, the Ten Tails begins to resist its masters' control before their ties are severed.

Now acting on its own will, the Ten Tails terraformed the area with various storms and earthquakes before gathering strength upon seeing images of the Tailed Beasts and the Sage of Six Paths around Naruto. When the revived Hokage appear and imprison the beast, Naruto, along with Sasuke, Sakura and the remainder of the Ninja Alliance, launch an assault on the Ten Tails. The Ten Tails is able to hold them back by spawning an army of monsters, but Naruto and Sasuke manage to get through and cause it some damage. Just when it seems like the Ten Tails' defeat might be imminent, Obito appears on its head and manages to seal it inside himself, becoming its host.

Obito's Ascent
Despite outclassing every ninja who faces him, Obito is backed into a corner by the combined efforts of Naruto along with the Second and Fourth Hokages. Obito then unleashes the Ten-Tails, which undergoes one more metamorphosis, this time becoming the God-Tree. The God-Tree then sucks dry the chakra of several ninja as it grows to its full size. According to Madara, once the flower on the God-Tree blooms, humanity will be cast into a world of illusion with no end.

After a combining their efforts, Naruto, Sasuke, Kurama and their allies are able to strike Obito, which causes the Ten-Tails to split back into the 7 tailed beasts. Naruto and his allies then extract the beasts from Obito's soul. The God-Tree remains.

Madara's Victory
After Obito's defeat, Madara forces him to resurrect himself. Now fully alive, Madara extracts the Demonic Statue of the Outer Path from Obito and uses it to ensnare all nine Tailed Beasts. They're all dragged in and used to once again bring back the Ten-Tailed Beast. Madara then seals the beast inside himself and becomes the most powerful being on Earth. When Naruto and Sasuke gain the powers of the Sage of Six Paths, they're able to overpower Madara. The God-Tree telepathically tells Madara to absorb it.