Long before the founding of the hidden villages, during an era of endless wars between mankind, the God Tree, a tree revered as a deity, bore a chakra fruit once every thousand years. Although it was forbidden to consume the God Tree'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 two sons who became the first people born with chakra. Later, deciding that her children's chakra was rightfully hers, Kaguya combined with the God Tree to become an entity known as the Ten-Tails, which ravaged the land in an attempt to obtain said chakra. However, because Kaguya's true motives were not realised, it was instead believed that the God Tree itself had taken on the form of a monster in an attempt to regain the chakra that Kaguya had stolen. In the final battle between the Ten-Tails and Kaguya's sons, Hagoromo and Hamura, they managed to defeat the beast and sealed it within Hagoromo, making him the first jinchūriki. This act, along with many other great deeds throughout his lifetime, resulted in Hagoromo becoming revered as the "Sage of Six Paths". However, knowing that his death would unleash the Ten-Tails back into the world to continue its rampage and reclaim the chakra he had spread among humanity, Hagoromo separated the monster's chakra from its body and used his Creation of All Things Technique to create the nine tailed beasts. Hagoromo then used Chibaku Tensei to seal the Ten-Tails' husk in what would become the moon. Unbeknownst to the brothers, Kaguya had created Black Zetsu prior to her sealing in order to facilitate her revival. To this end, it spent centuries attempting to unite the chakra of Hagormo's sons, Indra and Asura, in order to cause one of their reincarnations to awaken the Rinnegan. Eventually, thanks to Black Zetsu's machinations, 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 death, Madara devised a means to reunite the Demonic Statue and the tailed beasts back into their original form so he could use the Ten-Tails to enact his lifelong ambition: the Eye of the Moon Plan.
According to Kurama, the Ten-Tails cannot be sensed through such means as detecting negative emotions as it has no feelings or ideals of its own. Despite this, when it sensed the presence of the tailed beasts' chakra inside Naruto Uzumaki and was reminded of Hagoromo, it reacted by gathering chakra and strengthening itself. It was believed that the Ten-Tails was an incarnation of the God Tree with the singular goal of regathering the chakra that Kaguya had stolen from it but in actuality, it was following Kaguya's will to reclaim all chakra for herself. The Ten-Tails is brown in colour and titanic in size; one of its hands is larger than any of the tailed beasts. While the beast possess multiple forms, common attributes include a single eye, which takes up most of its head, and spiky protrusions growing out of its back in a shape reminiscent of a conch shell. When it was initially revived in an incomplete form, the Ten-Tails possessed a grotesque bulb-like body with long arms and clawed hands, but no visible hind legs, as well as a wide mouth with multiple rows of pointed teeth and a single spike on its chin. Dark veins similar to those of a plant ran along its body, and the endings of its tails resembled leaf buds, which unfurled as it began entering its second form. In its next form, the Ten-Tails took on the shape of an emaciated humanoid with elongated limbs and a twisting neck. It now possessed visible legs, which it used along with its right arm to stand, as its left arm was missing from the elbow down. The beast's head was altered greatly, as its eye remained on the front of its head, it grew a single ear on the right side, and its mouth which now contained straight teeth and bore a grin moved to the left side, with a single triangular nostril appearing above it. Several horns formed on various parts on its head: two above each side of its face, two beneath its eye, and another below its ear. As it transformed, the bud-like attachments on its tails detached, revealing extendable tails which ended in humanoid hands. After further maturing, the Ten-Tails' body became less emaciated, it grew a complete left arm, and it began standing on its hind legs. It later gained an even more muscular appearance and the horns on top of its head grew in size. When Hagoromo and Hamura encountered the Ten-Tails, it strongly resembled this form, albeit with a bloated appearance and additional spikes on its body. After becoming the Ten-Tails' jinchūriki, Obito expelled a construct of the Ten-Tails from his body, which then split open to reveal a gigantic tree, much like the original God Tree. This tree form, which completely dwarfed the Ten-Tails in size, possessed a tall, straight trunk with a single purple bud situated on top, inside of which was the Ten-Tails' eye. This tree form was initially stated to be the God Tree, but it was later referred to as the Ten-Tails. When Kaguya Ōtsutsuki lost control over the tailed beast chakra inside her after being hit by Naruto Uzumaki's attack, she unwillingly transformed into a non-humanoid Ten-Tails that manifested as a bloated, white, rabbit-like form, with the heads of the nine tailed beasts growing from various points on its body. This chakra-based form of the Ten-Tails retained Kaguya's Rinne Sharingan on its forehead as well as ten tails ending in hands.
