World of Naruto - Phenomena - Tailed Beasts

The Tailed Beasts (尾獣, Bijū?) are nine giant concentrations of Chakra that serve to drive the plot of the Naruto series. They were all originally part of a single entity of unknown origin called the Ten-Tails (十尾, Jūbi?), whose power far outmatched most ninja and was said to had created all life on the world. As the legends reveal, the Sage of the Six Paths sealed the Ten-Tails inside his body to prevent the monster from terrorizing the world. But as his death would release the Ten-Tails back into the world, the Sage separated the Ten-Tails' chakra from its body and scattered it into the four winds as the Tailed Beasts before sealing the body away in what would become the moon. Though referred to by the number of their tails, from one to nine, the Sage gave them proper names as he regarded them with respect: Shukaku (守鶴?) the crazed one-tailed tanuki; Matatabi (又旅?) the polite two-tailed cat; Isobu (磯撫?) the shy three-tailed turtle; Son Gokū (孫悟空?) the prideful four-tailed ape; Kokuō (穆王?) the reserved five-tailed dolphin-horse; Saiken (犀犬?) the boastful six-tailed slug; Chōmei (重明?) the cheery seven-tailed rhinoceros beetle; Gyūki (牛鬼?) the berseker eight-tailed octopus-ox; and Kurama (九喇嘛?) the cynical nine-tailed fox. The beasts are told by the Sage of a certain person and that one day they would be joined back to their original form while understanding true power.

Each Tailed Beast is differentiated by the number of tails they have, an ideal Tailed Beast embraces though their immense strength is tempered due to their bestial nature. However, wanting to use the powers of the Tailed Beasts for their own, many of the ninja villages resorted to having the beasts sealed within Jinchuriki: Shukaku used by the ninja of Sunagakure; Matatabi and Gyūki by Kumogakure; Isobu originally owned by Kirigakure, alongside Saiken, before it escaped; Son Gokū and Kokuō by Iwagakure; and Chōmei by Takigakure. With the exception of Gyūki, though they benefitted from the knowledge of their hosts and better utilize their powers, the other Tailed Beasts despised the humans for their actions and being seen by them as nothing more than tools. Only Kurama evaded capture until the founding of Konoha, in which Madara Uchiha controlled it during his battle with Hashirama Senju and was sealed within Hashirama's wife Mito Uzumaki, eventually winding up to Naruto Uzumaki.

The Akatsuki, a criminal organization that becomes one of the primary antagonists of the series, spends much of their screen time trying to capture the nine beasts or their hosts. Once captured, the Akatsuki's members seal the beasts away within the Demonic Statue of the Outer Path, the Ten-Tail's body. Though their figurehead leader, Nagato believed the Akatsuki's goal is to use the beasts in the creation of a weapon capable of destroying an entire country to enforce peace, the organization was created under Madara through his apprentice Obito Uchiha, under the guise of Tobi, to reform the Ten-Tails and become its Jinchuriki to subjugate the Ninja World. Eventually, only Kurama and Gyūki remain to be captured after the five Kage's refusal to hand Naruto and Killer Bee to Obito, leading to the Fourth Great Ninja War. During the war, Obito reanimates the former Jinchuriki as his new Six Paths of Pain and seals the Tailed Beasts back within them in an attempt to capture Naruto and Killer Bee, though Naruto's determination to save the Tailed Beasts surprises and amazes them as Kurama realizes that he must be the person that the Sage told them long ago. However, knowing that he only has little time yet, he decides to begin the Ten-Tail's incomplete resurrection, using only the seven Tailed Beasts, Gyūki's tentacle, and parts of Kurama's chakra stored in the Gold and Silver Brothers (who were sealed in the Kohaku no Jōhei and Benihisago). As the Ten-Tails still need time to regenerate fully, Obito ensures no one would interfere while he and the reanimated Madara Uchiha attempt to fully add Kurama and Gyūki into it.