Ten-Tailed Beast

Ten-Tailed Beast

The Ten-Tailed Beast  is the original, primordial demon of the Naruto universe. All nine of the tailed beasts are but portions of chakra divided from the Ten-Tails. Madara Uchiha's ultimate goal, the Moon's Eye Plan, is to capture and merge all nine of the tailed beasts back into the Ten-Tails, and become its host to cast the reflection of his Sharingan on the moon, casting a genjutsu known as the Infinite Tsukuyomi which will put the entire world under his control.

Background:

Centuries before the founding of the hidden villages, the Sage of the Six Paths saved the world from the Ten-Tails. He managed to subdue the beast and sealed its chakra within his own body, becoming the first jinchūriki.However, this offered merely a temporary solution to the menace; in the event of his death, the seal would dissolve and the Ten-Tailed Beast would once again be unleashed upon the world. Knowing this, the Sage devoted the remainder of his life to searching for a more permanent solution. Ultimately, the Sage succeeded by dividing up the chakra of the Ten-Tails into the nine monstrous entities that would later become known as "tailed beasts" and scattering them throughout the world. As a final precaution the Sage, using his Chibaku Tensei jutsu, entombed the physical remains of the Ten-Tails within a colossal stone prison and hurled it into the heavens, creating the moon.

Appearance:

So far, the Ten-Tails has only been seen once, in silhouette, but the form of its body seemed to be closest to that of the Nine-Tailed Demon Fox's body. Also, it appeared to have only one eye, which had four Rinnegan-like concentric circles, with nine Sharingan-like tomoe in the three circles closest to the pupil.

Abilities:

As the fusion of all nine tailed beasts, the Ten-Tails is said to possess massive and overwhelmingly foul chakra that is potent enough to bring total despair and destruction to the world. The astonishing feat of not only successfully sealing the Ten-Tails, but also suppressing it, made the Sage a god-like hero throughout the shinobi world.

Nine-Tailed Demon Fox

The Nine-Tailed Demon Fox (九尾の妖狐, Kyūbi no Yōko) is the most powerful out of all nine of the tailed beasts; a single swipe from just one of its nine tails can raise tsunamis and flatten mountains. After the Nine-Tails attacked Konohagakure, Minato Namikaze, the Fourth Hokage, sacrificed his own life by sealing it within his newborn son, Naruto Uzumaki.

Background:

The Nine-Tails first came into being in the waning days of the Sage of the Six Paths' life; to prevent its resurgence, the Sage split up the chakra of the Ten-Tailed Beast into nine separate, monstrous constructs of living chakra, which would become known as the tailed beasts. Out of all the nine tailed beasts, the Nine-Tails is the most powerful and its form is also the closest to the form of the Ten-Tails. Over the centuries, the Nine-Tails gained a reputation as an age-old natural disaster, appearing at random to attack areas where human malice has collected and festered.
Many decades ago, when Madara Uchiha defected from Konoha, he used his Mangekyo Sharingan to take control of the Nine-Tails, and used it to help him fight against Hashirama Senju, the First Hokage, to exact his revenge. The battle was so great that it tore the earth apart and created the Valley of the End. Despite being in control of the Nine-Tails' power, Madara was defeated.
Many years later, the Nine-Tails attacked Konoha. Madara denied that he had summoned it to destroy the village and claimed that the Nine-Tails' attack had been a "natural occurrence". During the attack, the Nine-Tails decimated the shinobi that tried to repel it. Minato, riding atop Gamabunta, was able to defeat the Nine-Tails by sealing it within Naruto, which freed it from Madara's control.
In the anime, it was revealed that the Nine-Tails had left behind large amounts of its chakra during the attack. Kazuma collected and sealed the chakra within his own son, Sora, hoping to make use of its power for his own agenda.

Personality:

The Nine-Tails is a giant, malevolent fox demon of mass destruction. It is also intelligent, and has a sadistic and sarcastic personality. However, it does have a distinct sense of honor and pride, and possesses a loathing respect for Naruto and Minato.
At first, the Nine-Tails relished the thought of killing Naruto, but it soon realized that it shares the same fate as Naruto as long as it is sealed within him; so it has no choice but to cooperate with Naruto or it will die. It will go to great lengths to preserve its own life, as shown when it forces its chakra into Naruto whenever his life is in danger. Later in Part II, the Nine-Tails became angry and contemptuous at Naruto when he rejected its chakra, although this was merely the rage of missing the opportunity to usurp control over Naruto's mind and body, which would have weakened the seal. However, it will back down if Naruto threatens to harm or kill himself.

The Nine-Tails has a deep hatred for the Uchiha clan and their Sharingan, likely because of the many times Madara manipulated it in the past. It even remarked that Sasuke Uchiha is a lot like Madara because of his power of the Sharingan. According to the third Naruto Databook, the Nine-Tails is the only one who knows the truth about the Uchiha clan and about Naruto. However, it appears that it has no intention of telling what it knows.

Part I:

Naruto was not made aware of the Nine-Tails' presence within him until twelve years after its sealing. He first made use of its chakra during his battle with Haku. Believing Haku to have killed Sasuke, Naruto gave into his anger and entered his initial jinchūriki form in order to defeat Haku. He didn't realize that this was the Nine-Tails' chakra until he was later taught to take advantage of it by Jiraiya. To force Naruto to call upon the Nine-Tails' chakra, thus enabling him to use the Summoning Technique, Jiraiya threw Naruto off of a cliff. To save himself, Naruto entered his subconscious and met with the Nine-Tails for the first time. He demanded some of its chakra as "rent" in order to save them both, and the intrigued Nine-Tails complied, allowing Naruto to summon Gamabunta.

Naruto took advantage of the Nine-Tails again during his fights with Neji Hyūga and Gaara, requesting some of its chakra to help him with the battles. Later, when Kabuto Yakushi severed Naruto's heart muscles and the neighboring chakra system, the Nine-Tails was unable to heal the damage. It, like Naruto, had a near death experience, something it was slow to recognize. Naruto, and, through him, the Nine-Tails, were saved by Tsunade. During his battle with Sasuke at the Valley of the End, the Nine-Tails gave Naruto enough chakra to attain the one-tailed transformation, something the Nine-Tails indicated that he should be grateful for.

Part II:

During the timeskip, Jiraiya weakened the Nine-Tails' seal with the key in order to give Naruto more access to its chakra. This had the side effect of allowing Naruto to achieve tailed transformations with little provocation. When the three-tailed transformation was proven insufficient in a fight with Orochimaru, Naruto gave into the Nine-Tails and entered his four-tailed transformation. The Nine-Tails gained control of his senses and began to attack all around him, including both Orochimaru and Sakura Haruno. After its influence was suppressed by Yamato, he told Naruto how the four-tailed form had caused him to attack Sakura, someone that he cares about. Naruto resolved not to use the Nine-Tails' power again.
Soon afterwards, when Naruto met Sasuke again for the first time in years, the Nine-Tails tried to offer Naruto some of its strength. He refused, but before it could put up much of a fight, Sasuke appeared within Naruto's subconscious. Surprised, the Nine-Tails commented that Sasuke's chakra is more ominous than its own, and that he is just like Madara Uchiha. Sasuke forced the Nine-Tails back into its cage, but before it was completely suppressed, the Nine-Tails warned Sasuke not to kill Naruto, telling him that he would only live to regret it. It saw little activity after that, surfacing within some of Naruto's shadow clones that had grown frustrated with the wind element training. In the anime, the Nine-Tails reacted to its chakra stored within Sora. Naruto was able to keep the Nine-Tails from taking control of his body, but it managed to take back all of its chakra from Sora.
Later, when Naruto tried to learn senjutsu, the Nine-Tails prevented Fukasaku from fusing with Naruto, wanting Naruto to use its chakra instead of Sage chakra. It was given an opportunity to appear during Naruto's battle with Pain. After Pain appeared to have killed Hinata Hyūga, Naruto slipped into his six-tailed transformation, which the Nine-Tails used to its advantage by destroying the First Hokage's Necklace. When Naruto was captured by Pain's Chibaku Tensei technique, the Nine-Tails tempted Naruto to give his heart to it so that it could destroy everything that was causing Naruto pain, thus distorting the seal to the point where the eight-tailed transformation was released. Before it could convince him to completely remove the seal, however, the spirit of Minato appeared in Naruto's subconscious to stop him. Enraged, the Nine-Tails tried its best to kill Minato for revenge, but Minato ignored it, soon afterwards restoring the seal to its original strength. Once Pain was defeated, Naruto confronted Pain's base mind, Nagato, and was able to simultaneously use Sage chakra and the Nine-Tails' chakra, combining the two different pupil appearances.

Activity inside Naruto: As the Nine-Tails' jinchūriki, Naruto has accelerated healing, unrivalled stamina and speed, immense strength, and access to its massive chakra reserves. The Nine-Tails' chakra allows Naruto to perform his signature jutsu, Shadow Clone Technique, seemingly without limit. He is even able to summon Gamabunta, a feat that is normally Kage-level as the technique requires an amount of chakra proportionate to the size of the summoned creature. Although the Nine-Tails' chakra naturally mixes with Naruto's own, Naruto can forcefully tap into its chakra reserves. After training with Jiraiya, he learned to request some of the Nine-Tails' chakra for his own use. Alternatively, and what has become the more common method over time, he can give into his anger or frustration, allowing the Nine-Tails to force its influence upon him. Depending on how much of its chakra he gains, Naruto can lose control of his senses, devolving into an animal that attacks anything within reach, as well as damaging his body with the Nine-Tails' chakra, slowly shortening his lifespan. For these reasons, Naruto learned to exercise more control over the Nine-Tails' chakra. A number of methods have been devised to break the Nine-Tails' influence over Naruto: Yamato can use the Hokage-style Sixty-year-old Technique - Kakuan Entering Society with Bliss-bringing Hands, which was facilitated by the necklace Naruto wore before it's destruction; a Chakra-Suppressing Seal can be applied to Naruto's body; or an Uchiha with a mature enough Sharingan can enter Naruto's subconscious and force the Nine-Tails to recede. The most effective of measures, however, is Naruto simply limiting his use of the Nine-Tails' chakra and not allowing his anger to get the better of him.