Tailed Beast

The are nine giant demons in Naruto. Those seen thus far are slightly larger than Gamabunta, who is over 100 meters tall. The tailed beasts each have a different number of tails, and each is a different type of creature. Compared to humans, tailed beasts possess a massive amount of chakra, described in the series as the "ultimate chakra". Shukaku seems to possess a chakra level several times that of any human, while the nine-tailed fox's chakra is practically limitless. Despite their unrivaled strength and power, not all of the tailed beasts are able to use it as effectively. The three-tailed beast, for instance, did not possess the intellect to control its own strength, making it weaker.

Those within whom a tailed beast has been sealed at birth are called, and grow up to exhibit extraordinary powers. In some instances, they are actually stronger than the tailed beast they possess. This is because they have the knowledge to control the tailed beast's strength effectively, whereas an unsealed tailed beast may lack the necessary intelligence to do so. The host also tends to have some sort of physical characteristic akin to the tailed beast sealed within them (Naruto's whisker-marks, the rings around Gaara's eyes, and Yugito's slanted eyes). Naruto takes the word "host" offensively, regarding it as a dehumanizing term. According to Akatsuki members, those who host such creatures are typically lonely people who loathe humanity, and so far this has proven to be true (at least at first). When the first two were captured, no one from their villages cared that they were taken or lifted a finger to help; in fact, they were thankful to be rid of them. It is known that the death of a host will result in the death of the tailed beast within, and the hosts seen thus far sometimes exhibit involuntary defensive powers. Likewise, the removal of the tailed beast results in the death of its host.

During the Great Shinobi Wars, each country's Hidden Village tried to make use of the tailed beasts for military purposes, and competed for them. However, no one was ever able to truly bring the tailed beasts under control. The practice of sealing tailed beasts within humans to harness their powers proved the only effective method of harnessing the awesome powers of the beasts.

Akatsuki is currently collecting the nine tailed beasts. They capture the hosts and take them to a secret location where a three day long jutsu is performed to draw out the tailed beast from the host. They possess six tailed beasts: the Shukaku, the two-tailed demon cat, the three-tailed beast, and three other unknown beasts. Every one has been extracted and sealed.

One-Tailed Shukaku

 * Name: or
 * Creature type: Tanuki (raccoon-dog, native only to Japan and other Asian countries)
 * Host: None, formerly Gaara
 * Unique traits: Able to spit concentrated balls of wind mixed with chakra
 * Status: Captured, extracted, and sealed by Akatsuki

Shukaku is said to be the corrupted spirit of a Sand monk turned demon. He was originally sealed inside a teakettle and then placed inside his first host. He was sealed inside Gaara by Chiyo on the orders of Gaara's father, the Fourth Kazekage, using Gaara's mother as the sacrifice. Shukaku had two other hosts before Gaara, both of whom died when Shukaku was extracted from them. Shukaku is intelligent but also incoherent, giving him the demeanor of a drunkard. Shukaku itself can translate to "drunk" in Japanese. Like other tailed beasts, its innate rage and bloodlust influence its behavior, and it relishes in the opportunity to kill anyone in sight.

As a host of Shukaku, Gaara has the ability to move and levitate sand at will, and is protected at all times by the Shield of Sand, regardless of his will (even self-inflicted injuries are prevented by the sand). He also suffers from lifelong insomnia, a side effect of being Shukaku's host. Should he fall asleep, Shukaku would eat away his personality.

When angry or particularly bloodthirsty, Gaara begins to transform into a human-sized version of the Shukaku by layering sand over his body. The sand takes on the appearance of the Shukaku, and enhances his abilities greatly. While in this form, Gaara gains immense strength, endurance, and the ability to use Sand Shuriken. He can also stretch his sand limbs as he does with his regular sand, the primary difference being that his limbs remain just as strong as when they are retracted. This transformation seems to occur very slowly, as Gaara attempted to assume this form twice and was foiled both times. In the first instance, Sasuke injured him during an attempted transformation in the Chunin exam. The latter, which Gaara nearly completes, is ruined by Naruto during their battle in the forest. Gaara has only been able to reach a point at which all but his legs have been covered in sand.

In dire situations, Gaara can create a life-sized replica of Shukaku from sand. Unlike his human-sized version, this replica can be created almost instantly. Gaara controls the replica from within, remaining safe from enemy attacks. Despite being made of sand, Gaara seems to be unable to regenerate any damage caused to the replica. While in this form, Gaara can also release Shukaku's spirit, allowing the demon to use his full power. To do this, Gaara must emerge from within the replica, settling on the top of its head, and force sleep upon himself. Once released, Shukaku can attack with his signature ability, Wind Release: Drilling Air Bullet. Because Gaara protrudes from the top of Shukaku's head, he can be awoken, thus suppressing Shukaku's spirit once more.

During the Rescue Gaara arc, Shukaku was forcefully extracted from Gaara by Akatsuki, thus killing him. Fortunately for Gaara, he was resurrected through a combination of Chiyo's life-transferring technique and Naruto's chakra. Gaara's ability to control sand still appears to be intact, though to what degree remains unclear.

Trivia
 * Shukaku is sometimes mistaken for a badger, raccoon or a panda.
 * Tanuki, like kitsune, are magical creatures in Japanese folklore, and the two often appear as rivals.
 * There is a Japanese tale about a priest and a Tanuki sealed in a teakettle, called Bunbuku Chagama.

Two-Tailed Demon Cat

 * Name:
 * Creature type: Nekomata (magical, two-tailed cat)
 * Host: None, formerly Yugito Nii
 * Unique traits: Fire-breathing
 * Status: Captured, extracted, and sealed by Akatsuki

The two-tailed demon cat is a fire-breathing, flaming cat from the Land of Lightning. Its host is Yugito of Kumogakure, who was captured by the Akatsuki members Hidan and Kakuzu shortly after her introduction. Despite luring her two pursuers into a closed space, sealing the exits, and transforming herself into the demon cat, Yugito was overpowered and rendered unconscious (as well as pinned to a wall by a kunai through her hands) by the two Akatsuki members. Zetsu later arrives to take her off their hands. In chapter 331, Akatsuki begins extracting the beast from Yugito, and finishes in chapter 332.

Trivia
 * Although the two-tailed demon is depicted as a Nekomata, it doesn't seem to exhibit the same abilities as the legendary creature. The nekomata of folklore was said to animate and control the dead, while this nekomata has fire-based abilities. However, this is an indirect reference to a Japanese belief that spirits of the dead manifested as airborne flames, similar to will-o-wisps.

Three Tails

 * Name:
 * Creature type: unknown (Turtle-like creature)
 * Host: None
 * Unique traits: Unknown
 * Status: Captured and sealed by Akatsuki

The three-tailed beast is a gigantic, turtle-like demon that Deidara and his new partner, Tobi, captured. This creature may be based on the Genbu or the Kappa.

What abilities this creature possesses remains unclear, as it did little to actually attack the two in its short appearance. It is clearly quite fast despite its size, as evidenced by its ability to keep up with Tobi, who was running on the water at the time. With the Three-tails distracted, Deidara molded an explosive clay fish in an attempt to capture it. It's unclear if this marked the end of the battle, as the remainder of the battle goes unseen. Tobi gloated of bringing the Three-tails down with his special jutsu, but Deidara thought otherwise. In its last appearance, Deidara is towing the unconscious beast with two large clay birds.

Unlike the other tailed beasts seen thus far, the Three-tails lacked a host. It is different from the Shukaku and the Demon Fox as it isn't intelligent, which makes it little more than a wild animal. According to Deidara, lacking a host made the beast weaker because it wasn't intelligent enough to control its own strength.

The Akatsuki leader called in his subordinates to perform the sealing ritual in chapter 327, and they complete sealing the beast in chapter 331.

Nine-Tailed Demon Fox

 * Name:, Viz "Demon Fox", English TV "The Nine-tailed Fox"
 * Creature type: Kitsune (Fox)
 * Host: Naruto Uzumaki
 * Unique traits: Near-limitless chakra, incredible strength
 * Status: Active
 * Seiyu: Tesshō Genda
 * Voice Actor: Paul St. Peter

The nine-tailed demon fox is a truly powerful beast; a single swipe of one of its nine tails can raise tsunamis and flatten mountains. After the demon fox attacked Konohagakure, the Fourth Hokage sealed it into the newborn Naruto by using the Dead Demon Consuming Seal, sacrificing his own life to do so.

The demon fox is a beast of almost pure malevolence. It is intelligent, and has a scathing and sadistic personality. However, it has a sense of honor, and seems to possess a respect (if merely a loathing one) for Naruto and the Fourth Hokage. Additionally, it has a distinct sense of pride and became rather angry and scornful at Naruto when he rejected its chakra when facing Sasuke in the Grass Country arc, though this might have merely been anger over missing an opportunity to partially usurp control over Naruto's body.

As the demon fox's host, Naruto has accelerated healing, almost unrivaled stamina, and access to the demon fox's immense amount of chakra. The near-limitless chakra allows Naruto to perform his signature jutsu, Shadow Clone Technique, seemingly without limit. He is even able to summon Gamabunta the "Toad Boss", a normally Kage-level feat requiring an amount of chakra proportionate to the size of the summoned creature.

Naruto typically accesses this prodigious supply of chakra from the demon fox when during extreme emotional states or life-threatening situations. When he first accessed it, the demon fox's innate rage took over Naruto's mind, causing him to strike out at whatever was near him at the time. Afterwards, Naruto learned to exercise more control over the chakra, and he can now retain his mental state when drawing upon small amounts of the demon fox's chakra. After Jiraiya's training, Naruto learns to summon a small degree of the demon fox's power at will. To do this, Naruto travels into his own mind (depicted as a sewer) and demands that the demon fox give him its chakra. He calls it "rent". The demon fox seems to comply simply because it is amused by Naruto's bravery.

The demon fox's chakra is not without its drawbacks, however. As Naruto draws on more of the demon fox's chakra, his own personality becomes supplanted by the fox's. The degree to which this occurs is proportionate to how much chakra Naruto draws upon. The effect on Naruto's personality becomes significant once he begins accessing his 'tailed' transformation states. The tailed transformations appear as a fox-shaped aura of red chakra surrounding him. The number of 'chakra tails' that extend from the aura indicate its power level, and its effect on his personality. In the one-tailed to three-tailed states, Naruto's personality remains dominant, but he acquires some animalistic behaviors, such as standing on all fours, fighting mercilessly, and a distinct bloodlust. In his four-tailed state (the highest seen so far), the demon fox's personality becomes dominant. Naruto becomes immensely powerful and destructive in this state, enough so to overwhelm even Jiraiya and Orochimaru. Unfortunately, this state also leaves him unable to distinguish between friend and foe. Such a large amount of chakra requires stability, so it densely molds around him. As Yamato stated, his body is just a "skeleton" for the chakra. The intense aura created from it both shields and harms him, burning off all his exposed skin and causing him to bleed from every pore. This, combined with the accelerated cell regeneration, weakens Naruto and shortens his lifespan; much like Tsunade's accelerated regeneration jutsu causes her to age faster.

In the event of the demon fox manifesting, Naruto's sensei, Jiraiya, prescribes a special written seal that is to be placed on Naruto's body. This seal suppresses the demon fox's chakra and restores Naruto to his normal self. In addition, Yamato has demonstrated a technique that will reverse Naruto's demon fox transformation.

The Third Hokage and Kakashi Hatake allude that if Naruto loses all control of the demon fox's chakra, the seal will break and the demon fox will be freed. Though the seal is unlikely to break on its own, the chances of it happening increase as Naruto draws upon the fox's chakra. In recent chapters, Jiraiya has mentioned that the seal may be becoming weaker over time. This is evident in Naruto's transformations, which occur much quicker and with greater intensity than they did in the first part of the series, often against his own will.

Near the end of the Grass Country arc, it is revealed that demon fox is familiar with the Uchiha clan. The precise relationship between the clan and the fox is unclear as of now, but the fox mentions a Madara Uchiha, who possessed chakra more evil ("cursed", as described by demon fox) than the demon fox's own, a trait which Sasuke seems to share. Sasuke also demonstrates the ability to forcefully suppress the demon fox's chakra.

The nine tails of the demon fox is a reference to the belief that a fox may possess as many as nine tails. Generally, an older and more powerful fox will possess a greater number of tails, and some sources say that a fox will only grow additional tails after they have lived for a thousand years. After that period of time, the number increases based on age and wisdom. Foxes that appear in Japanese folktales almost always possess one, five, or nine tails, and not any other number.

Legend of the Tailed Beasts
According to some fans, the "Legend of the Tailed Beasts" is an epic story from Japanese folklore which Naruto author Masashi Kishimoto draws from to create the tailed beasts in his work. It appears, however, to be an example of internet-based fakelore which originated on Chinese websites.

The veracity of the legend breaks when it is cross-referenced with non-fandom sources on Japanese folklore. For example, the isonade, which is held to be the three-tailed beast in this account, is in fact equipped with only one large, hook-covered tail, and the "houkou" (actually a Chinese creature called penghou), named as the five-tailed beast, has no tail at all.