Shukaku

, more commonly known as the, is a tailed beast that was sealed within Gaara of Sunagakure. It has been captured by Deidara, then extracted and sealed by Akatsuki.

Background
Shukaku first came into being in the waning days of the Sage of the Six Paths, who used his Creation of All Things ability to separate the Ten-Tails' chakra from its body and divide it into nine separate constructs in order to ensure that it would never resurface after his death. Some time after being created, the Sage sat down with all the young tailed beasts and told them that they would always be together even when separated, and that one day they would become one entity again with different names as well as forms than they did then when the time came for them to understand what true power is.

Citizens of Sunagakure came to believe that Shukaku was a of a corrupted Suna priest, and was originally sealed inside a tea kettle.

Shukaku had two jinchūriki in the past, one of which inspired the Third Kazekage to create the Iron Sand technique. Shukaku was eventually removed from their bodies, resulting in their deaths.

When Karura became pregnant with Gaara, her husband, the Fourth Kazekage, had Chiyo to seal Shukaku into Gaara while he was still in the womb, because of his three children, Gaara was the only compatible one with the beast. Before Karura died from a premature childbirth, she passionately told her son that she would protect him and according to her husband, her love seeped into the sand. However, Gaara couldn't properly control Shukaku's powers, killing or injuring several of Suna's shinobi and citizens. Deemed a failure, the Fourth Kazekage chose to test his son, ordering Yashamaru to assassinate him and also tell him that his mother never loved him, and that she was used as a human sacrifice for the sealing process. Gaara failed the test, fully releasing the rampaging Shukaku, to which the Fourth eventually used his Gold Dust to subdue the tanuki.

Personality
Shukaku is cunning, but also incoherent, giving it the demeanour of a madman. According to Gaara, because of its innate rage and blood-lust, Shukaku relishes the opportunity to kill anyone in sight, even more so during a full moon. Like all tailed beasts, Shukaku has a strong desire to preserve its own life, and as such, will grant its jinchūriki the power to control sand as well as allow them to transform into it in a state of need and blood-lust. Gyūki mentioned that Shukaku hates Kurama being the strongest biju beyond the fact that he has the most amount of tails because most biju can be measured by the number of tails and, obviously this would mean Shukaku is the weakest.

Appearance
Shukaku is a sandy-brown coloured tanuki, with black (dark blue in the anime) markings all over its face, body, and tail. It has a jagged, concave mouth and the sclerae of its eyes are black, containing yellow irides with pupils that each takes the shape of a black four-pointed star with four black dots around it. During the last remaining days of the Sage of the Six Paths, Shukaku in its youth looked the same as it does presently, only much smaller.

Abilities
Like all tailed beasts, Shukaku has an enormous supply of chakra. However, it does not have as much as Kurama. Shukaku has the power over wind, in which it uses to perform powerful attacks such as the Wind Release: Drilling Air Bullet; the ability to manipulate sand, using it as an effective weapon; and can perform the Tailed Beast Ball. At fully-released form, Shukaku's body is completely made of sand; as such he can ignore most damage that would otherwise be detrimental, as shown when he had one of his arms chopped off by Gamabunta and was still able to keep on fighting. Whenever Shukaku is sealed into its jinchūriki, it has the ability to eat away its host's personality, and influence him or her with its bloodlust behaviour whenever he or she sleeps, which leads its host to develop insomnia.

Activity inside Gaara
As Shukaku's jinchūriki, Gaara has the ability to move and levitate sand at will. Shukaku was at first believed to be the source of the automatic Shield of Sand, however the Fourth Kazekage told Gaara that this was due to his mother's love and will being in the sand, thus using Shukaku's sand manipulation for her own purpose; protecting Gaara from all harm. When angry or in a state of blood-lust, Gaara can use the sand in his gourd to take on the form of a miniature Shukaku, or even create a giant copy of Shukaku's body.

Invasion of Konoha Arc
During the Invasion of Konoha, Gaara transformed into his full Shukaku form during his fight with Naruto Uzumaki, who later summoned Gamabunta. When Gaara exposed himself on top of Shukaku's head and used the Feigning Sleep Technique, Shukaku took full control of its body and battled them. Shukaku's power was too much for Gamabunta to handle, resulting in both him and Naruto using the Combination Transformation to take the form of a giant fox (Kurama in the anime). Gamabunta used the form's claws and teeth to grab and restrain Shukaku, in order for Naruto to wake Gaara up with a punch, which suppressed Shukaku's power.

Ultimate Weapon Arc
In the anime, the goal of Four Celestial Symbols Men was to use Gaara's Shukaku chakra. Gaara was put under agony while Hoki from the Takumi Village absorbed a large portion of his chakra as well as Shukaku's to revive Seimei, which forced him to partially transform into Shukaku. However, when he thought about how Naruto would fight for his friends, Gaara himself managed to suppress Shukaku.

Kazekage Rescue Arc
During Gaara's time as the Fifth Kazekage, Deidara and Sasori from the Akatsuki were assigned to capture Shukaku. After Deidara defeated Gaara in combat and took him to Akatsuki's lair in the Land of Rivers, Shukaku was forcefully extracted from Gaara and placed within the Demonic Statue of the Outer Path. Though the extraction killed him, Gaara was resurrected through Chiyo's One's Own Life Reincarnation technique and has still retained the ability to control sand.

Trivia

 * literally means 'protector crane'.
 * A is a popular figure in Japanese folklore and is famous for its mischievous nature and abilities to shape-shift. Tanuki are also said be rivals to the kitsune, which created an old Japanese proverb:, meaning as much as two sly characters trying to outsmart one another. Shukaku being sealed inside a tea kettle is a reference to one Japanese tale called Bunbuku Chagama. In addition, Shukaku being claimed to be a corrupted Suna priest earlier in the series, has ties to a legend in the Kenchō-ji temple of a tanuki disguised as the shrine's priest.
 * Shukaku is the first tailed beast to have its name revealed in the series, and the only one that has not been resealed into its former host during the Fourth Shinobi World War, or have the characteristic red-chakra-shrouded Version 1 or Version 2 forms.
 * Despite Son Gokū claiming that jinchūriki did not care to learn their tailed beasts' name, Shukaku was known by its name.

Quotes

 * (To Naruto and Gamabunta while laughing) "I'm finally out!! And here's someone that I want to kill right now!!"