Gyūki

, better known as is a tailed beast sealed within Killer B of Kumogakure after his cousin, cousin's uncle and cousin's father failed before him.

Background
According to Tobi, Gyūki came into being in the waning days of the Sage of the Six Paths' life; to prevent the Ten-Tails' resurgence, the Sage split up its chakra and used his ability to create nine separate, monstrous constructs of living chakra, which would become known as the tailed beasts. Some time after being created, the Sage of the Six Paths sat down with all the 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 was. Gyūki eventually fell into the possession of Kumogakure.

However, its ferocity was so great that none of its former jinchūriki could control it. They would lose control, and Gyūki would go on a rampage and destroy the village, requiring the Third Raikage to form a special coalition to subdue it. During one of its rampages, the Third fought Gyūki alone allowing his comrades to escape. During this encounter the Third managed to cut all of the beast's tails off, but both him and Gyūki collapsed with their techniques before they could finish the battle. During another encounter the Third extracted it from its previous jinchūriki, and sealed it within the Kohaku no Jōhei. Many villagers lost their lives during these episodes and Gyūki lost one of its four horns to A after the said horn pierced Motoi's father. It was ultimately sealed within Killer B, who was five at the time, through the Iron Armour Seal. B would go on to tame and control Gyūki through rigorous training within the Falls of Truth.

At some point in the past, one Kumo-nin attempted to mimic the Gold and Silver Brothers by eating one of Gyūki's chakra meat tentacles in the hopes of gaining the power like a jinchūriki, but died in the process.

Personality
Since Killer B is one of the few jinchūriki to gain control over his tailed beast, his relationship with Gyūki is very relaxed. Where the Nine-Tailed Demon Fox constantly threatens its jinchūriki and must be either restrained or confined to be spoken to, B and Gyūki can talk leisurely, with B even sitting on its nose. However, B tends to annoy Gyūki to comical effect; his serious and no-nonsense demeanour often contrasts with B's tendency to goof off whenever he likes, adding fuel to Gyūki's irritation to its vessel. Gyūki is not above bad-mouthing B as a result. Gyūki is also known to scold him in serious occasions as shown when it criticised B for rapping in his fight with Kisame when he should have been completely focused on their opponent. Because of this, Gyūki appears to be much more noteworthy than B as far as responsibility is concerned. Before B learned to control it, Gyūki was infamous to be wild, and violent. It also went on many rampages whenever its former jinchūriki would lose control of it.

Despite Gyūki's strong relationship with Killer B, its main goal, like the other beasts, is self-preservation. For example, it was more than willing to be released and attack Kisame Hoshigaki despite Sabu and Ponta being close by. Gyūki is also shown to have a good analytical ability, as it told Killer B that if he left Ponta and Sabu and run in the opposite direction Kisame and the water will follow him and they (Sabu and Ponta) would be freed. Gyūki mentioned that it used to be much more aggressive and violent but that Killer B changed it. It also said that it doesn't like the Nine-Tails but insisted that was no reason for B to refuse to help Naruto take control of the beast, hinting a benevolent side. Since then, both the beast and B have taken a liking to Naruto. Gyūki also tends to reprimand B. This is usually shown in a comical manner as when it bumped B in the head when the latter started to mention in a perverted matter how Yugito's chakra receivers were embedded in her left breast.

With regards to its relationship with the other tailed beasts, Gyūki maintaining that they had their own emotions and personalities has expressed dislike of the Nine-Tails' habit of ranking their strength based on their number of tails and has also stated that seeing another beast being forcefully controlled angered the rest of them greatly.

Appearance
Gyūki resembles an ushi-oni with four long horns on its head, similar to that of a Jacob sheep. It also has a fifth horn like protrusion on its chin, which appears to have been damaged, much like its lower left horn, part of which was sliced off in battle by A. It has a muscular upper-body structure, with a hunched back similar to an American bison, arms with spiked protrusions on the elbows, and hands with opposable thumbs like that of a human. It has no hind-legs, instead its lower half is made up of its tails which consist of eight tentacles that resemble the cephalopod arms of an octopus. These tails will grow back in the event that they are sliced off. It is also extremely massive, matching the Giant Squid in size.

Abilities
Gyūki was said by both Kisame and the Nine Tailed Demon Fox to be the second strongest of the tailed beasts. With its great supply of chakra, it can fire massive chakra blasts. Despite their massive size, its horns are incredibly sharp, coupled with Gyūki's massive physical strength it is able to easily impale a human being. During Naruto's battle with the Nine-Tails within his subconscious, it was shown that Gyūki had enough strength to temporarily restrain and contain a direct Tailed Beast Ball from the Nine-Tails, but was knocked out of the battle afterwards because of it. Its strength is such that it could stop the Three-Tails in full motion using only its extended tentacles, along with swiping the Five-Tails aside at the same time. It is able to endure being burned by Amaterasu for a considerable amount of time, and continue battle after being gored by the Five-Tails and slammed by Son Gokū. Its tentacles offer it several additional appendages with which to interact with its surroundings and strike targets, but they are also easily severed. Even with its immense size, it has shown a high level of speed when it attacks, and even fast enough to block Amaterasu with its fist. A single Tailed Beast Ball from it could penetrate nine of the thirty-six barriers without even exploding. Going with its octopus theme, it can also produce ink to blind opponents as well as form ink clones to bind the enemies. It can also generate enormous tornadoes which can destroy an entire forest with ease.

Gyūki has been shown to be very intelligent, explaining the mechanics of the Tailed Beast Ball to Naruto, the weaknesses of his Nine-Tails Chakra Mode, as well as pointing out that until he and the Nine-Tails reach a formal agreement, Naruto will not be able to fully transform or perform the Tailed Beast Ball. Gyūki even coached B in tactics on how to counter Kisame's water-based techniques. He is also very perceptive as he later worked out that the Gold and Silver Brothers were revived, after witnessing Naruto sense the Nine-Tails' chakra coming from outside of the training place that he and B were confined, correctly deducing that Orochimaru's Impure World Resurrection was being used by someone participating in the war.

Activity inside Killer B
As he has full control over Gyūki, it's jinchūriki, Killer B, can transform himself into the Eight-Tails and access its high-level chakra without losing control. Killer B is one of two jinchūriki who is known to be able to fully control his tailed beast's powers. Gyūki even acts as his partner in battle, disturbing his chakra in order to break illusions cast from even the Mangekyō Sharingan, as well as give B advice as to how to fight his opponents.

Invasion of Pain Arc
When Taka arrived at Kumogakure in an attempt to capture Killer B, he battled them to the point of annoyance. With his great control over his demon, Killer B transformed himself into Gyūki, and proceeded to terrorise Taka. As Gyūki attacked, Suigetsu commanded a wave of water, attempting to defeat it. Gyūki understood that Suigetsu had the advantage given that they were surrounded by water, so it then charged a Tailed Beast Ball and fired it at Suigetsu, defeating him.

After Sasuke activated his Mangekyō Sharingan and released Amaterasu on Gyūki, it fell into pain by its flames. As one of its tails was about to fall on Karin, Sasuke cut it with Chidori Sharp Spear. Killer B disguised himself as the cut part of the tail and escaped. Killer B was then seemingly captured by Taka and was given to Tobi. Killer B's brother, the Fourth Raikage, swore that Akatsuki would pay for what they had done.

It was later revealed that Killer B faked his capture. After Taka left, he and Gyūki left the lake and Killer B took this opportunity to take a "vacation" from being a guardian. As Gyūki commented that a new era was coming, Killer B thought it was going to be his singing career.

Five Kage Summit Arc
As Kisame attacked Killer B, Gyūki demanded B to let him out. However, B reminded him that he would just kill Sabu and Ponta in the process of protecting itself. With this, Gyūki begrudgingly let B use the version 2 form, as well as giving B advice during the battle. However, as Kisame knocked B out, Gyūki yelled at him to wake up, as both B and it were nearly out of chakra. Kisame then prepared to finish the battle as the Raikage arrived and helped B kill "Kisame".

Confining the Jinchūriki Arc
As Naruto Uzumaki and Yamato entered the Land of Lightning, in the Allied Shinobi Forces' efforts to keep the jinchūriki away from Akatsuki, they were attacked by a giant squid. Killer B, in his full Eight-Tails form, forced the squid back and saved the ship. Upon seeing it, Naruto realised that Gyūki and B were the "octopus" he had been looking for to guide him to control the Nine-Tailed Demon Fox. He asked B to train him, but B refused. After B was done training with some bears in the forest, Gyūki tried to convince B to train Naruto, stating that even though it wasn't fond of the Nine-Tails, it still thought B should train him since they are both jinchūriki.

Shinobi World War Arc
When Naruto failed to fully transform into the Nine-Tails, Gyūki requested that B let him speak with Naruto. He explained the risks of using a tailed beast's chakra, and how using it meant that the Nine-Tails could deplete Naruto's chakra, because when Naruto uses the Nine-Tails' chakra, it can take his. It explains that Naruto won't be able to transform fully until he can reach an agreement with the Nine-Tails, which it recognises as unlikely, noting that it and B used to be like that. It also says that because of that, he won't be able to learn the Tailed Beast Ball. When it is done, B changes back to his normal self.

It was later surprised at how Naruto was able to discern the chakra coming from Kinkaku and Ginkaku despite being secured in the training zone and then told B to stop Naruto from leaving the temple, but failed as Naruto was able to trick B into letting him out. Later, after B and Naruto encounter Nagato and Itachi Uchiha on the battlefield, a battle starts and Itachi traps Killer B in a genjutsu. Gyūki breaks the genjutsu for B, telling him to "snap out of it".

He later reprimands B for taking too many breaks to urinate and for letting Naruto go ahead of them. When Naruto contacts them through Inoichi, Gyūki talks to him about the time he fought the Third Raikage. When asked about the Third's scar, he initially thought that he had caused it with his Tailed Beast Ball, but then remembers that they both ended up collapsing from exhaustion during the battle. Both were still holding their techniques in their hands when they collapsed. Later, when Naruto and Killer B encounter Tobi and his Six Paths of Pain, Gyūki recognises Yugito Nii among them and figures out the others are the other deceased jinchūriki. After the initial assault from the dead jinchūriki, it tells him to be careful or he will end up just like them.

After the revived jinchūriki enter their tailed forms, Gyūki tells a bewildered Killer B, that Tobi must have turned them back into jinchūriki after reviving them. As B heads out to attack them, he tells him to be careful as he sensed a change in the other tailed beasts. After escaping Yugito's onslaught, Gyūki surmises that with the aid of the Sharingan and the Rinnegan, the jinchūriki's abilities had been greatly enhanced. Asking to speak to Naruto as well then begin formulating a counter strategy. After B reveals the location of the chakra receivers and Naruto's failed attempt to destroy Rōshi's, Gyūki tells B that the forest was a hindrance for their side and as such, B knew what he had to do. With that B assumes the form of Gyūki, prepared to destroy the entire forest. In this form, he attacks the revived jinchūriki with Tailed Beast Eight Twists, incapitating them, and attempts to seal them. Their opponents, however, enter their "Version 2"-like states, freeing themselves, and start attacking Naruto and B. The latter catches transformed Utakata, who however frees himself oozing alkaline. Next, B is attacked with lava from below by Rōshi and then knocked out by Han who had fully transformed into the Five-Tails.

As B and Gyūki try to find out if each other were all right, he later asks Naruto if he heard the voice of the Five-Tails. He then declares that the tailed beasts had their own emotions and watching one of their own being treated like that irritated them. The Nine-Tailed Demon Fox however retorts that ninja have always treated them like pets and that it and B were the only exceptions to this causing Gyūki to contemplate on his statement. After being cut off from revealing what was going on with the Nine-Tails, Gyūki then chastises the beast for always ranking them based on their number of tails, something that the One-Tailed Shukaku resented it for. As Naruto decides to reactivate the Nine-Tails Chakra Mode and B advises against the use of shadow clones, Gyūki tells B that Naruto should have been in critical condition after using so much of the beast's chakra, leading Gyūki to believe that it had stopped taking Naruto's chakra at some point. As Gyūki asks the Nine-Tails what happened between the two of them, the fox remembers Naruto's words to remove its hatred as well as his statement that having the fox sealed within him wasn't always bad.

Rebounding from being flipped over, Gyūki attempts to stop Son Gokū from swallowing Naruto, wrapping its tentacles around the beast. Gyūki beseeches Kurama to lend Naruto its power as it did with one of his clones. Kurama, however, states that he would not wag his tails at a jinchūriki in the same way that Gyūki did with B, causing Gyūki to question whether Kurama cared at all about what happened to Naruto. Gyūki later watches in horror as Naruto is swallowed by the great monkey. After Naruto successfully removes the chakra receiver, Gyūki watches on with shock as the beast is resealed into the Demonic Statue of the Outer Path in the blink of an eye. As Naruto rallies, telling the beast and B to get ready, it tells him that he and B would be taking to front-line while Naruto acted as support because he was still unable to transform into the Nine-Tails. After Naruto tells them it'd be fine because they were a pair of duos Gyūki wonders if Kurama had finally come around.

When Naruto started transforming into Kurama, the Eight-Tails got shocked that it decided to collaborate with Naruto. Leaping into action to aid Naruto, who was already battling the opposing five beasts, the beast stops the Three-Tails who was planning an attack from the Nine-Tails' blind spot. Simultaneously it buffets the Five-Tails telling it that the same attack would not work twice. As the Three-Tails frees itself from the beast's tentacles, it watches on in shock as the five beasts prepare a collaborative Tailed Beast Ball and wonders if Naruto was planning to negate the attack with a Tailed Beast Ball of his own even though he had never used it before.

After Naruto successfully frees all the remaining tailed beasts, Gyūki congratulates him.

Influence
In Japanese folklore, an is a massive, brutal sea-monster with the horned head of a bull and the body of a sea animal, like an octopus or a crab. It lives off the coasts of Japan and attacks fishermen.

Trivia

 * The Eight-Tails is the tailed beast with most known jinchūriki, all of which are also from the same family.
 * Gyuki is the last tailed beast to have his name revealed.

Quotes

 * (To Kurama)