Gyūki

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

Background
Gyūki 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. 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
Gyūki is characterised as a tough and serious individual. It uses when referring to itself and often speaks in a somewhat rude dialect. In addition, Gyūki was also shown to have a good analytical ability, as it told Killer B that if he left Ponta and Sabu and ran away from them, Kisame and his water dome would follow him and they (Sabu and Ponta) would be freed. With regards to its relationship with the other tailed beasts, Gyūki mentioned that it and its brethren disliked Kurama for its habit of ranking their strength based on their number of tails. However, it insisted that was no reason for not helping Naruto to control Kurama's power, hinting a benevolent side. Since then, both Gyūki and B have taken a liking to Naruto.

In the past, Gyūki was infamous in Kumo for being wild and violent, as it went on countless rampages whenever its former jinchūriki would lose control of it. This was mostly likely due to its hatred against humans for oppressing and sealing it away many times. Gyūki kept on being that way until it was sealed within B, who would later change it after he bested it in one-on-one combat. Since then, Gyūki's relationship with B became more relaxed, with B even sitting on top of its muzzle while talking to Gyūki leisurely. However, B tends to annoy Gyūki to comical effect, as its 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 reprimand 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, and later when it comically bumped B in the head when the latter started to mention in a perverted manner how Yugito's chakra receivers were embedded in her left breast. Because of this, Gyūki appears to be much more noteworthy than B as far as responsibility is concerned.

Appearance
Gyūki is an ushi-oni with four long horns on its head, similar to that of a Jacob sheep. The lower left part of its horns was permanently sliced off in a battle with A. It would later most of its other horn after B detonated a Tailed Beast Ball inside the Ten-Tails' mouth. 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. During the last remaining days of the Sage of the Six Paths, Gyūki was smaller and its horns were much shorter.

Abilities
Gyūki was said by both Kisame and Kurama to be the second strongest of the tailed beasts. With its great supply of chakra, it is able to use the Tailed Beast Ball, as well as fire them in rapid succession at a target. A single Tailed Beast Ball from it could penetrate nine of the thirty-six barriers without even exploding. 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 Kurama within his subconscious, it was shown that Gyūki had enough strength to temporarily restrain and contain a direct Tailed Beast Ball from Kurama, but was knocked out of the battle afterwards because of it. Its strength is so great that it could stop Isobu in full motion using only its extended tentacles, along with swiping Kokuō‎ aside at the same time. It was able to endure being burned by Amaterasu for a considerable amount of time, and continued battling after being gored by Kokuō‎ and slammed by Son Gokū as well as being able to survive its own Tailed Beast Ball. 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. 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 Kurama 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 Kurama's chakra coming from outside of the training place that he and B were confined, correctly deducing that Orochimaru's Impure World Reincarnation 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 Gyūki and access its high-level chakra without losing control. Killer B is one of three 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. As Kisame then prepared to finish the battle, the Raikage and his bodyguards 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 Kurama's power. 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 Kurama, it still thought B should train him since they are both jinchūriki.

Shinobi World War Arc
When Naruto failed to fully transform into Kurama, Gyūki requested that B let it speak with Naruto. It explained the risks of using a tailed beast's chakra, and how using it meant that Kurama could deplete Naruto's chakra, because when Naruto uses Kurama's chakra, it can take his. It explains that Naruto won't be able to transform fully until he can reach an agreement with Kurama, 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.

Gyūki 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".

It 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, it initially thought that it had caused the scar with his Tailed Beast Ball, but then remembers that they both ended up collapsing from exhaustion during the battle, with both of their techniques still intact. 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 warns B 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, it 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. It asks to speak to Naruto as well begin to formulate 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, incapacitating 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 a 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 Kokuō.

As B and Gyūki try to find out if each other were all right, it later asks Naruto if he heard Kokuō's voice. It then declares that the tailed beasts had their own emotions and watching one of their own being treated like that irritated them. Kurama, 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 Kurama, Gyūki then chastises the beast for always ranking them based on their number of tails, something that 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 Kurama 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 it and B would be taking to front-line while Naruto acted as support because he was still unable to transform into Kurama. 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 transformed into Kurama, Gyūki got shocked that it decided to collaborate with Naruto. Leaping into action to aid Naruto, who was already battling the opposing five beasts, B uses Gyūki's tails to stops Isobu who attempted to attack Naruto's blind spot. Simultaneously B buffets Kokuō, telling it that the same attack would not work twice. As Isobu 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.

As the two Tailed Beast Balls collide, B grabs Rōshi's body and shields itself from the after-effects of the attacks. After Naruto successfully frees all the remaining tailed beasts, Gyūki congratulates him. Later, as Naruto mocks Tobi with the information he had just learned, B and, by extension, Gyūki looks on smirking. As the battle continues, B and Naruto launch a combination attack on the Demonic Statue of the Outer Path with a double uppercut knocking the statue to the ground following Kakashi Hatake and Might Guy's respective attacks. Gyūki later looks on as Tobi seemingly prepared to revive the Ten-Tails. After hearing Naruto's speech about his dreams, B revealed his sexual desires — leading Gyūki to be embarrassed for his host.

While the shinobi regroup and discuss the gash in Tobi's mask, Gyūki uses the opportunity to attack the statue. Moving in with a punch, it declared that the statue was wide open. However, his attack was deflected by Tobi's Uchiha Flame Battle Encampment barrier which burned its hand. Telling Naruto that its hand was okay, Gyūki prepared to launch the strategy that Kakashi had developed. Holding all the shinobi in his hands, Gyūki threw the trio towards Tobi. When they regroup after Tobi's arm is hit by a seemingly unseen attack, B listened to Kakashi's explanation of Tobi's technique and then enquired if all Space–Time Ninjutsu shared the same dimension. When told no, B told Naruto that it still would not be easy to land an attack on an intangible person. When Kakashi stated that their belief that Tobi was becoming intangible was incorrect, B enquired once again how it was possible for their two Sharingan to share the same dimension. With Gyūki bound by Tobi's giant chakra receivers, the beast is shocked to see Madara arrive on their battlefield. When Naruto questioned Madara as to what had happened to the Kage, Gyūki surmised that if he was here, then the Kage must be in a bad situation. The beast later thanked Naruto as the young man freed him from the stakes. As the battle with Madara ensued, Gyūki was seemingly knocked to the ground, leading it to comment on Madara's power. When an injured Guy told it that was why Madara was worth fighting, the beast told him that he shouldn't be pushing himself so hard.

As the battle waged on, the beast and Guy were restrained by Madara, before the Uchiha can land the finishing blow, he is intercepted by Naruto. After Might Guy's Daytime Tiger sends the legendary ninja flying away from them, Gyūki noted that Guy wasn't just acting tough. After breaking free of its constraints, Gyūki warned Naruto that the wood could suppress a tailed beast's power before turning its attention to the statue. Forming a collaborative tailed beast ball with Naruto, Gyūki fires it at the statue and believed it to be destroyed. Their celebration, however, was cut short when the smoke cleared and the Ten-Tails appeared on the battlefield. Questioning Kurama whether or not it really wanted to fight what stood before them, the ushi-oni is told by the fox that hiding wouldn't help anything. Standing alongside Kurama, who had taken charge of the situation, the beasts were attacked by the Ten-Tails before they could follow through with their strategy. Launching a continuous stream of Tailed Beast Balls at the beast, their attack was thwarted by the Ten-Tails and when the smoke cleared, Gyūki was missing. It was later revealed that it was warped away by Kakashi who releases the beast above the tailed beast launching a point-blank Tailed Beast Ball overhead the beast. After the Ten-Tails flicked the Tailed Beast Ball right back at Gyūki, Kurama was able to save both Gyūki and B before both tailed beasts ran out of power and proceeded to recuperate in order to regain their powers.

Having generated enough chakra, Gyūki and B jumped into action to protect the shinobi from a Tailed Beast Ball that the Ten-Tails was going to launch at them. Now fully transformed, B recklessly stuffed Gyūki's head into the Ten-Tails' mouth and launched his own Tailed Beast Ball, both of which detonated in the beasts' body causing it to fall and writhe in pain.

Video Games
Although Gyūki itself is not playable, B takes on its form as his awakening in Naruto Shippūden: Ultimate Ninja Storm 2 and Naruto Shippūden: Ultimate Ninja Storm Generations.

Trivia

 * 'Gyūki' is an alternate pronunciation for the name of the.
 * 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.
 * Gyūki is the tailed beast with the most known jinchūriki, most of whom are also from the same family.

Quotes

 * (To Kurama)