Gyūki

, more commonly known as the, is one of the nine tailed beasts. It has been in the possession of Kumogakure for decades, where it has been sealed into many jinchūriki. Its most recent jinchūriki, and the first to have any success in cooperating with it, is Killer B.

Background
Gyūki and the tailed beasts first came into being in the waning days of Hagoromo Ōtsutsuki, who used his Creation of All Things Technique to divide the Ten-Tails' chakra into nine separate bodies and giving each a name. Some time after being created, the Sage explained to the young tailed beasts that a link existed between them despite their separation. He also foretold of a day when they would be brought together again - though not as they were - and that at that time someone would emerge to show them what true power is. After Hagoromo's death, the tailed beasts drifted apart, apparently due to Kurama's belief that their number of tails was an indication of their strength.

Gyūki eventually fell into the possession of Kumogakure. However, its might was so great that none of its former jinchūriki - such as Blue B, and his uncle and father before him - could control it. They would lose control and Gyūki would go on a rampage, destroying the village and killing many villagers, requiring the Third Raikage to form a special coalition to subdue and seal it in the Kohaku no Jōhei. Despite its rampages, the Third Raikage believed a jinchūriki for Gyūki was too valuable of a war deterrent and decided to keep looking for a compatible one. During one of its rampages, the Third fought Gyūki one-on-one until they both collapsed from exhaustion. During another, Gyūki had one of its four horns lost to A, the offending horn having killed Furui. In the anime, Blue B's rampage was stated to be orchestrated by Orochimaru, who gave Blue B genjutsu-inducing pills to draw out Gyūki. Due to the pills, Gyūki had no recollection of the rampage.

Gyūki 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 jinchūriki-like power, 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. 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 Hoshigaki 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 Uzumaki 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 most likely due to its hatred against humans for oppressing and sealing it away many times. Gyūki maintained this behaviour until it was sealed within B, who would later change it after he bested it in one-on-one combat. Since then, Gyūki's personality has become much more relaxed, becoming close friends with B; even allowing him to sit on top of its muzzle while talking to it 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.

As a result, Gyūki is not above bad-mouthing B and is also known to reprimand him in serious occasions. This was seen when Gyūki 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 black receivers were embedded in her left breast and when Obito disappeared B was wondering if he escaped only for Gyūki to tell B to find him. This somewhat contradicts the original point of having a jinchūriki which is to control a tailed beast, but Gyūki seems to be more of the one in control than B. Because of this, Gyūki appears to be much more noteworthy than B as far as responsibility is concerned. Nonetheless, Gyūki formed a very strong bond with B, as even after being extracted from its jinchūriki, the tailed beast severed a piece of itself to help sustain B's life. Following its release from Kaguya, Gyūki expressed a desire to return to B, noting it had gotten used to his awful rapping and felt odd not hearing it.

Gyūki's relationship with its B's predecessor Blue B was unknown in the manga, other than the fact it would pounce on the "hole" in Blue B's heart and assume control over him. In the anime, however, Gyūki stated it had high hopes for Blue B, indicating it bore no ill will towards its former host.

Appearance
Gyūki is an ushi-oni with four long horns on its head, similar to that of a Jacob sheep. As a tailed beast, it is extremely massive, dwarfing entire forests and towers over large rock formations and buildings and matching the Giant Squid in size. The lower left part of its horns was permanently sliced off in a battle with A, and the right horns were destroyed by its own point-blank Tailed Beast Ball when fighting the Ten-Tails. It also has straight teeth, one of which was blown off during the point-blank Tailed Beast Ball. Following the Fourth Shinobi World War, it grew another tooth. Gyūki also 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. Instead of hind-legs, its lower half consists of its eight tails, which resemble the cephalopod arms of an octopus. These tails will grow back in the event they are sliced off. During the last remaining days of Hagoromo Ōtsutsuki, Gyūki was smaller and its horns were much shorter.

Abilities
Gyūki was noted by Kisame and Kurama to be the second most powerful of the nine tailed beasts. Even the Third Raikage, hailed as the greatest shinobi in Kumo's history, formed a special team to subdue and seal it during its various rampages, with the ushi-oni fighting the Third to a stalemate on one occasion. In addition, the Fourth Raikage once forbade B from fully transforming into Gyūki due to its great might. During the Fourth Shinobi World War, Gyūki held its own against two other tailed beasts despite suffering a past injury.

Chakra and Physical Prowess
As a tailed beast, Gyūki possesses a massive supply of powerful chakra and can share it with others. It can replenish its high reserves shortly after an entire day's usage. Should the need arise, it can disturb B's chakra with its own to dispel powerful genjutsu. Gyūki's tentacles, if severed, can be used as a medium for its chakra, such as creating a clone of its host, or transferring chakra to said host should the beast be extracted. A Kumo-nin who attempted to gain jinchūriki-like powers by eating one of Gyūki's tentacles died from the chakra instead.

Gyūki has immense physical strength, being able to temporarily restrain Kurama, contain a direct Tailed Beast Ball, and later overwhelm a charging Isobu and Kokuō at the same time. It is also deceptively fast, being able to strike quickly with its tentacles and block Amaterasu with its fist. Its incredibly sharp horns can easily impale a human being. Gyūki is also durable enough to survive its own Tailed Beast Ball, including a combined explosion of such attacks from itself and the Ten-Tails in the latter's mouth. Its tentacles allow it to better interact with the environment, such as generating enormous tornadoes. Defensively, they can help block explosions and shockwaves from a collision of gigantic Tailed Beast Balls, or slow down the velocity of a massive attack from the Ten-Tails. However, the tentacles can be easily severed by very sharp techniques such as the Chidori.

Ninjutsu
Like other tailed beasts, Gyūki can perform the Tailed Beast Ball and has shown great skill with it, firing it as multiple spheres in rapid succession or as a massive wave explosion. Its fully charged Tailed Beast Ball was powerful enough to devastate the entire Valley of Clouds and Lightning, penetrate nine of the thirty-six barriers without exploding, and even push the Ten-Tails' own point-blank Tailed Beast Ball back into its body, which temporarily injured the latter. Unlike most tailed beasts, Gyūki can also 'supercharge' a Tailed Beast Ball on its own, creating one many times its own size for much greater power. Going with its octopus theme, it can produce ink to blind its enemies, as well as form ink clones to bind them.

Intelligence
Gyūki is shown to be very intelligent and knowledgeable, explaining the mechanics of the Tailed Beast Ball to Naruto, the weaknesses of his Nine-Tails Chakra Mode, and how he would not be able to use the form's full output until he and Kurama fully cooperate. It even coached B in tactics on how to counter Kisame's water-based techniques. Gyūki is also very perceptive as it later worked out that the Gold and Silver Brothers were reincarnated, after witnessing Naruto sense Kurama's chakra coming from outside of the training place that he and B were confined in. From this, it correctly deduced that Orochimaru's kinjutsu was being used by someone participating in the Fourth Shinobi World War.

Pain's Assault
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 tailed beast, Killer B transformed himself into the Eight-Tails, and proceeded to terrorise Taka. As B attacked, Suigetsu commanded a wave of water, attempting to defeat it. B 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 B, 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 the Eight-Tails left the lake and Killer B took this opportunity to take a "vacation" from being a guardian. As the Eight-Tails commented that a new era was coming, Killer B thought it was going to be his singing career.

Five Kage Summit
As Kisame attacked Killer B, the Eight-Tails 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, the Eight-Tails begrudgingly let B use the Version 2 form, as well as giving B advice during the battle. However, as Kisame knocked B out, the Eight-Tails 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".

Fourth Shinobi World War: Countdown
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 the Eight-Tails and B were the "octopus" he had been looking for to guide him to control the Nine-Tails' power. He asked B to train him, but B refused. After B was done training with some bears in the forest, the Eight-Tails 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.

Fourth Shinobi World War: Confrontation
When Naruto failed to fully transform into the Nine-Tails, the Eight-Tails 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 the fox could deplete Naruto's chakra, because whenever Naruto used the Nine-Tails' chakra, it could take his. It explained that Naruto wouldn't be able to transform fully until he could reach an agreement with Nine-Tails, which it recognised as unlikely, noting that it and B used to be like that. It also said that because of that, he wouldn't be able to learn the Tailed Beast Ball. When it was done, B changed back to his normal self.

The Eight-Tails 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 encountered Nagato and Itachi Uchiha on the battlefield, Itachi trapped Killer B in a genjutsu, but Eight-Tails broke the genjutsu for B by disturbing his chakra flow. Ultimately, Itachi is able to break free of his control thanks to one of his crow that he stored inside Naruto using a powerful genjutsu. Itachi then aided Naruto and B against Nagato, ultimately sealing away Nagato. After Itachi explained the situation, he left Naruto and B to stop the Impure World Reincarnation.

The Eight-Tails later reprimanded B for taking too many breaks to urinate and for letting Naruto go ahead of them. When Naruto contacted them through Inoichi, the Eight-Tails talked to him about the time it 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 remembered that they both ended up collapsing from exhaustion during the battle, with both of their techniques still intact.

Later, in the anime, Motoi arrived to aid B. They were then approached by the reincarnated Blue B, B's predecessor as the Eight-Tails jinchūriki. Blue B revealed, to the Eight-Tails' shock, the ability to still use the tailed beast chakra cloak, entering his Version 2 form. As B entered Version 2 and clashed with Blue B, the Eight-Tails insisted to know how Blue B can still use that power. Blue B explained that the Eight-Tails' rampage from thirty years ago was in fact manipulated by Orochimaru, using a genjutsu-inducing drug to force out the ox. During the chaos, the Sannin member also harvested some of the Eight-Tails' severed horn. It was from the genetic material that Blue B obtained a recreation of the ox's chakra. As they battled, Motoi was defeated but saved by B. Seeing that B accomplished what he could not, Blue B was able to let go of his past and return to the afterlife.

Fourth Shinobi World War: Climax
Later, when Naruto and B encountered Tobi and his Six Paths of Pain, the Eight-Tails recognised Yugito Nii among them and figured out the others were the other deceased jinchūriki. After the initial assault from the dead jinchūriki, it warned B to be careful or he would end up just like them. After the revived jinchūriki enter their tailed forms, the Eight-Tails explained to a bewildered B that Tobi must have turned them back into jinchūriki after reviving them. As B head out to attack them, it told him to be careful as he sensed a change in the other tailed beasts. After escaping Yugito's onslaught, the Eight-Tails surmised that with the aid of the Sharingan and the Rinnegan, the jinchūriki's abilities had been greatly enhanced. It asked to speak to Naruto as well begin to formulate a counter strategy. After B revealed the location of the black receivers and Naruto's failed attempt to destroy Rōshi's, B in his Tailed Beast Mode leveled the entire forest to get rid of their disadvantage. He then attempted to seal them, but Tobi forced his Paths to enter their Version 2 forms, freeing themselves, and they started attacking Naruto and B. The latter caught a transformed Utakata, who quickly freed himself by oozing alkaline. Next, B was attacked with lava from below by Rōshi and then knocked out by Han who had fully transformed into the Five-Tails.

As B and the Eight-Tails tried to find out if each other were all right, it later asked Naruto if he heard the Five-Tails' lamented voice. It then declared that the tailed beasts had their own emotions and watching one of their own being treated like that irritated them. The Nine-Tails, however, retorted that shinobi had always treated them like pets and that it and B were the only exceptions to this, causing the Eight-Tails to contemplate on its statement. The Nine-Tails then went on to state that according to number of tails, the Eight-Tails was second after it, so it should just hurry up and finish things, and then proceeded to fake going to sleep. After being cut off from revealing what was going on with the Nine-Tails, the Eight-Tails then chastised the fox for always ranking them based on their number of tails, something that the One-Tail resented it for. As Naruto decided to reactivate the Nine-Tails Chakra Mode and B advised against the use of shadow clones, the Eight-Tails explained to B that Naruto should have been in critical condition after using so much of the fox's chakra, leading the Eight-Tails to believe that it had stopped taking Naruto's chakra at some point. As the Eight-Tails asked the Nine-Tails what happened between the two of them, the fox remembered Naruto's words to resolve its hatred as well as his statement that having the tailed beast sealed within him wasn't always bad.

Rebounding from being flipped over, B attempted to stop the Four-Tails from swallowing Naruto, wrapping its tentacles around the beast. The Eight-Tails beseeched the Nine-Tails to lend Naruto its power as it did with one of his clones, but the fox stated that it would not cooperate with its jinchūriki as easily as the ox did with B, causing the Eight-Tails to question whether the Nine-Tails cared at all about what happened to Naruto. The Eight-Tails later watched in horror as Naruto was swallowed by the Four-Tails. After Naruto successfully removed Son Gokū's black receiver, the Eight-Tails watched on with shock as the beast was resealed into the Demonic Statue of the Outer Path in the blink of an eye. As Naruto rallied the Eight-Tails and B to get ready, the ox told him that it and B would be taking to front-line while Naruto could act as support because he was still unable to transform. After Naruto reassured them it'd be fine because they were a pair of duos, the Eight-Tails expressed shock after seeing Naruto entering his Tailed Beast Mode with Kurama.

Leaping into action to aid Naruto, who was already battling the opposing five beasts, the Eight-Tails used its tentacles to stop the Three-Tails' attempt to attack Naruto's blind spot. Simultaneously, the ox buffeted the Five-Tails, telling it that the same attack would not work twice. As the Three-Tails freed itself from the ox's grasp, it watches on in shock as the five beasts prepared a collaborative Tailed Beast Ball and wondered 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 collided, Gyūki grabbed Rōshi's body and shielded itself from the after-effects of the blast. After Naruto successfully freed all the remaining tailed beasts, Gyūki congratulated him. Later, as Naruto mocked Tobi with the information he had just learned, B and, by extension, Gyūki looked on smirking. As the battle continued, B and Naruto launched 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 looked 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 its jinchūriki.

While the shinobi regroup and discuss the gash in Tobi's mask, Gyūki used the opportunity to attack the statue. Moving in with a punch, it declared that the statue was wide open. However, its attack was deflected by Tobi's Uchiha Flame Formation barrier, which burned its hand. Gyūki then prepared to launch the strategy that Kakashi had developed. Holding all the shinobi in his hands, Gyūki threw the trio towards Tobi. When they regrouped after Tobi's arm was 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 black 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.

With the chakra shrouds protecting them dissipated, Naruto being healed, and Kurama kneading more chakra, B and Gyūki announced that it was time for them to take centre-stage once again to buy the duo some time to recover as Gyūki noted that the Ten-Tails would become unstoppable if it underwent its final transformation. With Shikamaru's strategy initiated, and the shinobi begin to construct earthen — albeit feeble — defences, B interceded and attempted to throw the attack off-trajectory. However, with none of their combined efforts seemingly working, and the situation looking dire, the Alliance is saved by the arrival of the Fourth Hokage, unbeknownst to them as B looked on puzzled that the attack had seemingly just vanished.

Birth of the Ten-Tails' Jinchūriki
As Obito emerged within the barrier some time later after sealing the beast inside himself, B asked Gyūki whether or not that was the beast's final form. It told him that it was not and that from all appearances, it seemed that the beast had been sealed before reaching its final form. When B asked if he could feel Kurama's Yin and Yang chakra, Gyūki noted that it wasn't just Kurama's chakra. When Obito recreated a full-blown replica of the Ten-Tails' tree form, its roots started chasing and absorbing chakra from anyone in its path. Ultimately, while worn out, B with Samehada's aid was able to destroy the roots that had confronted him. After Naruto, with the help of Sasuke and the Konoha 11, delivered a devastating blow against Obito, it forced the chakra of all the tailed beasts to come out of his body. B then grabbed Gyūki's chakra while Naruto, Gaara, and the rest of the Shinobi Alliance pulled the others to reduce Obito to a shell of the Ten-Tails' tree form and prevent the flower atop the tree from blooming.

When Madara ran towards the tailed beasts, both Shukaku and Gaara conjured numerous sand bullets and were able to restrain the Uchiha's movements. Using the opportunity to attack, the tailed beasts each took a swing at their opponent, giving sand-manipulating duo an opening to use their Desert Layered Imperial Funeral Seal, but Madara managed to escape the sand pyramid with his Susanoo. After evacuating the wounded shinobi from the battlefield, Gyūki and the other tailed beasts joined Naruto and Kurama in assaulting Madara, but the Uchiha survived their attacks and retreated to a safe distance. After he received his own right Rinnegan eye from a White Zetsu clone, Madara quickly summoned the Demonic Statue of the Outer Path from Obito's body, and used the Rinnegan to repel the tailed beasts. With the tailed beasts stunned, Madara then proceeded to chain them up and prepared to remove Yang-Kurama and Gyūki from their jinchūriki. Struggling against its confines, Gyūki apologised to B as it was extracted and sealed within the statue along with the other tailed beasts, but not before cutting off one of its tentacles, letting B survive through the chakra within it.

Later, after Madara succeeded in becoming the Ten-Tails' jinchūriki, a reformed Obito managed to steal some of Gyūki's chakra along with some of Shukaku's. When Obito sealed Yin half of Kurama into a dying Naruto to save his life, Obito also sealed the Gyūki and Shukaku's chakra portion into Naruto. Inside Naruto's subconscious, Gyūki, Shukaku, and Yin-Kurama found the young jinchūriki talking with the spirit of Hagoromo Ōtsutsuki. As the other six tailed beasts manifested to join in the meeting, they all voiced their shared belief to the Sage that Naruto was the child of prophecy.

Kaguya Ōtsutsuki Strikes
After Madara's ambitions were cut short by Black Zetsu, who revealed to be the silent manipulator of shinobi history since it was first created by Kaguya Ōtsutsuki, the black entity used Madara's body as a medium to resurrect its creator. During the battle against the tyrannical princess, Gyūki and the other tailed beasts continued to support Naruto by giving him their combined power to overwhelm her. Ultimately, Kaguya was defeated by Naruto and Sasuke, who used the Six Paths — Chibaku Tensei to eject all the tailed beasts from her and seal her away inside a newly-created moon within her own dimension.

After the spirits of Hagoromo and the past Kage summoned both the tailed beasts and Team 7 back to the real world, the tailed beasts began to discuss their plans for the future since they were finally free. Gyūki, who was asked by Yang-Kurama on the subject, surprised the fox when it expressed its desire to return to B. Sasuke, however, made his own intentions known: removing as many people as possible who could get in the way of his plans of leading the world through a revolution to do away with current shinobi systems, including killing all the current Kage and tailed beasts. Just as Sasuke swiftly subdued the tailed beasts with his Rinnegan and sealed them within his Chibaku Tensei, Naruto reassured the tailed beasts that he would save them once again. After Naruto was able to defeat and reform Sasuke, the two dispelled the Infinite Tsukuyomi and Sasuke released Gyūki along with the other tailed beasts from their prisons. Gyūki then returned as it desired to B, getting resealed within its partner.

Epilogue
Years later, B complained about how he felt bored and, as such, should go and see how Naruto was doing, only for Gyūki to note that Naruto was busy, unlike B.

Boruto: Naruto the Movie
Killer B is captured by Momoshiki and Kinshiki Ōtsutsuki, and brought to another dimension. THey extract Gyuki from inside him and were unimpressed with Gyuki's power. Gyuki tried to attack them but his power was absorbed through Momoshiki's Rinnegan. The two then presumably destroyed Gyuki and threw Killer B into a river to let him drown. The end credits reveal that Gyuki and Killer B survived.

Video Games
Although Gyūki itself is not playable, B takes on its form as his awakening in Naruto Shippūden: Ultimate Ninja Storm 2, Naruto Shippūden: Ultimate Ninja Storm Generations, Naruto Shippūden: Ultimate Ninja Storm 3, and Naruto Shippūden: Ultimate Ninja Storm Revolution.

Trivia

 * , which literally means "ox ogre", is an alternate pronunciation for the name of the ushi-oni. In Japanese folklore, an ushi-oni is a massive, brutal yōkai with the horned head of a bull and the body of an octopus, a crab, or a spider. One legend says that it lives off the coasts of Japan and attacks fishermen.
 * Gyūki is the only tailed beast that apparently has been shown to have a permanently damaged body.

Quotes

 * (To Kurama)