Isobu

, more commonly known as the, is one of the nine tailed beasts. It was last sealed within Yagura Karatachi of Kirigakure.

Background
Isobu 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. In the anime, before his death, Hagoromo sent Isobu to live in a temple built for the purpose of protecting it in a region surrounding a large misty lake that would later become part of the Land of Water.

During the First Shinobi World War, Hashirama Senju captured eight of the tailed beasts and sold Isobu and Saiken to Kirigakure at the Five Kage Summit, as a sign of friendship and to ensure a balance of power amongst their new villages. Decades later, Kirigakure — having been manipulated by Madara Uchiha — sealed Isobu into the Konohagakure shinobi, Rin Nohara. They plotted for Rin to be taken back to her village as a Trojan horse, releasing the tailed beast to wreak havoc in Konoha. This failed, however, as Rin was fully aware of their schemes and opted to kill herself at hands of her friend and fellow team-mate, Kakashi Hatake before their objectives could come to fruition. Eventually, Isobu was revived and sealed within its next jinchūriki — Yagura, the Fourth Mizukage, who managed to gain complete control and harmony with it. However, Yagura was placed under the genjutsu of Obito Uchiha as Mizukage until his death when its dispelled. Some time later, it once again revived however it wasn't resealed into a host by the time it was encountered.

In the anime, Tsunade states that Isobu disappeared after the Third Shinobi World War.

Personality
Isobu speaks in a timid manner, referring to itself as which is usually used by young boys. Seeing as Yagura had full control of it and befriended it, it's assumed that Isobu isn't as rude or outspoken as some of the other tailed beasts and got along with its jinchūriki.

Appearance
Isobu primarily resembles a large turtle, but with a crab-like shell, spikes all over its body, and three shrimp-like tails. Under its shell, it has red, muscle-like tissue. It has a pair of human-like arms and hands, but no hind-legs. His face is concealed between a large forehead and lower jaw — both of which have spikes. Its eyes are red and have crimson pupils. In the anime, the eyes are red with yellow pupils.

Its right eye is constantly closed. In the anime, Guren speculated this was because its eyes were the only soft parts of its body, being heavily-armoured, and thus kept one eye closed to cover more vulnerable spots. During the last remaining days of the Sage of Six Paths, Isobu was essentially much the same in appearance, albeit smaller in size with shorter spikes around its body, but was still many times larger than the Sage.

Abilities
As a tailed beast, Isobu possesses an enormous amount of chakra that it can transfer to others and can create the Tailed Beast Ball. It also has the ability to create coral and swim at very high speeds. Kirigakure was so confident of its destructive potential that they, under the influence of Madara Uchiha, intended to unleash Isobu in the midst of Konohagakure to destroy the village. In the anime, it could produce a hallucinogenic mist that exploited the victim's insecurities and forced the victim to face them.

Physical Prowess
Isobu can roll into a ball to move about quickly and attack its opponents, making full use of the protrusions on its shell in a manner similar to the Akimichi clan's Spiked Human Bullet Tank. Isobu's tough skin and shell also grant it additional defence, allowing it to withstand nearly all forms of attack. It can also use any of its three spiked tails to strike its opponents and break through most defences. In the anime, Isobu's only known physical weakness is its eye; as tough as its skin and shell are, it cannot harden its eyes and thus seems to keep one closed at all times.

Ninjutsu
In the anime, Isobu's abilities were greatly elaborated upon. It could create shockwaves to repel attacks and produce large tidal waves around it, enabling it to overwhelm Guren's Crystal Release several times over the course of their battle. When Isobu ate something, thousands of miniature versions of itself would attack what was eaten within its stomach, presumably to speed up the digestion process. It was also shown capable of Space-Time Ninjutsu, materialising an entrance to a separate dimension in which it could hide its presence, until it was ready to return to wherever it chooses.

Nature Transformation
As a turtle, Isobu has an affinity for Water Release. In the anime, it has shown to fire powerful water blasts that are capable of destroying an entire cliff side.

Akatsuki Suppression Mission
In the manga, Tobi and Deidara confronted the beast around the same time Naruto Uzumaki had begun his Wind Release training, to which it responded by beginning to chase Tobi. With the Three-Tails distracted, Deidara moulded an explosive clay fish in an attempt to capture it. It was unclear if this marked the end of the battle, as the remainder of the battle went unseen. As the two towed the Three-Tails to the Akatsuki's lair after the battle, Tobi gloated at bringing the Three-Tails down with his special technique, but Deidara thought otherwise. It was later sealed in the sealing statue.

Three-Tails' Appearance
In the anime, Orochimaru instructed Kabuto Yakushi and Team Guren to take a young boy named Yūkimaru to a lake. After they arrived, Kabuto forced Yūkimaru to release all of his chakra, which caused the Three-Tails to begin to surface from the lake. With Guren's help, the beast was completely revealed, and they attempted to capture it. Their attempts proved insufficient, however, and the beast created a large tidal wave to wash its attackers away.

The tidal wave gained the attention of a nearby group of Konohagakure ninja, who tried to use Four-Corner Sealing Barrier to permanently trap the beast in its own dimension. Just as the sealing began to work, the Konoha ninja were interrupted by Guren, which prompted the beast to attack them all. Yūkimaru was able to calm the beast down temporarily, but, after he became tired, the Three-Tails turned its attention to him. Guren and Naruto Uzumaki came to his defence, but were swallowed in the process. With the help of their allies on the outside, they were able to escape, and the Konoha ninja tried once more to seal the beast.

Just when the sealing was almost complete, Yūkimaru, angered by the apparent death of Guren, empowered the beast to break free of its restraints. The Three-Tails went on a rampage, attacking everyone nearby and crushing Nurari, Kigiri, and Kihō. Its attempts to attack Yūkimaru, however, had no effect. It was only through the use of the Wind Release: Toad Oil Flame Bullet that the beast was driven away. The sealing attempt was left to Anbu members, and the remaining Konoha ninja returned home. Deidara and Tobi of Akatsuki soon found these Anbu members and disposed of them.

Fourth Shinobi World War: Climax
After Son Gokū was resealed into the Demonic Statue of the Outer Path, Tobi, who was intent on going all-out from that point on, forced Yagura to fully transform into the Three-Tails. The opposing tailed beasts prepared to attack the shinobi, but they were rebuffed by a fully-transformed Naruto. Wasting no time in their attacks, the Three-Tails evaded Naruto and Kurama's pile-drive attack by rolling out of the way to counter-attack after the Six-Tails had incapacitated them, but the turtle was stopped by the Eight-Tails. Freeing itself from the ox's grasp, the opposing beasts regrouped and prepared a collaborative Tailed Beast Ball, which was met by one from Naruto and Kurama.

As Naruto entered a deeper plane of the tailed beasts' consciousness, Isobu (who remembered meeting him in the anime) introduced itself to the young shinobi. Later, as Isobu was freed from the chakra receiver, it affirmed Kurama's belief that Naruto was the person the Sage of the Six Paths had spoken about so long ago before being resealed into the Demonic Statue of the Outer Path.

Birth of the Ten-Tails' Jinchūriki
Isobu appeared alongside the other tailed beasts with the exception of Gyūki and Shukaku when the Ten-Tails looked down at Naruto. The image of the tailed beasts, along with a silhouette of the Sage of Six Paths, drove the Ten-Tails to a fit as it evolved further. Due to the combined teamwork of the Allied Shinobi Forces, Isobu, alongside the other imprisoned tailed beasts, was later pulled out of Obito and thus freed.

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. As Naruto in Tailed Beast Mode pinned Madara down with a tail, Isobu and the other tailed beasts joined in and did the same to increase the damage, 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 chained them up and sealed them back into the Demonic Statue.

Later, the chakra Isobu transferred to Naruto earlier, manifested within Naruto's subconscious along with the other tailed beasts to speak with the young jinchūriki and the spirit of Hagoromo Ōtsutsuki. There, they all voiced their shared belief 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, Isobu 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. 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 Isobu, along with the other tailed beasts, from their prisons.

One-Tail Escort Arc
When Urashiki Ōtsutsuki began targeting Shukaku for its chakra, it was deduced he was interested in all the tailed beasts' chakra. Naruto organised a telepathic meeting with the other tailed beasts, except for Matatabi, Kokuō, and Chōmei, who each refused to accept aid from humans in fear of being captured and used again by them, despite their trust in Naruto, and thus decided to skip the meeting.

Kawaki Arc
In the anime, Isobu was gathered with the other tailed beasts as they sensed Kurama's chakra vanishing after it sacrificed its life in the battle against Isshiki Ōtsutsuki.

Video Games
Isobu is playable as Yagura's awakening in Naruto Shippūden: Ultimate Ninja Storm 3, Naruto Shippūden: Ultimate Ninja Storm Revolution and Naruto Shippūden: Ultimate Ninja Storm 4, and Rin Nohara's in the latter. Isobu also appears as a boss in Naruto Shippūden: Ninja Destiny 3.

Trivia

 * literally means 'beach stroker', and is also an adaptation of the name of the sea yōkai . The Isonade had a hooked tail, similar to Yagura's staff.
 * Since Rin died without having Isobu extracted, Isobu is the first known tailed beast to have "died" and revived.
 * In the Three-Tails' Appearance, Isobu's capture took place much later than in the manga, but played out in much the same way.