Rōshi

was the jinchūriki of Son Gokū, the Four-Tails, that hailed from Iwagakure. The Four-Tails has been captured and sealed by Akatsuki, causing his death when the beast was extracted. However, upon his reincarnation, the Four-Tails was resealed within Rōshi.

Background
Rōshi became the jinchūriki of the Four-Tails over forty years before the Fourth Shinobi World War at a very young age. He left his home town of Iwagakure at some point to better understand and control the power of the beast within him.

Personality
Son Gokū mentioned that Rōshi was just as hard-headed as Ōnoki, the Third Tsuchikage, suggesting the two had been acquainted. Despite this, upon observing Naruto Uzumaki's battle against Obito and his Six Paths of Pain, as well as his knowledge of the tailed beasts final meeting with the Sage of the Six Paths, he came to regrettably believe that all the jinchūriki could have walked down the right path if they were more like the young man. Also despite being Son's jinchūriki for over forty years, he never referred to the beast by its true name, stating that he had not become soft-hearted enough to do such a thing. Before Son was resealed into the Demonic Statue of the Outer Path, he revealed to the beast that he never forgot its name, making peace with the giant ape.

Appearance
Rōshi had red hair, moustache and beard which tapered off to a point. He was shown wearing a large headpiece consisting of a three pointed crown-like ridge, bearing both his Iwagakure forehead protector, a ring, and a prominent black piece of armour running across his cheeks and the bridge of his nose. He wore a long-sleeved light-red shirt and pants, with mesh-armour shirt and fitted black suit underneath, along with calf-length sandals. Around his waist he wore a brown sash-like high-waist piece with a pouch in the front and armoured lapels falling to the sides. Interestingly, his headpiece, hair and beard seemed to model his tailed beast's.

Abilities
He has been noted to be a very powerful shinobi. Kisame, a powerful Akatsuki member himself, stated that he was not one to play around with as he was a tough one to capture. He was also seen using a curved kunai with which it can be assumed that he had proficiency wielding.

After his reincarnation and serving as one of Tobi's Six Paths of Pain, Rōshi is seen with both the Sharingan and Rinnegan. Combining the perceptual and predictive abilities of the former with the shared field of vision ability of the latter, allowed Rōshi to use his attacks in a more precise and coordinated fashion as well as react to enemy attacks more efficiently, both individually and in conjunction and with the other jinchūriki.

Nature Transformation
By borrowing the Four-Tails' power, Rōshi was able to use its Lava Release ninjutsu, created through simultaneous use of fire and earth-based chakra, to create a torrent of lava that can melt almost anything. In the anime, Tobi referred to him as, further indicating his prowess with it. He could create a giant geyser of lava as seen in the anime or spit multiple balls of lava at the enemy. He could also create an armour made of lava that not only has defensive purposes but adds lava to his taijutsu attacks increasing their potential damage.

Jinchūriki Transformations
As the Four-Tails' jinchūriki, Rōshi is granted a significant amount of chakra and stamina from the beast. The full extent of his control is unknown, but he could form at least one of the beast's tails upon his reincarnation, further enhancing his power and strength. After being immobilised by B's clone, he transforms into his Version 2 form, in this form he was able to create an enormous torrent of lava, scorching the Eight-Tails. When Rōshi attacked Naruto and Killer B, Tobi forced him to transform into his full Four-Tails form. In this form, he displayed tremendous strength, being able to toss Killer B in his full Eight-Tails form a considerable distance away.

Itachi Pursuit Arc
After an unseen and difficult battle with Kisame Hoshigaki of Akatsuki, Rōshi was somehow defeated and captured by Kisame. He later died as the result of having the Four-Tails extracted from his body.

Shinobi World War Arc
In preparation for the Fourth Shinobi World War, Rōshi was reincarnated by Kabuto Yakushi to fight against the Allied Shinobi Forces, before being mobilised alongside the other deceased jinchūriki.

As dawn broke on the second day of war, it was revealed that Tobi had turned the reincarnated jinchūriki into his own customised Six Paths of Pain, with each having a Rinnegan and Sharingan in place of their left and right eyes respectively. Each jinchūriki also had their particular tailed beast resealed within them and a chakra receiver embedded into their bodies.

Rōshi later travelled together with Tobi, in pursuit of Naruto and Killer B. Encountering their targets, the reincarnated jinchūriki were sent into battle with Rōshi leading the offensive, using his Lava Release: Scorching Stream Rock Technique to pressure the enemy. When this initial assault failed, he, like the others, unleashed the power of their respective tailed beast by materialising the first of its tails.

Whilst Naruto and B conversed, Rōshi exploited this opportunity to attack the former directly, after covering his body in lava. Despite evading the strike, Naruto's face was still scorched by the heat, but when Rōshi attacked again, Naruto endured the blow in an attempt to destroy the chakra receiver embedded in Rōshih's chest. However, this was thwarted by Han. Incapacitated in the wake of the Eight-Tails' devastating attack, after B's recent transformation, Rōshi was then restrained by the latter's sealing technique. However, before the technique's completion, he managed to escape by adopting his Version 2 form, where he then proceeded to burn the Eight-Tails.

Regrouping with the other reincarnated jinchūriki, after Kakashi Hatake and Might Guy's intervention, Rōshi charged past the pair towards Naruto and B. When he clashes with the former, Tobi forcefully transformed him into his full Four-Tails form, where he then proceeded to assault the Eight-Tails. Grabbing one of the beast's tails, Rōshi hurled the two jinchūriki upwards and, after dislodging Naruto in the process, prepared to swallow him. However, despite Naruto's efforts to lodge himself between the beast's jaws, and B's attempts to restrain the ape, the former is ultimately swallowed whole.

While Naruto conversed subconsciously with Son Gokū, Rōshi resisted B's efforts to free his captive comrade, only to be forced to eject Naruto when the young man multiplied. He then tried to impede Naruto from removing the chakra receiver embedded in the beast's chest, but failed to do so thanks to a coordinated strike, leaving Rōshi's incapacitated body behind as Son Gokū was resealed into the Demonic Statue of the Outer Path.

When a transformed Naruto's Tailed Beast Ball later clashed with the collaborative one formed by the other tailed beasts, Rōshi's unconscious body was protected by the Eight-Tails from the resulting blast. Afterwards, Naruto subconsciously met with the other beasts and their jinchūriki, where it was revealed that shortly before Son was resealed, Rōshi questioned his beast as to whether it thought they too had taken the wrong path during life. He then stated that despite not being considerate enough to have spoken it, he had not forgotten the beast's real name. As the two fade away, a smiling Rōshi asked the beast if calling it "Son" would be all right.

After Son was resealed into the Demonic Statue of the Outer Path, Rōshi and the other jinchūriki's corpses were collected by B and held in the Eight-Tails' tentacles. With the release of the Impure World Reincarnation, Rōshi and the others are enveloped in a light of sorts before their bodies start to deconstruct and Rōshi's soul returned to the afterlife.

Trivia

 * means "old age" or "elderly". means "purple". It is possible Rōshi was named after the Dragon Ball character Master Rōshi, considering that the Four-Tails' design was also inspired by Dragon Ball.
 * In order to prevent the jinchūriki from turning traitor, it is tradition for the host to be selected from the family of the village's own Kage. It might be that Rōshi somehow was connected with one of the Tsuchikage.
 * In the manga Rōshi's headpiece is depicted as having a golden ring on the left side. The golden ring on Rōshi's headpiece was not present in the anime. This was later added as of episode 256.