Mū

was the of Iwagakure.

Background
During his life Mū was the teacher of Ōnoki, whom he taught how to use Dust Release. He also had a great enmity with the Second Mizukage. The two men eventually killed each other in battle.

Appearance
It appears that the entirety of Mū's body is covered by intricately wrapped bandages, with only his eyes and nose visible, giving him an overall mummy-like appearance. These features are accentuated by a dark-coloured headband with no distinguishing markings and dark pants. Due to the effects of the Summoning: Impure World Resurrection technique, he has black sclera and white irides.

When he was still alive, he donned what appeared to be a standard Iwagakure's flak jacket, with the village distinctive single sleeve on his left arm, and had two swords strapped to his back.

Personality
Mū is an extremely calm and collected individual, showing no signs of perturbation to his sudden resurrection. He's also unfailingly polite, taking his time to recount the previous events to the other Kage upon their forced summoning, and referring to the one whom he both killed and in turn was killed by with an honorific title, apparently bearing no ill-will towards him.

Despite the seeming civility displayed towards his fellow Kage, Mū has demonstrated that he first and foremost prioritises the prosperity of his own village regardless of the manner in which this affluence is achieved, even reminding his disciple to take full advantage of any post-war situation to assure the dominance of Iwagakure by quickly seizing control of the resultant spoils. This devious and merciless trait appears to be just one of the many reasons as to why the Second Mizukage despises him to such an extent.

Abilities
Having been the Kage of his village, Mū is an extremely powerful shinobi. He appears to be both extremely knowledgeable and analytical, being able to discern the exact method used to locate his position almost immediately after detection, seemingly without any prior information concerning the technique in question. While alive he carried a pair of what resembles swords wrapped up in bandages.

He is also a skilled sensor type shinobi displaying the ability to sense chakra over a distance of several kilometres, as well as to discern the similarity between the chakra belonging to close relatives such as Gaara and his father. Furthermore, when these detection capabilities are employed in conjunction with his quick reflexes, he can avoid techniques that even other Kage find difficult to evade, as demonstrated when only he instinctively managed to elude the clutches of Gaara's hands made from sand.

Invisibility
Mū is capable of becoming perfectly camouflaged with the surrounding environment. His camouflage is so good that he has become renowned as the, a title which he gained for seemingly having no form, and no chakra, while the technique was active. It is impossible to detect him by normal means. Mū considers anyone with the ability to sense his presence worthy of praise.

Nature Transformation
Mū is one of the few people capable of using a kekkei tōta, an advanced and extremely powerful form of kekkei genkai. In particular, he possesses the Dust Release, which allows him to combine the fire, the earth and the wind element to reduce his opponents to nothing more than mere dust, destroying them down to even a molecular level. Compared with fellow dust-user, Ōnoki, his power is implied to be on equal terms, as when the two initiated Dust Release: Detachment of the Primitive World Technique, the disastrous outcome although chaotic, demonstrated no evident victor in regards to strength. This may be due to the fact that Mū's power hadn't waned since his lifetime, a fact later affirmed by even Ōnoki.

This Dust Release makes him so powerful that the Allied Shinobi Forces fear him greatly, and Ōnoki only trusts himself to fight him, an assertion which Tsunade agrees with. Mū himself declares that sheer numbers alone do not matter in the face of his techniques, in spite of confronting nearly the entire Fourth Division at the time.

Shinobi World War Arc
Mū, as a former Kage, is resurrected alongside various other notable shinobi by Kabuto Yakushi, in preparation for the Fourth Great Shinobi War. When the Kage are mobilised, Mū is sent in the direction of the Fourth Division. As he approaches their location invisibly he is detected by Gaara's Sand Sensing technique, something which he commended his opponents for achieving.

Upon being noticed, Mū was forced to summon the Third Raikage, the Second Mizukage and the Fourth Kazekage. Recognising the means of their revival as the Impure World Resurrection, Mū searched for the Second Hokage, the technique's inventor and thus the presumed user, but informs his comrades that he could only pick up the presence of someone whose chakra signature was similar to the Fourth Kazekage's, and that that person is backed by a large army. The Fourth Kazekage then explained that the Second Hokage had been dead for many years, while also declaring that the one known as Orochimaru knew the deceased Hokage's technique as well. Mū later notifies the Second Mizukage that they're being controlled and thus, some of their movements are restricted, much to the latter and the Raikage's dismay.

Pursuing the division throughout the entirety of the night alongside the others, he discloses that their intended targets have been slowly retreating due to their indecision but that the opposition's movements have now altered, concluding their pursuit. When the Second Mizukage laments upon the prospect of confronting shinobi from his own respective village and curses the one responsible for resurrecting them, even Mū is in agreement. Shortly after, he detects the approach of two persons, who are preceded by Gaara's quicksand that descends upon the four in a colossal tidal wave. However, it isn't long until the Fourth Kazekage swiftly counteracts this through his Gold Dust. Upon this event, Gaara appears suspended above them and summons hands of sand to ensnare the Kage, with only Mū being able to escape captivity while sensing Ōnoki's presence, who appears to have lived a long life thanks in part to his master's teachings. Utilising the same technique to counteract that of his former disciple's, the attacks result in the formation of a huge crater in the middle of the battlefield, leading Ōnoki to assert that his predecessor's strength hadn't waned at all.

Suspecting a shinobi alliance had been formed, due to the accumulation of chakra types from different villages, Mū remains surprised that such a merger has occurred when it is later affirmed by Ōnoki. Informing his former disciple that only he can stop him, Mū then reminds Ōnoki that by taking full advantage of the post-war situation, the dominance of Iwagakure can be assured. Offending the Second Mizukage, the Third Raikage and most shockingly Ōnoki with such devious tactics, Mū immediately isolates himself when the battle resumes, pursued only by the latter.

Trivia

 * can mean nothingness or non-existence; possibly alluding to his ability to become invisible.