Mū

was the of Iwagakure During his lifetime, Mū was renowned as the  due to his ability of having neither a physical form nor detectable chakra.

Background
Before becoming the Second Tsuchikage, he accompanied the First Tsuchikage to the first ever Five Kage Summit. There he stood behind the First watching diligently as the proceedings unfolded.

During his lifetime, Mū taught Ōnoki how to use Dust Release. At some point in time, both he and Ōnoki met with Madara Uchiha, after an alliance had been formed between their respective villages. Despite their standing, Madara boldly declared that Konohagakure would remain the dominant power and as such, they should obey any orders given. This culminated in both parties engaging in battle where Mū and Ōnoki were defeated. It was during Mū's era when Iwagakure began to actively try to acquire other tailed beasts, having the Four-Tails and the Five-Tails already in its possession.

He also had a great enmity with the Second Mizukage and the two men eventually killed each other in what would be their final confrontation.

Personality
Mū was an extremely calm and collected individual, showing no signs of perturbation to his sudden reincarnation. 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 killed and in turn was killed by with an honourific title, apparently bearing no ill-will towards him. In the anime, Mū was angrier at the Second Mizukage, even grabbing him by the collar of his coat and threatened to kill him. Despite his respectful attitude, Mū is shown to be highly deceptive, twisting facts and leaving out key information just to boast about himself and put down others. An example of this was when he reminded Gengetsu he killed him, leaving out the fact Gengetsu also killed 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. Even seconds before his sealing he attempted to warn Ōnoki to take precaution. This devious and somewhat merciless trait appears to be just one of the many reasons as to why the Second Mizukage despises him to such an extent. This under-handed tactic would later be taught to his student, which would become the reason for Iwa's bad reputation among the Five Great Shinobi Countries. However, in the anime, just before his soul returned to the afterlife, Mū had a change of heart and acknowledged that Ōnoki must secure the future of the Allied Shinobi Forces.

Despite Mū's views on alliances, he still attempted to help the Allied Shinobi Forces any way he could, even while being controlled. Right as one of his halves was sealed he attempted to warn Ōnoki he had split, but his message failed to reach his successor.

Appearance
Mū's entire body was covered by intricately wrapped (dark grey in manga, seaweed green in the anime) bandages, with only his violet-coloured eyes and nose being visible, giving him an overall mummy-like appearance. Along with this Mū wears a black headband (dark blue in the anime) with no distinguishing markings and a pair of black pants. He also doesn't wear shoes as his feet are also bandaged heavily. Due to the effects of the Summoning: Impure World Reincarnation technique, he has black sclerae and white irides after Kabuto Yakushi eradicates his personality.

When he was still alive, Mū was shown to have donned what appeared to be a standard Iwagakure's flak jacket and forehead protector, with the village distinctive single sleeve outfit over his left arm. He also carried two swords strapped to his back which had slender handles which were also bandaged. At the time of the first Kage Summit, where he accompanied the First Tsuchikage, Mū seemed to have worn a casual kimono.

Abilities
As the Second Tsuchikage, Mū was an immensely powerful shinobi, such that he was able to kill the Second Mizukage — albeit at the cost of his own life. Prior to becoming Tsuchikage, he was chosen to be the bodyguard of his predecessor. His abilities even compelled the Allied Shinobi Forces leaders to summon Ōnoki on the battlefield as the only way to stop him. Mū himself declared that sheer numbers alone do not matter because of the nature of his techniques, despite confronting nearly the entire Fourth Division at the time.

Sensory Perception
Mū was a skilled sensor-type shinobi, having displayed the ability to sense chakra over a distance of several kilometres. He could also discern the similarity between of chakra signatures belonging to close relatives, and distinguish chakra from different populations. Furthermore, when these detection capabilities were employed in conjunction with his quick reflexes, he could avoid techniques that even other Kage found difficult to evade, even from his blind-side.

Ninjutsu
Mū was able to split himself into two duplicates to help escape a lethal blow, but at the cost of reducing his power by half. He was also physically strong enough to lift massive rocks off of his body, even with only half of his power. It was impossible to detect him by normal means. While alive, Mū was seen carrying a pair of swords, implying that he was also skilled in kenjutsu.

Nature Transformation
Mū was one of the few shinobi in history who could wield all five elemental nature transformations. He is also one of the few capable of utilising a kekkei tōta, an advanced and extremely powerful form of kekkei genkai. In particular, he possesses the Dust Release, which allows him to combine fire, earth, and wind natures to reduce his opponents to nothing more than mere dust, destroying them down to even a molecular level. While Mū was in his split state, he was not able to use Dust Release techniques due to his power being halved.

With Earth Release, Mū could make his body light enough for flight. He was also capable of completely hiding his presence through the use of Water Release. His camouflaging ability was so great, he became renowned as the, a title which he gained for having neither a physical form nor detectable chakra while the technique was active. Mū could also use Yang Release.

Intelligence
Mū appeared 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. He also apparently deciphered the mechanisms behind his rival's Steaming Danger Tyranny and passed on the information to his student, as was later speculated by the Second Mizukage himself.

Fourth Shinobi World War: Confrontation
In preparation for the Fourth Shinobi World War, Mū was reincarnated by Kabuto Yakushi alongside three other deceased Kage to fight against the Allied Shinobi Forces. When they were mobilised, Mū was sent in the direction of the Fourth Division but despite being invisible as he approached their location, he was detected by Gaara — a feat which he commended as he was forced to summon the Third Raikage, the Second Mizukage and the Fourth Kazekage. After a brief argument with the Mizukage over the manner of their deaths, Mū noted the means of their reincarnation, and searched for Tobirama Senju, believing him to responsible for their return before informing his fellow Kage that he could only pick up the presence of someone whose chakra signature was similar to that of the Fourth Kazekage's and that, that person was backed by a large army. The Kazekage then explained that Tobirama had been dead for many years during his lifetime and that he knows another who can use the deceased Hokage's technique as well. Mū and the other Kage pursued the division throughout the night, forcing their opisition into a slow retreat until cornering them.

He then detected two individuals approaching, who are preceded by a colossal wave of sand that bore down on the Kage, but the Fourth Kazekage swiftly counteracted this with his Gold Dust. At this point, Gaara appeared suspended above them and sculpted hands of sand to ensnare the Kage, with only Mū able to escape captivity while sensing Ōnoki's presence above them. Greeting his old pupil he noted that Ōnoki had lived a long life thanks in part to him passing down his teachings to him. Utilising the same technique to repel that of his former disciple, the converging attacks resulted in a huge crater in the middle of the battlefield, leading Ōnoki to assert that his predecessor's strength hadn't waned. Suspecting a shinobi alliance had been formed due to the accumulation of chakra types from different villages, Mū was even more surprised that such a merger has occurred when it was confirmed and even more so that Ōnoki had joined it. Informing his former disciple that only he could stop him, Mū reminded Ōnoki that by taking full advantage of the post-war situation, the dominance of Iwagakure could be assured. Offending the Mizukage, the Raikage and most shockingly Ōnoki with such devious tactics, Mū immediately isolated himself when the battle resumed, pursued only by his student.

As the chase concluded after the pair had seemingly clashed several times, Mū declared to an exhausted Ōnoki, that his age had caught up to him and as he disappeared from view, and told him to call Gaara before he died as well. However, telling Mū not to underestimate him just yet, Ōnoki creates several rock clones. As their battle ensues, Mū took Ōnoki by surprise from behind in mid-air, but with Gaara's timely arrival and warning, Ōnoki managed to avoid the blow but threw his back out in the process. As Mū prepared to attack them with his Dust Release, Naruto Uzumaki attempted an surprise attack with his Planetary Rasengan technique, but, sensing the attack, Mū easily evaded it. Believing his technique to be the faster of the two, only the combined efforts of both Gaara and Naruto ensure that the latter lands a hit on a shocked Mū, which sent him hurtling through a nearby rocky outcrop. Colliding with the ground below, Ōnoki swiftly moved in and weighed Mū's body down, which prevented him from moving.

As Mū was being sealed within Gaara's sand, he told Ōnoki that for someone who detested other villages, he worked well with them, to which Ōnoki replied that he had lived long enough to experience such a change. Just as the seal neared its completion, Mū attempted to warn them but was sealed in full before he could finish his sentence. The warning was revealed when Mū emerged from the rubble left in the wake of Naruto's devastating attack. Chastising his former disciple's naivety as his wounds heal, Mū reveals that he split his body into two while it was obscured by the prior attack. Unable to remove the seal so he could reunite with his other half, Mū was made to begin summoning "that" reincarnation. Due to his weakened state, it took longer for Mū to complete the summoning. In the anime, it took so much time, Kabuto was required to summon various additional reincarnations to stall.

Fourth Shinobi World War: Climax
Eventually, Mū completed the Summoning Technique. Narrowly avoiding the summoned coffin's lid after it was violently blown off, Mū was shocked at the figure who emerged, remarking that the individual behind their reincarnation must have a good understanding of war to summon such a person. Together the pair walked towards Gaara and the Fourth Division, where it was revealed that the one Mū summoned was Madara Uchiha. When Madara noted that all of the shinobi were wearing similarly marked forehead protectors, Mū informed him that an alliance had been formed in response to the on-going war. As Mū was unable to answer Madara's question about who was controlling them, Kabuto overrode Mū's consciousness and used him to talk directly with Madara. As the battle restarted, Mū narrowly avoided Gaara's attack, and attempted to form a Dust Release technique, but it soon dispersed due to his power in his split state. Observing the ensuing conflict, Kabuto continued to speak through Mū's where he remarked upon Madara's demonstration of the Rinnegan and its power, even after the impact of two enormous meteorites.

Reforming in the wake of the collision, Kabuto had Mū approach the few remaining survivors of the Alliance, whilst providing Madara with a detailed overview of current affairs. However, when the two resumed their attack, they are repelled by Tsunade and A who had just been transported to the battlefield. Recovering from A's punch, As Mei created a thick mist, obscuring the battlefield, Kabuto positioned Mū right in front of Madara but he was easily knocked away by a lightened A. Afterwards, Mū was pursued by Dodai and the Hokage Guard Platoon. Once recovered, Mū continued to elude his pursuers under Kabuto's direction, as the battle between Madara and the Kage intensified. Later, with the Impure World Reincarnation being released, Mū's consciousness returns to him but only for a short while as he was enveloped in a light of sorts and began deconstructing, much to his shock, regaining his consciousness only mere moments before starting to break down and his soul returned to the afterlife. In the anime, before his soul ascends, Mū told his opponents to tell Ōnoki that he must protect the future of the Shinobi Alliance and only then can he come and tell him all about it.

Kaguya Ōtsutsuki Strikes
Subsequent to Kaguya Ōtsutsuki being sealed by Naruto Uzumaki and Sasuke Uchiha, he and the other deceased Kage were summoned from the Pure Land by Hagoromo Ōtsutsuki to aid him and the Hokage in summoning Team 7, the tailed beasts and Madara from Kaguya's dimension. Later, his and the other Kage's souls were returned to the Pure Land.

Trivia

 * can mean "nothingness" or "non-existence", possibly alluding to his ability to become invisible.
 * His combination of bandage-covering and the technique he uses may be referring to Griffin, the main character of "The Invisible Man" novel of H.G. Wells.
 * Despite Mū being noted to use the Dustless Bewildering Cover, which is stated to manipulate water, he is not listed as a Water Release user in the fourth databook.

Quotes

 * (To Ōnoki) "After the conflict ends, an alliance becomes squabble over spoils of war. The victor there becomes the new dominant power."
 * (Before returning to the afterlife) "Tell Ōnoki he must secure the future of the Allied Shinobi Forces. Only then can he come and tell me about it."