Ao

was an Anbu of Kirigakure's Hunter-nin Corps.

Background
During the Third Shinobi World War, he defeated a Hyūga member and took one of their Byakugan, which he implanted into his right eye socket. With it, he saw through the illusion placed on the Fourth Mizukage. Years after the war, he encountered Shisui Uchiha, which left enough of an impact on Ao for him to clearly remember Shisui's abilities and his chakra colour.

In the anime, shortly after Yagura's passing and Mei Terumī was made the Fifth Mizukage, Ao was present when the village received an invitation from Konohagakure and Sunagakure to join an impromptu Chūnin Exams they would be hosting together. Ao noted that as the village was still recovering from Fourth's passing and thus shouldn't waste time on an event seemingly designed to promote Gaara as the new Kazekage. After Mei threatened Ao's life after misinterpreting his words as an insult to her marital status, it was ultimately decided the Kiri-nin would not take part in this event.

Personality
Ao was calm, prideful, stern and was the epitome of a stereotypical masculine individual. He believed that men should be tough and decisive, constantly scolding Chōjūrō for his pessimistic and weak demeanour. This attitude seemed to be caused by his upbringing during the times when Kirigakure was known as the "Village of the Bloody Mist". He had a tendency of bringing up how things were done during those days, usually while fussing over Chōjūrō's behaviour. Despite his fussing, Ao did seem to have some type of friendship with Chōjūrō as he offered to treat him to a meal for luck in the upcoming war.

Appearance
He was a middle aged man with blue hair which is styled in a moused-up manner. His left eye was blue and his right eye was covered with an eye-patch, under which he concealed the Byakugan that he obtained from a Hyūga clan member he defeated. He wore a talisman in each ear with the kanji for a humble form of written on them twice on each side. These talismans reacted when his Byakugan is under threat and will protect it from anyone, even himself. He also wore the standard striped, grey suit, with a green haori that had white trimmings that stop halfway down, over them.

With the outbreak of the Fourth Shinobi World War, he donned the standard outfit of the shinobi alliance with a Kirigakure flak jacket over it.

Abilities
As a veteran of Kirigakure's hunter-nin, Ao was a highly capable tracker and has extensive knowledge of the human body. He seemed to possess a great deal of speed and agility, being able to grab a kama thrown at him just moments before it slashed his neck, in turn throwing the weapon and hitting the assailant, who had moved to assault him from the back, all in quick sucession. He was also clearly a very skilled combatant, as he was capable of defeating a member of the Hyūga clan and surviving a fight with Shisui Uchiha, a feared shinobi who was regarded as a genius even amongst the Uchiha.

Sensory Perception
He was also a highly skilled sensor shinobi, a testament to which is that during the Fourth Shinobi World War he was appointed as the Captain of the Sensor Division of the Allied Shinobi Forces. With his sensory skills he could even pick out the reincarnated shinobi out of thousands of White Zetsu clones, a feat that his counterparts could not perform. Along with Inoichi Yamanaka, he was able to erect an immense Sensing Barrier, which allowed him to monitor the battle between the Allied Shinobi Forces and the White Zetsu Army. Ao counts among the few sensors that have shown the ability to sense natural energy.

Byakugan
Ao possessed a single Byakugan that he could activate at will, which he transplanted from a Hyūga clan member he defeated. The Byakugan was protected by the talisman seals that Ao wore as earrings, and would cover the eye if anyone tried to take or attack it. Once activated, the seal could only be deactivated by a hunter-nin like himself. With it, he could determine if an individual was under the influence of genjutsu and distinguish chakra colours of certain individuals.

Five Kage Summit
Ao sets off with Chōjūrō to escort the Fifth Mizukage to the Five Kage Summit, called for by the Fourth Raikage. There he scolds Chōjūrō for his indecisiveness. After travelling for some time, the small group stopped at an inn to eat and rest. After being told that the Fourth Mizukage's teachings are to be forgotten, by both the Fifth Mizukage and Chōjūrō, he yells at the latter for not being able to make up his mind as to what to order for dinner and sends him to get food.

After arriving at the summit in the Land of Iron, Ao sits behind the Kiri curtain listening as the Kage have their meeting. When the Fourth Raikage crushes the table in a fit of anger, Ao, along with the other attendants, move to protect their respective Kage. The commotion ends and the attendants return to their seats. Later while the Kage are discussing the possibility of making Danzō Shimura the head of the alliance, Ao notices his chakra with his Byakugan; he then points out that Danzō confiscated his Sharingan from Shisui Uchiha, someone he'd fought in the past. Before he can prove the accusation, Zetsu appears and Ao moves to defend the Mizukage. After the Raikage seemingly kills white Zetsu, he tells Ao to watch Danzō. When Danzō states that he cannot use the mind controlling technique that many times in one day, Ao says that he is unsure if he's lying and that he can no longer trust Danzō.

When Fū Yamanaka and Torune try to go and battle Sasuke, Ao tells them to stay right there as the Raikage told him to watch over them and when they get into battle position Danzō tells them to stop. He later demands that Danzō and Fū stop whispering, revealing that he's also a sensor and knows that they have been located. When Sasuke finally reaches the meeting room, Ao is the first to notice his presence. When Sasuke is attacked, Ao and Karin simultaneously notice that Danzō is attempting to escape. Ao asks permission to follow, and is told not to follow him too far. He begins his pursuit after telling the Mizukage he would leave the Akatsuki (Sasuke and his comrades) to her. Sasuke attempts to follow with Karin in tow, but is promptly stopped by the Mizukage.

On his way, Ao is also trapped by Zetsu's Spore Technique, but he manages to get free from it; only to be suddenly trapped by Fū's Mind Puppet Switch Cursed Seal Technique. Fū, following Danzō's orders, tries to retrieve the Byakugan. However, Ao tells Fū that there is a special seal in his eyes, making it impossible for enemies to try to take his eye. As Fū decided to improvise by making Ao decapitate himself, Ao warned Fū to time it carefully as too soon would allow Ao to dodge and too late would take Fū down as well. Before the true outcome could happen, the Mizukage and Chōjūrō arrive and save Ao. Fū, still in control of Ao, tried to trick the Mizukage into removing the seal on his eye, but she saw through Fū's deception when he acted kindly to Chōjūrō's insult. The Mizukage then punches Ao in the face for calling her an old hag, unaware that Fū already ended the technique.

As they are arriving back in Kirigakure, the three are informed that the Water Daimyō had approved the alliance. Ao is later relieved that former Kirigakure shinobi Kisame Hoshigaki had fallen to the hands of Killer B, not having to worry about any future conflicts. As a sign of good luck, he insists that once they settle down that he treat Chōjūrō to a meal before the upcoming war. When he is rejected, he chides him for his dislike of oily foods and to keep it up if he wanted to "fail at the crucial moment". He is later seen ordering Kirigakure shinobi to gather all ninja tools currently available to them in preparation for the war.

Fourth Shinobi World War: Countdown
Ao later escorted Mei to a meeting of the leaders of the Allied Shinobi Forces. He was also seen at the alliance's headquarters making preparations along with the other shinobi.

Fourth Shinobi World War: Confrontation
Ao was appointed captain of the Sensor Division of the Allied Shinobi Forces. When he met with his division, he told a perturbed C who was participating in war for the first time in his life, that a great deal depended on how well they did their job as they were the eyes of the Alliance.

Ao later assisted Inoichi in creating the barrier which the Sensor Division would be using. When the war officially breaks out, he notes that if it had not been for Muta Aburame's information they would have had no idea that the enemy were travelling underground. He then tells his division members to shift the barrier downwards to pick up on the enemy's exact location. Upon hearing of the large amount of enemy forces heading towards the First Division, Ao uses his sensory abilities to hone in on the revived shinobi on the battlefield while the others maintaining the barrier focused on the large scale sensing. Ao discovered that they were many reincarnated shinobi amongst the troop all of which were infamously strong during their lifetimes. He then reports that there are two persons on the battlefield with immense chakra reserves tinged with the chakra of the Nine-Tailed Demon Fox. They were later identified as Kumogakure's Gold and Silver Brothers.

Later after the Demonic Statue of the Outer Path is summoned to the battlefield, Ao senses it and identifies it as a "gargantuan mass of chakra". He wonders to himself what they were up against. As night falls and the Alliance is thrown into turmoil from the reports of spies who had entered their ranks and were murdering the shinobi forces, Shikaku surmises that the enemy might be using some sort of illusion on the shinobi to cause them to act this way, Ao states that Itachi Uchiha was the only person with the kind of prowess to even take control of someone outside the range of their sensors, but also states that even for him it'd be impossible to be controlling so many persons at once. He then looks to Shikaku for orders telling them that if they didn't come up with something they'd end up having their own shinobi killing each other.

Fourth Shinobi World War: Climax
Though after hearing the progress of the battles from Inoichi leads to some celebration. Ao cuts it short after detecting a new presence on the battlefield near Gaara's division. After a tremor is felt at headquarters, Ao reports that a huge number of shinobi from the Fourth Division had been killed all at once.

Reporting on the battle between Tobi, Naruto and B, Ao tells headquarters that B had seemingly transformed into his full Eight-Tails form but was still being pressured. As the Nine-Tails' chakra is released, Ao and the other sensors manning the barrier comment on the sheer power. Thinking to himself, he states that it felt somewhat different because there was something else that he could feel. He then reports to Shikaku the situation on the battlefield, telling him that the four men there were actually beating the "masked Madara". Later, when the Sensing Water Sphere in HQ became distorted, Ao hastily followed through with Shikaku's order to check out the situation.

In shock of the still-displaced Sensing Water Sphere, he alerts everyone in HQ to the fact that the Ten-Tails had changed its form another time, and then wondered why the beast was firing off Tailed Beast Balls in far-off directions. Realising the direction of the fourth attack, Ao confirmed Shikaku's suspicions that the attack was headed towards the HQ. With this, Ao and the others resolved to perform the duties they were assigned until the end, and were able to relay one last strategy before the attack reached HQ, destroying the building and killing everyone inside, including Ao.

Video Games
In Naruto Shippūden: Ultimate Ninja Storm Generations, Naruto Shippūden: Ultimate Ninja Storm 3 and Naruto Shippūden: Ultimate Ninja Storm Revolution, Ao is a support-only character.

Creation and Conception
When designing Ao, Kishimoto wanted to create a character with an air of severity and masculinity while still seeming tranquil. His eye-patch is supposed to convey masculine trendiness, and his haori is to serve a dual purpose in that it should convey his quiet and mature personality while the sleeves were to signify that Ao was not a close-range fighter. Kishimoto also noted that he deliberately made Ao's attire similar to Haku's and was even going to go as far as to have him wear a mask, but ultimately decided against it.

Trivia

 * means "blue" or "green".
 * There seems to be a running gag of when Ao scolds Chōjūrō, Mei always mishears it as something offensive towards her love life, such as "arrangements" for "engagements", "manage" for "marriage", and "call you ambitious" for "called off", and threatens to kill Ao if he doesn't shut up, much to his confusion.
 * It's unknown whether he killed a Main or branch house member of the Hyūga clan that he obtained his Byakugan from. It is however likely that he killed a member of the main house or he removed the eye of a Branch member while his opponent was still alive; whether the Hyūga seal prevents this is unknown.