Ao

is a shinobi from Kirigakure and a member of his country's ANBU Hunter-nin squad.

Background
Ao is an experienced veteran, having been raised under the feared regime of the Bloody Mist and having fought in war, even before the advent of the Fourth Shinobi World War. He has clashed several times with Konoha shinobi. At one point he defeated an unknown Hyūga, taking one of the Hyūga's Byakugan and implanting it into his own right eye socket. Later, he had a confrontation with Shisui Uchiha, which left enough of an impact on Ao for him to clearly remember Shisui's abilities and his chakra colour long after the event.

Appearance
He is a middle aged man with a patch over his right eye, under which he hides a Byakugan he took from a Hyūga clan member he defeated. He wears a talisman in each ear with the kanji for written on them twice on each side. These talismans react when his Byakugan is under threat and will protect it from anyone, even himself. He also wears a striped shirt and pants with seemingly the same pattern, with a green robe over them. His blue hair is styled in a manner similar to that of Kisame Hoshigaki. He normally wears a bluish-green kimono and a striped under-shirt.

With the outbreak of the Fourth Shinobi World War he has taken to wearing the standard outfit of the shinobi alliance with a Kirigakure flak jacket over it.

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

Abilities
As a veteran of Kirigakure's hunter-nin, Ao is a highly capable tracker and has extensive knowledge of the human body. He seems 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, with great skill. He is 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.

Sensor
He is also a highly skilled sensor shinobi, a testament to which is that during the Fourth Great 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 resurrected shinobi out of thousands of White Zetsu clones a feat that his counterparts could not perform. Along with Inoichi, 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.

Byakugan
At some point in the past, Ao took a Byakugan from a defeated member of the Hyūga clan and transplanted into his right eye socket. His skill with it is notable, as he said that his eye saw through the illusion placed on the Fourth Mizukage. With it he was able to detect that Danzō had the right arm and eye of Shisui Uchiha transplanted into his body, and immediately recognized the chakra based on the colour emanating from those areas. It is also notable that unlike a transplanted Sharingan, the Byakugan can be activated at will, rather than being in a constant release stage. The Byakugan is protected by the talisman seals that Ao wears as earrings, and will cover the eye if anyone tries to take it. The seal cannot be deactivated by anyone (not even the Mizukage) except Ao himself or other Hunter-nin.

Five Kage Summit Arc
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 the head of the alliance, Ao notices his chakra with his Byakugan; he then points out that Danzō confiscated his Sharingan and arm 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 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.

Confining the Jinchūriki Arc
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.

Shinobi World War Arc
Ao was appointed captain of the Sensor Division of the Allied Shinobi Forces. Ao and Inoichi Yamanaka were later seen working together to create a barrier.

Ao later states the fact 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 resurrected 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 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.

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.

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.
 * Ao killed a member of the Hyūga clan to obtain his Byakugan eye, but it is unknown whether he killed a Main or Branch House member. 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.