Ao

is a shinobi of Kirigakure, one of the two Kirigakure ninja selected to escort the Fifth Mizukage to the Kage summit. He is also a skilled member of Hidden Mist ANBU's Hunter-nin squad.

Background
At some point in the past, Ao defeated an unknown Hyūga in battle. After winning, he took one of the Hyūga's eyes and implanted it into his right eye. He also fought Shisui Uchiha and, after the fight, he retained an acute memory of Shisui's color of chakra.

Appearance
Ao 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 once 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 bears a resemblance to that of Kisame Hoshigaki, while his attire is strikingly similar to that of Haku.

Personality
Ao believes that men should be tough and decisive, constantly scolding Chōjūrō for his pessimistic and weak demeanor. 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 behavior.

Abilities
As a member of Hidden Mist's hunter-nin, Ao is a highly capable tracker and has extensive knowledge of the human body. At some point in the past Ao had a Byakugan from a defeated member of the Hyūga clan transplanted into his right eye. 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 color 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 the hunter-nin of Kirigakure.

Ao seems to have an acute memory, as he remembered Shisui's color of chakra after one battle over eight years ago. Ao also seems to have very fast reflexes as he caught a kama seconds before it hit him and immediately threw it at his attacker.

Ao also seems to be a very skilled battler as in the past he was able to defeat a member of the Hyūga clan to take his eye and fight and survive against Shisui Uchiha, a talented member of the Uchiha clan.

Five Kage Summit arc
He was setting off with Chōjūrō to escort the Fifth Mizukage to the Five Kage meeting, called for by the Fourth Raikage. There he scolds Chōjūrō for his indecisiveness.

After traveling 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 jutsu 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 too can sense chakra, 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 Danzōs orders, tries to cut out Ao's eye. 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 jutsu.

Fourth Shinobi War arc
Ao later escorted Mei to a meeting of the leaders of the Allied Shinobi Forces.

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", and "call you ambitious" for "called off", and threatens to kill Ao if he doesn't shut up, much to his confusion.
 * Ao, possessing the Byakugan, is one of four people shown thus far to possess a kekkei genkai despite not being a member of the appropriate clan, the others being Kakashi Hatake, Yamato, and Danzō.
 * Of the four he is the only one that isn't from Konohagakure.
 * Ao and Haku have several similarities:
 * Both of them wear the same attire (possibly the hunter-nin uniform).
 * Both of their names are written in single kanji, which translate to a color.
 * Both of them possess a Kekkei Genkai (although Ao acquired his Byakugan via a battle, rather than inherit it genetically).
 * Ao killed a member of the Hyūga clan to obtain his Byakugan eye. Whether he killed a Main or Branch House member is unknown. 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.