Ao

is a shinobi of Kirigakure, one of the two Kirigakure ninja selected to escort the Fifth Mizukage to the Kage summit.

Appearance
Ao is a middle aged man with an eye patch over his right eye, under which contains a Byakugan he took from a Hyuga clan member he defeated. He wears a talisman in each ear with the kanji for written on them twice on each side. He also wears a striped shirt and pants with seemingly the same pattern, with a robe over them. His 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.

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

After traveling for 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 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 kages have their meeting. When the Raikage crushes the table in a fit of anger, he along with the other attendants move to protect their leader, in his case the Fifth Mizukage. The commotion ends and the attendants return to their seats. Later while the kages are discussing the possibility of making Danzo the head of the alliance, Ao notices his chakra with his Byakugan; he then points out that Danzo 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 Danzo. When Danzo 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 Danzo. 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 Danzo tells them to stop. He later demands that Danzo and Fū stop whispering, revealing that he too can sense chakra, and knows that they have been located.

Abilities
At some point in the past Ao had a Byakugan from a defeated member of the Hyuga 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, Yagura. With it he was able to detect that Danzo had the right arm and eye of Shisui Uchiha transplanted into his body, and immediately recognized the chakra color emanating from those areas.

Ao seems to have an acute memory, as he remembered Shisui's color of chakra after one battle over eight years ago.

He, like Karin, Shi and Fū are able to sense other shinobi, and their chakra.

It is also notable that unlike a transplanted Sharingan, the Byakugan can be activated at will, rather than being in a constant release stage.

Trivia

 * means "blue" or "green".
 * There seems to be a running gag of when Ao scolds Chōjūrō, the Mizukage 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.
 * Ao, possessing the Byakugan, is one of four people to possess a kekkei genkai despite not being a member of the appropriate clan, the others being Kakashi Hatake, Tenzo, and Danzo.