Ao was 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.[2] 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.
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 including Ao.
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.
Sensing System Barrier erection
Inoichi and Ao creating the Sensing Barrier.
Ao later assisted Inoichi Yamanaka 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.[4] 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.[9] 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.