In his professional debut as Aoiyama Kiyohito in the September 2009 tournament, he won the jonokuchi championship with a perfect 7–0 record.

He subsequently changed his name to Aoiyama Kōsuke for his jonidan debut in the following November tournament, which he also won with a 7–0 record followed by a playoff win against the sole Kazakhstani wrestler Kazafuzan.

Aoiyama responded to the less challenging schedule by producing a career-best performance in July 2017 – he entered the final day as the only wrestler left in a position to deny Hakuhō his 39th championship.

He was promoted to maegashira 2 but was forced to miss the first week of the September 2017 tournament due to a "bone contusion" in his left knee.

He scored 9–6 in this tournament, which was enough for an immediate return to makuuchi, albeit at the very bottom rank of maegashira 17 East.

In March 2019 he produced his second best score in the top division to date of 12–3, and won the Fighting Spirit Prize.

By March 2020 he had fallen to maegashira 13, but won eleven out of his first twelve matches to be the outright tournament leader on Day 12.

On his birthday, he declared that he had made efforts to control his weight, having lost 8 kg (18 lb), notably by consuming nimono.

In his Day 6 loss to Kotoshōhō, wrestling as Maegashira #14, Aoiyama was forced from the ring by oshidashi and landed favoring his right leg.

Following the September 2024 tournament, with demotion out of salaried status appearing likely, Aoiyama retired from professional competition.

[16] At his retirement press conference Aoiyama said he was glad he became a sumo wrestler, adding that his most memorable professional bout was against then-ōzeki Kotoshōgiku in July 2012.

He will remain with the Sumo Association as a coach under the elder name Iwatomo, which he had inherited following the passing of his stablemate, former maegashira Kimurayama, earlier in the year.

[17] Originally, Aoiyama was a yotsu-sumo specialist who preferred grabbing the opponent's mawashi and grappling rather than pushing or thrusting.

However, after gaining significant weight following his Makuuchi debut, he started to predominantly use pushing, thrusting and back-step pulling attacks as this had proven extremely effective due to his upper body strength.

The marriage was registered in August and the wedding reception was held in a Tokyo hotel in February 2017 with around 230 guests including fellow Dewanoumi group members such as Ura and Mitakeumi.

[23] Sanshō key: F=Fighting spirit; O=Outstanding performance; T=Technique     Also shown: ★=Kinboshi; P=Playoff(s) Divisions: Makuuchi — Jūryō — Makushita — Sandanme — Jonidan — Jonokuchi Aoiyama Kōsuke's official biography (English) at the Grand Sumo Homepage