However, interested in modalities like Kosen Judo which were away from him due to the Kodokan competition rules, he moved to other combat sports, until landing in mixed martial arts.

One of the key influences that shifted Aoki to mixed martial arts was watching Kazushi Sakuraba defeat powerful foreign players in Pride FC.

He earned both his A-class Shooto rank as well as his Brazilian Jiu-Jitsu black belt under Nakai, and became one of the team's main teachers.

He later would show further unorthodox grappling skills against veteran Seichi Ikemoto and Keith Wisniewski, who he defeated by breaking his arm with a standing wakigatame also known as a Fujiwara armbar.

[10] Afterwards, Melendez was shown in the crowd with a sling, and announced he would like to face Aoki at Pride Shockwave 2006 on New Year's Eve.

Originally, his opponent was to be two-time K-1 Hero's Middleweight Grand Prix champion Gesias "JZ Calvan" Cavalcante.

Here Aoki finally faced Cavalcante on March 15, 2008, at the opening round of the Dream Lightweight Grand Prix tournament.

Early in the first round, the referee stopped the action when Cavalcante apparently landed illegal elbow strikes to the back of Aoki's neck.

Joachim Hansen took his place and defeated Aoki by TKO (punches) at 4:19 round 1 to become the first Dream Lightweight Champion.

[24] Aoki started quickly, securing Alvarez's back after catching a kick, before being thrown to the canvas by the stronger American.

Aoki met Fedor Emelianenko during a five-minute "special exhibition" at an April 29 M-1 Challenge (presented by Affliction) event in Tokyo.

Aoki ended up defeating Hansen in the second round for the title shot via submission (armbar) to become the new DREAM Lightweight Champion.

[32] On December 22, 2009, it was announced that Aoki would not be taking on fellow DREAM fighter Tatsuya Kawajiri, but would be fighting Sengoku Lightweight Champion, Mizuto Hirota.

[33] In his pre-fight interview Aoki stated that he felt insulted with the short notice changes as he was looking forward to battling it out with one of the world's other top lightweight competitors in Kawajiri.

The fight between Aoki and Hirota was considered to be one of the main events of the night along with Satoshi Ishii vs. Hidehiko Yoshida and the K-1 bout Masato vs Andy Souwer.

After Aoki's defeat to Gilbert Melendez in Strikeforce he has expressed interest to train at Cesar Gracie's camp in northern California.

[37] Aoki successfully defended his Lightweight title against top contender Tatsuya Kawajiri in just under two minutes of the first round via an Achilles lock submission, at Dream 15 on July 10, 2010.

The commentary team of Michael Schiavello and Frank Trigg were openly criticising Aoki for his rule breaking during the first round, while the Japanese crowd uncharacteristically booed him.

At 0:04 of the second MMA rules round, Aoki was knocked out immediately as he went for a double leg takedown via flying knee and subsequent grounded strikes.

[43] Aoki then defeated Lyle Beerbohm on April 9, 2011, at Strikeforce: Diaz vs. Daley via neck crank in the first round.

[49] Aoki fought Satoru Kitaoka for the DREAM lightweight title at Fight For Japan: Genki Desu Ka Omisoka 2011.

Aoki defeated his opponent at 2:01 of the second round via rear-naked choke,[57] successfully avenging his Evolve teammate Zorobabel Moreira.

[69] Aoki faced Ev Ting on October 6, 2018, at ONE: Kingdom of Heroes and won the fight via arm-triangle choke in the opening minute of the bout.

Due to the victory, Aoki secured a fight for the vacant lightweight championship against the winner of Eduard Folayang and Amir Khan in the promotion's inaugural event in Tokyo, Japan on March 31, 2019.

[75] Aoki faced James Nakashima on January 22, 2021, at ONE Championship: Unbreakable[76] He won the fight via submission in the first round.

[102] Aoki has received criticisms by the mixed martial arts community for his disrespectful victory celebrations and perceived lack of care for his opponents, often causing injuries which are seen as needless.

He firstly became known for breaking Keith Wisniewski's arm by waki-gatame,[7] then doing the same with Kuniyoshi Hironaka via flying armbar in a submission grappling match, sidelining him for a year.

After Aoki won by breaking Hirota's arm in a brutal fashion, he gave the middle finger to the downed fighter and the crowd while running excitedly.

"[104]Despite the crowd actually cheering him back,[35] pundits found the act as extremely offensive and unsportsmanlike,[105] among them Dream executive Keiichi Sasahara and Aoki's trainer Yuki Nakai.

[108] Therefore, virtually all of his stand-up game is focused on taking his opponent to the ground, utilizing chain combinations of wrestling and judo techniques from the clinch to secure his goal, as well as the more dramatic guard pulling.