After a childhood marked by a spinal condition which required surgery three times, Masakazu had his first contact with combat sports at age 18, training kickboxing and Catch wrestling at the Fujiwara Dojo by Satoru Sayama's mediation. He later moved to Antonio Inoki's Universal Fighting-Arts Organization, and then Kingdom Ehrgeiz, where he trained Shoot fighting and MMA with Hidetada Irie before doing his amateur debut.
ZST
Imanari gained popularity during his mixed martial arts career in Japanese promotion ZST fighting the likes of top Lightweights including Dokonjonosuke Mishima, Jorge Gurgel and Marcus Aurélio despite being a much smaller Featherweight. He defeated Gurgel, who is a Brazilian jiu-jitsu black belt former UFC fighter via Catch wrestling staple submission while being a lighter in weight. Imanari also defeated former Cage Warriors Featherweight ChampionDanny Batten. In the first round Batten took Imanari down on the ropes but Imanari attempted a triangle choke. Batten escaped it but Imanari then transitioned to an armbar causing Batten to submit in just over 40 seconds.
DEEP
Imanari moved on to compete in DEEP where he defeated a top WEC contender and the former WEC Featherweight ChampionMike Brown via submission where Brown's leg became dislocated. Imanari now a top contender in DEEP went on to compete for the title shot against Yoshiro Maeda in which he defeated Maeda via submission to become the new DEEP Featherweight Champion. Imanari made his first KO victory in his first defense for the belt against Takeshi Yamazaki with an up kick.
Cage Rage
His next fight, which was his first fight outside Japan, was in London, England where he became the Cage Rage World Featherweight Champion by defeating Robbie Olivier with a flying armbar at Cage Rage 20. This accomplishment made him the only mixed martial artist in the Featherweight division to hold belts in two separate major promotions. He defended his Cage Rage belt for the first time against Jean Silva, winning by reverse heel hook in the first round, injuring Silva's knee in the process.
In 2011 Imanari returned to DREAM to take part in the DREAM Bantamweight Japan Tournament. He won his first two tournament fights in a single night defeating both Keisuke Fujiwara and Kenji Osawa at Dream: Fight for Japan!. The tournament finals took place at where Imanari faced off with Hideo Tokoro. Tokoro defeated Imanari to win the tournament, the second-place finish gained Imanari entrance into the Bantamweight Grand Prix. Imanari faced Abel Cullum in the opening round of the Bantamweight Grand Prix at Dream 17 at Saitama Super Arena in Saitama, Japan, on Sept. 24. He won the bout via submission in the third round. In the semifinal round at, Imanari lost to Antonio Banuelos via split decision.
On January 31, 2012 it was announced that Imanari would be fighting for ONE Fighting Championship, who have a partnership with DREAM which allows both organizations to share fighters. He faced unbeaten URCC Flyweight Champion Kevin Belingon at ONE Fighting Championship 3 at the Singapore Indoor Stadium on March 31. He won the fight via submission in the first round.
Team allegiances
Imanari left Catch wrestling based team Paraestra in 2008 and founded Nippon Top Team with Shinya Aoki and Satoru Kitaoka. However, Aoki left for Evolve MMA of Singapore, whereas Kitaoka joined Lotus Paraestra, Setagaya branch of Paraestra. Consequently, Imanari became a member of Team Roken. Imanari is an A-level Shoot wrestler under Yuki Nakai. He was later also presented a Brazilian jiu-jitsublack belt by Marco Barbosa of Barbosa jiu-jitsu.
Fighting style
Imanari is primarily a grappler, and is universally known for his skill and preference for leglocks, which gained him the nickname of "Ashikan Judan". Though his striking game is considered inferior, Imanari often engages in stand-up battles in order to bait the opponent to the ground, usually by dropping down after or while seizing control of his leg or by way of ashi garami. He stands out for his dexterity in toehold and heel hook variations, and is an avid user of the 50/50 guard in order to transition between submission attempts. He describes his signature leglock style as not based in sambo as it is popularly believed, but "purely self-taught", and explained his preference for it as "because it hurts the opponent". The "Imanari Roll" and the "Imanari Choke" are grappling moves named after him due to his usage of them.
