Kobe native Koji Oishi took up wrestling in high school specifically because he saw it as a good fundamental base and path to a career in MMA. After successfully competing as a wrestler – he was ranked top 10 in the nation in both high school and university. He made the transition to professional MMA in 2000. In the decade since then, Oishi has competed throughout the world, defeating some of the sport’s most well-known fighters, and ultimately being crowned King of Pancrase.

One May 31, 2013 Oishi fought Honorio Banario for the vacant ONE FC Featherweight Championship. Oishi KO'ed Banario early in the second round to capture the title.

Oishi would then have a rematch with Banario at ONE FC 13 - Moment of Truth on December 6, 2013. The two would fight until the third round, when Oishi would again win via KO. 

Oishi's next fight would be at ONE FC 19 - Reign of Champions on August 29, 2014. He would face Jadamba Narantungalag in a bout that went the distance, with Oishi coming out on the losing end of an unanimous decision.