 Otsuka made the move from a successful professional wrestling career to mixed martial arts competition in 1995.He earned a notable victory over Vale Tudo pioneer Marco Ruas in 1998.Though Otsuka finished his career in 2006 with a 4-13 record, he mostly faced very high-ranked opponents, including all-time greats Renzo Gracie, Ken Shamrock, Igor Vovchanchyn, Quinton Jackson, Wanderlei Silva, and Anderson Silva, all of whom defeated him.