is a retired Japanese mixed martial artist, submission grappler and professional wrestler who competed in the Heavyweight division. A professional MMA competitor from 1994 till 2022, he has competed for the UFC, PRIDE Fighting Championships, RIZIN, RINGS, Pancrase, and DEEP. Kosaka is the former King of Pancrase Super Heavyweight Champion. Kosaka is considered to be one of the early pioneers of mixed martial arts and was one of the top ranked Japanese fighters for several years. Known for his grappling skills, Kosaka is trained in judo and shoot wrestling, His "TK guard" position, a precursor to modern butterfly guard, is famous for its efficiency; former UFC champions Frank Shamrock and Maurice Smith have both credited him with having vastly improved their grappling from that particular position. Background Training in judo since highschool, Kosaka competed extensively during his stay at the Senshu University, where he befriended future world judo champion Hidehiko Yoshida. After graduating, Kosaka became a professional judoka under the sponsorship of Toray Industries, but was forced to retire after a knee injury. After a year, he joined shoot-style promotion Fighting Network RINGS where he began training in catch wrestling under mentor Akira Maeda. Mixed martial arts career Fighting Network RINGS Kosaka had his first mixed martial arts venture when, thanks to his strong judo background, he was sent to represent RINGS in the gi-clad MMA event Lumax Cup 1995. He won the tournament by knocking out Hiroyuki Yoshioka, submitting Susumu Yamasaki with a heel hook, and finally outclassing Brazilian jiu-jitsu champion Egan Inoue at the finals with a mix of judo throws and positional reversals. After his return to RINGS, Kosaka was put in opening shoot matches, defeating names like Maurice Smith and Willie Peeters. In September 26, 1997, however, he was thrown to a greater challenge when he faced former Pancrase star Frank Shamrock. Tsuyoshi controlled the match, throwing and taking down the lighter Shamrock and threatening him with submissions, but couldn't lock any of them, while Shamrock was successful at defending from half guard and counterattacking with his own hold attempts. After a failed takedown, the judoka was caught in a guillotine choke by Frank and had to spend a rope escape. Even although Kohsaka later clamped a Kimura lock which appeared to carry potential to finish the match, the time ended without Kosaka completing the hold, thus giving the win to Shamrock for his scored point.