After RINGS's demise, Kosaka wandered between Pancrase and the MMA division of New Japan Pro Wrestling. He then landed in PRIDE Fighting Championships, in which his first fight would be a rematch against Fedor Emelianenko for the latter's technical defeat in RINGS, taking place in PRIDE Bushido 6. The fight was one-sided and brutal, with Fedor landing strikes through Kosaka's guard while the Japanese tried unsuccessfully to counterattack with leglocks from the bottom. At the end, after taking punches during most of the round, a bloody Kosaka's corner threw the towel between rounds.