[1] Kawaguchi made his mixed martial arts debut on April 13, 2007, at DEEP: 29th Impact and defeated his opponent Hirotaka Fujiyama by majority decision.
On October 23, 2008, Kawaguchi defended his title against Mongolian challenger Baru Harn aka Seryu at DEEP: 38th Impact.
With both men gassed by the second period, the fight quickly devolved into moments of sloppy punching and leaning on each other in the clinch.
Mizuguchi recovered, however, tossed the champ over his hip in the harai-goshi and landed in side control, where he squeezed Kawaguchi's head with a neck crank.
Though his face was red and swollen, Mizuguchi would not go down, prompting Kawaguchi to switch tactics midway through the bout, as he chopped him down with kicks.
On May 7, 2010, Kawaguchi faced 5-time World's Strongest Man Mariusz Pudzianowski at KSW XIII: Kumite in Katowice, Poland.
Kawaguchi got some strikes in on the Pole in the second round, but Pudzian scored two takedowns, likely the convincing factor for the judges, who ruled in favor of Pudzianowski, who won by unanimous decision.