All-Japan Judo Championships
Ishii won a gold medal at the Junior World Championships on 16 October 2004 in Budapest, Hungary. On 2 December 2006 he won a silver medal at the −100 kg category of the 2006 Asian Games. On April 29, 2006 and 2008, he won the All-Japan Judo Championships in Tokyo, Japan. With him the Japanese team won the World Judo team competition on 17 November 2007 in Beijing, China, this time in the +100 kg division.