He retired as a kickboxer in late 2011 after going undefeated as a pro (12-0-1) and capturing the NJKF belt. I've heard he was trying to become a lawyer.
No clear reason given for his retirement, but its likely that with FEG collapsing around that time, he didn't really see a sustainable career in kickboxing. Which is a shame as guys of that generation that stuck with it (e.g. Noiri, Koya Urabe, Takeru & Kimura to a lesser extent) went on to become big stars.
Then again, who knows what happens down the line. Kenji Kubo went on to return to K-1 and start up his own K-1 gym with K-1 Japan gaining steam. The Ishida brothers are starting to become active in kickboxing again and trying to make it to K-1 Japan. If only we get back Kusakabe and the all important Akimoto... and if someone finds wherever Shota Shimada is hiding.