From 2000 to 2001, he was a Visiting Scholar at the Edwin O. Reischauer Center for East Asian Studies at the Johns Hopkins University School of Advanced International Studies (SAIS), Washington, D.C. After coming back to Japan, he taught as a Professional Lecturer at Keio University's Graduate School of Law from 2003 to 2007.
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From 2003 to 2004, he served as the Deputy Director-General of the Cultural and Organizations Department of the DPJ, as well as the Next Vice-Minister of Defense before becoming the Next Minister of Defense from 2005 to 2006.