Stephen Bohrer, an M&A lawyer at Nishimura & Asahi, recently gave this presentation at a seminar in Palo Alto on the top five issues to consider when conducting M&A due diligence in Japan (in comparison to US transactions).
The Board Director Training Institute (BDTI) is a "public interest" nonprofit in Japan dedicated to training about directorship, corporate governance, and related management techniques. It is certified by the Japanese government to conduct these activities as a regulated nonprofit. Read a summary about BDTI here, and see a menu of its services for both corporations and investors here.