(A bit old but useful) – This booklet is the sixth edition of Corporate Disclosure in Japan – Overview published by the International Relations Committee of the JICPA in order to provide both historical and current
information, including the above-mentioned content regarding the outline of the corporate disclosure system in Japan. I am certain that this booklet will help you to better understand an overview of the current status of corporate disclosure in Japan.
http://bdti.mastertree.jp/f/b7eptcx2
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.