Boardmember.com has put many useful videos – short lectures or interview – on its web site. They span a broad range of categories. Not all are pertinent to boards in Japan, but many of them are, or the core concepts are. (You can select from the categories on the right.)
https://www.boardmember.com/brc_boardgovernanceseries.aspx
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.