15000 miles. Take note that the awards originating from Japan do not allow you to make stopovers in Japan; you can only connect. (But you may have up to 24 hours to enjoy Tokyo, or Osaka, depending on your connecting point, if you plan carefully.)

If your trip takes place between December and February, you can take advantage of discount mile campaign, and you will only need 12000 miles. It has more restrictions than regular awards, and it has to be booked on-line, but if you can live with it, this is a great deal.

I don't have time to look for English info, but here is some info in Japanese.

kojiro