Hi,
yeah the thing is the Kindle supports Japanese and it looks really great, but DTP is not supporting it. I thought that it would be may be possible to trick a little bit and make pictures and then upload to DTP. But like @DMSmillie mentioned it probably will not pass the check of DTP.
I think the easiest and most correct way is to wait until DTP supports Japanese and in the meanwhile I will publish my books on other platforms.