I'm not sure if Mixi and Ameba is the right place. Lots of youngster or housewifes there with only the passion to do some virtual gardening or chit chat about fashion and celebrities. Facebook might be a possibility, it has a growin' community in Japan. There are some Basketball teams with websites in Japan. Could be a nice option to place an advertisment banner there. There is one team established in 2010 here in Miyazaki which I support
(http://www.shining-suns.com)The crazy thing is that we only would need, let's say, 50 people out of 120 million in Japan to play this game on a more interesting basis. Unfortunately I can't bring some of my family onto this (my wife is japanese and some of my relatives are all over Japan:) because they are going the japanese way of endless studying and working with no free-time at all.
Well, I guess BB is concentrating on the leagues in countries with hunderts of user. To keep smaller countries like Japan is not much work to do for them in the database. At least I hope we won't disapear as a nation and become a league with other ones.
The method of learning Japanese recommended by experts is to be born as a Japanese baby and raised by a Japanese family, in Japan. And even then it is not easy...