[Firebird]

I lived in Japan for 1 year and tried to do some couch surfing there. Just let me tell you that it is quite unlikely that a japanese person will invite you to their home. There are a few on the couchsurfing homepage, give it a try.

I also have to add that most people in this forum are actually not japanese but expats living in Japan. They are the most likely to host you in Japan, also if you go through couchsurfing.
I got invited by japanese people to stay at their place twice, once while hitchiking and once while travelling a road less travelled by foreigners.

That beeing said, i hope you find somebody, good luck and have fun!