Mr. Shorty,
As Baka Dasai mentioned, there are many places to ride in Japan because of the mountainous terrain. Would also recommend to check out snowjapan.com as it includes a lot of good resource information on resorts and there is forum with several foreign members. Many of them are teachers.
My winter experience over the last few seasons has been great.
I am based out of the Nagoya area and have spent the last 3 seasons riding mosty in Gifu Prefecture, Nagano Prefecture with an occassional jaunt to Niigata Prefecture. My work commitments are pretty hectic but still managed 25 days on the snow last season. Even snuck in 1 race and about 5 days of gate training. Have had some unbelievable powder days here as well - one thing I never expected.
The alpine scene here is a little stronger than in the US. Joined a shop club last season and made some good Japanese alpine friends. There is an organization called the JSBA that runs quite few races and instructor clinics all over Japan. Like the US, Freestyle and Freeriding are very popular. You will have no trouble meeting people who are into Freeriding.
How is your Japanese? Mine is pretty weak so living in a bigger city has made life a little easier. If you will have a car with a navigation system and snowtires you can get to the resorts fairly easy. If your Japanese is good, you can get around on trains and buses without too much trouble.
One recommendation is to bring most of the equipment you plan to ride with you. Boards, bindings and boots are really pricey here. Many current model alpine decks are in the $900 to $1000 range. There are some decent board companies here (Moss, Gray, Ogasaka and BC Stream) but again the prices are way steep.
Hope this helps!