Here's one tour we did in Northern Japan:

http://www.celebrazio.net/bicycling/...week/2009.html

It was 6 days of riding, mainly, at just under 100km a day.
A video up there too. We travel pretty light, which is possible in Japan. We're all working so we don't take too many days off.
Another great tour is the Japan coast-to-coast, which I've done 5 times on 2 different routes. It can be as short as about 200km or zig zag along to about 500km. I do one coast-to-coast ride which is 400km in 3 days.

Get in touch if anybody wants to join one.