I have completed 100,000km touring Japan by motorcycle. I made this map initially just so I knew which roads I had explored because it got confusing with the extraordinary density of roads in this country.
It was never intended to be a guide for others but I decided to share it because information about riding in Japan for foreigners is limited and besides now I have seen more of this country then most people so this map actually has some good info.
If you open the map on to a new tab/page (use the brackets icon top right of map) then you can see the map legend and easy pan and zoom. Clicking on roads will usually give some description. Hotels are not positioned precisely and are just my own records of where I stayed previously.
As you can see there are good roads everywhere in Japan as you might expect in a land of mountains as well there are superb viewpoints everywhere.
If you are wondering where to ride first then anywhere away from big cities is enjoyable. Shikoku and the inland sea and Kyushu are my favourites but there are fabulous roads everywhere else. Hokkaido despite the marketing hype offers less twisty roads being flat farm land but Tohoku is spectacular so a ride north is as good as going south.
I have written much more detail about how and when to ride Japan in my Guide to Motorcycle touring Japan that tries to cover everything you need to know.