The bike was in perfect condition (Honda NC750X). I made about 1,600km: from Tokyo to Fuji, few lakes and passes around the mount, then to Kofu, Takayama and Kanazawa through the small winding roads and passes. From there I rode to Kyoto and then back to Tokyo, sidetracking to the Izu peninsula and it's mountain and coastal roads.
It is incredibly easy to ride in Japan, the roads are excellent, the drivers are unbelievably polite and careful and everyone drives responsibly. Did not see any car accident too.
Few advices: My trip happened in November 12 - 22. It is getting a bit cold in the mountains especially after 3 - 4 pm. Need to dress appropriately or ride in the warmer part of the year. The foliage time was mostly over in the mountains too. I have not booked any hotels in advance - just rented it from my phone over the Internet at the end of each day where it happened to be. Had always been able to find something in vicinity of 10 miles for $30 - $80 /night except Tokyo and Kyoto. Well, it is possible that in season the situation with the hotels can be different.
The country is beautiful and the food is great, plus a lot of interesting places everywhere. Between the few English road signs and the google maps on the smart phone (plus Bluetooth head phones) I had no problems finding my ways. I do not speak or read any Japanese at all.