14-15 nights trip:
Osaka** - Kanazawa - Shirakawago - Nagano - Tokyo
** Land at Osaka and spend 1 night in Osaka for eating and shopping galore. Luggage forwarding service for the big luggages to Kanazawa. To bring small bag for overnight clothing/etc.
Not sure if there’s direct transport from shirakawago to nagano but in this region, I liked takayama and it’s a convenient bus route from Kanazawa - shirakawago - takayama. From takayama can go to shin-hotaka ropeway and hirayu onsen
Which season are you going? There’s also the alpine route if you are not going during winter
My route is narita - nagano - Kanazawa - shirakawago - takayama - Matsumoto - narita
I took the flexible 5 days rail pass. In hindsight, with this rail pass I should have replace Matsumoto with Toyama to save some bus fare. But having said that, Matsumoto castle is gorgeous and should not be missed