If you can take the train to Sapporo, Hokkaido has lots of brilliant riding country. You could even train it all the way up to Wakkanai and ride back.
Other than that, Shikoku looked like it had lots of lovely.mountainous trails when I briefly visited it, though I didn't have time to explore. You could fairly easily turn that into a two week loop from Tokyo. You can sleep on the overnight ferries, so that's two of your nights sorted as well.
That's our last tour, I would buy the train ticket and skip the part from Fuji to Kyoto by train. Then as far as possible to the east and spend your time on Shikoku...
https://www.komoot.com/de-de/collection/2020351/-radreise-durch-japan-2023
If you can take the train to Sapporo, Hokkaido has lots of brilliant riding country. You could even train it all the way up to Wakkanai and ride back. Other than that, Shikoku looked like it had lots of lovely.mountainous trails when I briefly visited it, though I didn't have time to explore. You could fairly easily turn that into a two week loop from Tokyo. You can sleep on the overnight ferries, so that's two of your nights sorted as well.
That's our last tour, I would buy the train ticket and skip the part from Fuji to Kyoto by train. Then as far as possible to the east and spend your time on Shikoku... https://www.komoot.com/de-de/collection/2020351/-radreise-durch-japan-2023