How many days in Japan?

Remove Takayama or Kanazawa rather than compressing every stop into too few nights.

Give the Alps an extra night or plan luggage forwarding between bases.

With less time, reduce Osaka or use it as a day trip from Kyoto rather than cutting all three cities into very short stays.

Add nights to Tokyo or Kyoto first, then consider Hakone, Hiroshima, Nara, or the Alps only when the core route has enough breathing room.

If time is tight, protect the Koyasan overnight or remove it entirely; turning the mountain stay into a rushed transfer day loses the main reason to include it.

Add time in Kyoto or Osaka, or insert Nara as a day trip, before expanding beyond Kansai into another long-distance rail corridor.

With eight or nine days, reduce Hakone to one night or use Osaka as a day trip from Kyoto rather than compressing all four bases.

With 12–14 days, add nights to Tokyo or Kyoto first, then consider Nara, Hiroshima, or another region only after the core route has breathing room.