Tokyo in spring for the cherry blossom festival. Kyoto all the way.
Hi Norman 🙂 Summer is the most festive time of year in Japan, with colorful festivals throughout the country, you will be able to hike in the Japan Alps, and enjoy the sea on the coast as well. You will have to book everything in advance as it's holiday season in Japan so many locals will be on vacation too!
For me the best moment to go to Japan is definitely April, you will be able to all cherry blossoms in bloom. But it's also the moment where you will have many many tourists. I don't advise you to go there at the end of April and beginning of May because it marks “golden week” in Japan, many people are on holidays at that time so to transports will be crowed especially in destination where Japanese people like to go on Holidays.
Beside Tokyo, I recommend you Hakone, it's probably the best place to see the Mont Fudji, even if you have to pick a clear day to don't have the half of the Mont hidden by clouds.
Enjoy your trip x