Destinations for 2nd trip?

Hi all,
I will be visiting Japan for around 10 days in May of next year. I spent over 3 weeks last December and absolutely loved my time there. During that trip, I hit all of the main tourist destinations: Tokyo, Hakone, Kyoto, Osaka, Nara, Miyajima, Hiroshima, Kanazawa, Shirakawa-go.

This time around, I have the option of flying into 4 airports: Tokyo, Osaka, Nagoya or Fukuoka. I was thinking of spending around 4 days in Kyoto and maybe a night in Koyasan, but I'd love to visit some towns/cities I haven't been before. I was also thinking of spending some time in Okinawa but wasn't sure if that would make sense logistically as I'd have to catch an internal flight, and I won't be in Japan for long.

I would love some suggestions for any places that you guys have loved, that are perhaps less touristy than the ones above. I'm looking for a mix of good food, shopping, nature and some history/culture.

You will spend 10 days in Japan, and allocate 5 days in Kyoto and Koyasan (Kansai area). If you want to travel to Okinawa, it's quite doable. The southern most airport Ishigaki is about 3 hours flight from KIX, NGO, NRT, HND and FUK. All of them have direct flight, but not so frequent. Which is most convenient depends on your international flight. After Ishigaki, you should fly to Kansai (KIX), and visit Kyoto and Koyasan. Of course you can do it on the opposite direction.

Ever considered Hokkaido? I know itfs not one of the places you listed but itfs worth looking into.

Fukuoka and/or northern Kyushu are less touristy. Makes sense since it's a arrival airport.

Add Okayama, Kyoto and Koyasan. You got a good holiday.

Shikoku is an other option.
There are plenty of options for about 5 days.

May is a lovely time to travel in Japan, wherever you go. If it were me, I would probably fly into Fukuoka and spend at least a few days traveling in Kyushu. There are so many places you could go. Some are fairly gtouristy,h but if you go on weekdays even those tend to not be very crowded, and May (after Golden Week) is off season anyway. Fukuoka itself is not my favorite city in Japan, but just because you fly into there it doesnft mean you have to center your trip there.

Himeji: https://www.japan-guide.com/e/e3500.html
Onomichi: https://www.japan-guide.com/e/e3475.html
Okunoshima (Rabbit Island): https://www.japan-guide.com/blog/far-flung/180912.html
Arima Onsen: https://www.japan-guide.com/e/e3558.html
etc., etc.