Japan 4 days/3 nights

I’ve traveled to Japan over 20 times all for work - Tokyo, Osaka, Toyama, Yonezawa, Okayama, Ube, Mito, Fukuoka. I absolutely love Japan and I swore the next time I go will be purely for me. Would love suggestions of where to spend 4 days/3 nights coming of a China work trip. This limits me to essentially one geographical area and will be flying from Shanghai Pudong which puts me to Tokyo, Osaka, Fukuoka, Nagoya for sure. Looking May-June 2025. Thanks!