You might want to flip Osaka, Kyoto, Nara around new year with another portion so more restaurants are open unless you want to visit shrines while a lot of people are there for the New Year https://www.japan-guide.com/e/e2276.html. There's also the Yamazaki distillery tour which closes around New Year (reserve as early as possible) https://webapl.suntory.co.jp/factory/yamazaki/?lang=en

I think winter is crab season near Kinosaki onsen and Tottori beef is the ancestor of the branded Kobe wagyu. It might also be oyster shack season in Hakodate and Fukuoka. There's also a squid food truck in Hakodate - I think it was introduced on this episode of Journeys in Japan https://www3.nhk.or.jp/nhkworld/en/t...s20150204.html but you should also be able to get it at restaurants https://savorjapan.com/contents/disc...squid-capital/

Do you like modern art? It is a Setouchi Art Fest Triennial year. If you're considering the side of Shikoku bordering the Seto Inland Sea, the Setouchi islands should have some the permanently displayed works still available. The ferry might be infrequent on a winter schedule https://setouchi-artfest.jp/en/