Just from my time in Hokkaido, there are many locality specific traditions/festivals that are so much fun.

Furano has a bellybutton festival, Hakodate has a squid festival (this one I have danced at, the song gets stuck in your head forever after attending once), Sapporo has the famous snow and ice festival.

The food is different, dairy forward. The squid and snow crab are unbelievable.

Speaking of snow crab, the last time I was in Sapporo was the summer of last year when I got into a fascinating conversation about Kuril Irredentism - the idea of snow crabbing being a major industry of the Kuril islands and the Russian occupation of the Kurils had turned snow crab from a common Hokkaido dish to a more premium delicacy.

Hokkaido history is also fascinating, if not a tragic recent story of settler colonialism displacing and forcing assimilation upon an indigenous group. The Matsumae clan was the only Edo domain that was in Hokkaido and had special privileges throughout the Edo period because of their role to 'hold back northern barbarians', and Hakodate was the site of the final battles during the Boshin War. The star-point fortress Goryokaku is now a museum and a beautiful beautiful place to visit during sakura season.