What differences in regional food culture in Japan have you noticed whenever you visit various parts of the country?

Don't even have the slightest idea where to start with this one. Too many possibilities. Miso, and ramen come to mind. The best of ANYTHING I have ever tasted was served on Kyushu, mainly the city of Kumamoto.

The taste of soy sauce amongst regions differs slightly. With Kyushu tasting a little sweet, Kansai tasting a little more salty, and Kanto tasting a little more full body. Nagoya uses their own Tamari type soy sauce which is considered the granddaddy of all soy sauce which is more full body than Kanto.

, Sapporo udon dish are served with a lump of butter. Pork dominate Kyushu ramen, The southern island are spam lovers and you find spam in a lot of dishes. between Osaka and Fujisan Green tea dominate a lot of dishies. Hamamatsu in the middle are big on eel. From Itonigawa along the coast to Niigate are big on Crab.

Zichi, I visit eateries all the time and had my best spot. At my best spots I always eat same dish and never alter. Like this ramen place opposite Ichinoseki station. I always have the double pork ramen. A place up the stair at Hakuba station bus stop I always have the yakisoba. When in Kitakami I will travel 30 km to Getokogen for their charcoal garlic ramen not for a ski, A Isakia in Ito I have the rice porridge. In Morioka I visit a eatery for the Okinomiyaki and I have visited Osaka. What I found out that the cook at Ichino is from Kyushu which is know for good pork ramen and the cook from Morioka is from Osaka where they know for good Okinomiyaki

Everything tastes of salt, sugar and soy sauce in varying degrees. And each region has its own totally unique ramen.