Sushi Sakai in Fukuoka and Tenzushi in Kokura get mentioned for high end sushi.

On the fish market style, Karato Fish Market near Sakaiminato is similar to Aomori Gyosai and other Aomori/Hakodate market styles. It's a bit above Kitakyushu in Yamaguchi and the sushi setup is open on the weekends
https://www.karatoichiba.com
https://www.youtube.com/watch?v=zJUu53paA_g
Plenty of sushi shops surround it
https://www.youtube.com/watch?v=hy7PHi3_V6w

I think Fukuoka's known for kakigoya/oyster hut grilling in winter, mentaiko, and of course Hakata style ramen. It looks like the Canal City Ramen Stadium is currently closed https://www.fukuoka-now.com/en/news/...-indefinitely/. I'm sure ramen blogs would have some recs though Fukuoka is also home to some of the larger ramen chains if you're not a ramen hunter. It's also known for yatai/street stalls
https://www.fukuoka-now.com/en/itosh...ter-hut-guide/

Nagasaki- I prefer castella cake to other Nagasaki specialties like champon, sora udon, and kakuni manju. The others are more Japanese versions of Chinese foods and I eat enough of the Chinese ones as home/comfort food to probably be used to those tastes. I think Nagasaki castella is "worth the calories".