A humble-chic shokudō (everyday restaurant) run by some clever gourmets. The emphasis on fresh local ingredients means that the menu changes frequently; pictures and English-speaking staff can help you with ordering. Pretty much everyone orders teishoku (set meals) featuring fish like saba (mackerel) cooked in mirin (sweet rice wine) or the typically Fukuoka goma-saba (sashimi-style tossed with sesame).
There are chicken and beef dishes for the landlubbers, and the place even makes its own furikake (sprinkles for your rice) using local ume (pickled Japanese apricot).
There's no English sign, but look for the decorative saba (mackerel) hanging outside the door, just east of Watanabe-dōri.