The only thing remotely Japanese that I've tasted, and disliked, has been Ikura. Oh, another food I've had and disliked, has been Edomame. My teacher gave me this. It was way too salty for me. I acted as if I liked it, especially when she gave me some another time, so I just accepted it to be polite.
Even though I've never had it, I have this feeling that I wouldn't like Natto at all, but of course, as I say, "Don't knock something until you've tried it."
As for stuff I've tasted and loved, I'd have to go with okonomiyaki, yakitori, and sukiyaki. I
I would say Ramen, but I've never had any decent ramen, imo, and by decent, I mean able to go to a stand and order some nice and fresh. The stuff in the cup doesn't cut it for me. With the Japanese restaurants around here, it's mostly Udon or Soba based dishes.