Cooked conger-eel coated with a sweet soy-based sauce is a good finisher for any sushi dinner.
Conger-eel, or anago, is like unagi in that it has small thin bones that are meant to be eaten with the flesh. I would kindly advise against asking a restaurant to serve boneless anago or unagi as it would be a pain the you-know-what to filet one of those things. It is boiled or grilled and often coated in a heavy sweet sauce made from soy sauce, sugar, eel fats, and other ingredients bringing out its distinct flavor.
I’m unsure as to how the anago I received from relatives in Okayama, Japan was prepared, but unlike unagi, it was fairly mild in flavor — the relatives were kind enough to send it with little bottles of anago sauce packed separately.
Sweet and a bit tangy, it was a great way to end a 3 course sushi meal I made over the weekend which started with a garden salad, then aji and salmon nigiri, followed by a ham sandwich (you know, to clear your pallet…), and finally a few pieces of anago nigiri.
I took care not to put too much of the sauce on the anago after I had molded it with the sushi rice. Just enough to end the meal on a high note.
When ordering sushi in a restaurant, they say you should start with the least sweet fish and move your way up and finish with anago or tamagoyaki (sweet fried egg omelet). I don’t always follow this method. The thing is, ordering anago as your second, third, or even first piece can be a bit irritating to the sushi chef because he might think you’re not planning to stay long as something as sweet as anago is normally served towards the end.