Fish has always been among my favourites, so living in Japan feels like landing in paradise, you have so much choice, always of quality.
Here is a restaurant on my top list, in Nogizaka, walking distance from Roppongi, 2 blocsk from Midtown shopping, called Uoshin Nogizaka. From outside, it looks like nothing, inside as well, haha, but the food is great and there is a nice atmosphere, I am a regular there. In season, they serve fugu. But on a normal visit, I will always go for sashimi, hairy crab and grilled octopus, delicious!