This is not directly related to Go, but many Go players want to visit Tokyo, and food is a good part of the experience.
Isari Juuhachiban (漁十八番, literally “Catch No. 18”) is an izakaya specializing in fish. It is in a side street near the “Shibuya 109” department store; see Google Maps.
The restaurant gets busy in the evening, especially on weekends, so it’s a good idea to reserve a table.
I can recommend the “sashimi moriawase” (sashimi selection), but everything you can see in the photos was very nice.
There is otoshi (a small appetizer for a ¥500 seating charge).