Nairobi is pretty far from the sea, and I normally would hesitate to eat raw fish in such a location, but Misono, which has opened in a brand new office/shopping center in Kilimani, serves good and authentic Japanese food, including respectable sashimi and sushi. They have bento box lunch specials, which are a treat, as well as a full range of other dishes (gyoza, udon, katsudon, etc.) as well as teppanyaki. I haven't tried everything they have, but my lunch was very good, the tempura perfect and both cooked and raw fish excellent. A Japanese woman in our group pronounced the rice "too sticky," (I didn't notice) but said the food was "pretty good" and that she would go back. Lunch cost about Ksh. 1,400 per person, drinking only tea and water.
If you own or manage Misono, register now for free tools to enhance your listing, attract new reviews, and respond to reviewers.