At first glance this place might be mistaken for a half hearted McSushi joint in the underground path, but it actually offers fantastic variety and quality of Japanese food. I find it funny that besides their internal seating, they also boast a "patio" (although you are still in the underground path when sitting there).
I have heard that going at lunch time is always too packed which leads to bad service. Also, I suspect that their quality of food is much worse during their rush time, but whenever I go in the evening the food is fantastic.
Best dish for me is the unagi pizza as well as their cuttlefish.
Ninki is surprisingly affordable, considering that it's location is in the heart of the financial district.