I've never really looked that seriously at Shirokane Takanawa as a dining area but, after having recently stayed there for a month, I can report that there are actually quite a few interesting little places around the 'hood.
Magure is a small okonomiyaki joint opposite the Esso at the end of Kitazato Dori. Be careful not to miss it as it is so discrete that it really looks like it's part of the Salvatore Cuomo restaurant which it is next to.
I'd recommend this place for atmosphere and experience. Their okonomiyaki is unique in that the pork gets sort of "tempura-d" before they add it, and also that they have a unique (well to ignorant me anyway) range of seasonings. I went at lunch but the atmosphere seems like it would be really good in the evening.
I found the okonimyaki a bit undercooked to be honest so I am not giving top ratings to the food, but go along anyway. I'm sure you'll have a good experience.