We waited a good hour to get in, but a better option is their katsudonsando at lunch time, which is available from their permanent food truck a couple of blocks away on 2 Chome-16 Shimanouchi.
Katsudonrestaurant opened by an ex-sumo wrestler with a monster 5cm cutlet option. It was good, but be prepared to wait. Lunch option may be better as a sando.