
This is one of many restaurants for "single" customers that I have encountered in Japan and nowhere else in the world. They don't check your marital status at the door, it just isn't designed for party of more than one client, no tables for 2 or more etc...
You come in, make your selection in a self service machine that prints out a ticket that you hand over to the chef at the counter who cooks it fresh in front of you, and you leave, without the need to utter a single word to anybody in the restaurant