IZAKAYA
There are many "IZAKAYA" restaurants in Marunouchi area. You can hop into one of the building and there are many types of cuisine and pictures which would tell you what they are.
Here are some recommendations from local.
TSURUTONTAN is a famous UDON noodle Izakaya restaurant which has also opened one restaurant in New York.
You should try "TEMPURA OUDON" and you can get up to three portions of udon for the same price.
Japan, 2-7-3 Marunouchi,Chiyoda-ku,Tokyo Tokyo Bldg. B1F
Photo source: Marunouchi.com 4.6.2016