Hanauta (direct translation: nose-song, aka humming) is a quick walk from Yotsuya-3-chome station, and off the main road so practically no-one could discover it serendipitously. It is worth looking for, especially if you like chicken noodle soup, delicious fresh gyoza, or if you just want to eat ramen in a relaxed atmosphere.
This is the coziest ramen joint I've seen. Most ramen places are crammed shoulder to shoulder and no-nonsense eat-and-go, in contrast Hanauta has a relaxed cafe-like atmosphere, lots of seating and even room for multiple families with children and strollers/buggies/prams.
Price performance is amazing, especially at lunch. For less than ¥1000 you get a large bowl of noodle soup, 3 perfectly crispy gyoza, and a rice bowl topped with meat and veggies.
The ultimate dish here is their "white soup" chicken ramen which is limited to 20 servings a day, it's full of collagen and extremely popular among the ladies. I love it because it is mild, rich, and delicious.