I work one a week in Oimachi, and always go for the pizza mazesoba over at Ajito Ism. Yes, I am obsessed with it a bit.
But Oimachi has some shops that have been around for ages in the alleys near the station. The entire area is a bit dingy and cramped, just the way I like it.
Kiccho's history is deep, and they make their noodles the old way; using bamboo sticks to knead the dough.
It's labor intensive, but this traditional method yields flatter, chewier noodles that draw massive lines every day. Not a lot of Tokyo shops do this, so Kiccho is a real gem.
Classic, classic, classic.
The menu is extensive, but you can go with the wontonmen if you want what I had.
Tokyo, Shinagawa-ku, Higashi Oimachi 5-6-6
Closest station: Oimachi
Open 11:30-14:30. 17:30-20:30
Closed Monday and Tuesday