With vending machine ( of course, this has all sorts of natto, from natto donuts to edamame natto ! ) set in front, Sendai-Ya, specialized in natto opened this past Saturday.
They have various kinds of natto including natto donuts.
We do eat natto here in Japan, still a shop " specialized in natto " is very rare.
Theirs are bit expensive.... still, they are about 200 yen average. ( I bought edamame natto which was... I thinks 180 yen for 3 packs and 230 yen for regular natto which has 4 packs.)
Unfortunately, there is no eating space.
Are you interested ? OK, take either Inokashira line or Odakyu line to Shimokitazawa.
Get off and come to the west exit. Take a right at exit and go up the stairs. Keep on going.
This shop will be on your right in 30 sec.