Hopefully, you already know about Natto 納豆 (Fermented soybeans). It is a popular Japanese food and known as a healthy food, but some people don't like the strong smell and sticky taste.
Photos
This is a real traditional Natto. 1 pack costs about 200 yen.
Natto was made with straw long time ago. Unfortunately it is difficult to find it these days. Manufactures usually use polystyrene foam or something instead of straw.
Why not try straw Natto in Japan?
Open the straw package. Usually small packs of sauce and mustard are included.
Put the Natto into a cup, and then mix with the sauce and mustard.
You are ready to eat. Put it on rice.
Information
Where to find straw Natto in Tokyo?
Store name
IBARAKI sense (Old name: Ibaraki Marche 茨城マルシェ)
Store (Restaurant) name
SENDAIYA せんだい屋
Some beef bowl chains below offer Natto, but there is no straw Natto, but it is worth trying.
Look over their menu about Natto on the official websites.