Natto

Natto is a food made by fermenting soybeans with natto bacteria (Bacillus subtilis).
After steaming the soybeans thoroughly and letting them cool, they are wrapped in a rice-straw bundle (warazuto) and fermented for around a day in the right environment; naturally occurring natto bacteria multiply and natto is produced.
This is the traditional method, but today natto is often made using cultured natto bacteria.

Natto is broadly divided into two types: stringy natto (itohiki natto) and salty fermented natto (shiokara natto, also known as temple natto).
When people simply say “natto,” they generally mean stringy natto.
Stringy natto is further categorized into three types: whole soybean natto (marudaizu natto), split soybean natto (hikiwari natto), and goto natto.

The most basic way to eat it is natto over rice (natto gohan): add the included sauce and mustard, mix well, then spoon it onto rice.
Japanese people also eat natto daily in many other ways, such as adding seasonings or ingredients, or enjoying creative dishes made with natto.