Natto is awesome! You buy it in Asian shops in small, deep-frozen containers that look something like this:
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Inside, there are the fermented beans and two small, sealed plastic baggies supposedly containing soy sauce and mustard. As I do not read Japanese, and am not sure whether those seasonings are 100% vegan, I typically do not use them, but replace it with a bit of normal soy sauce. For creaminess, I typically also add a bit of mustard once the natto has de-frosted.
You eat it sparingly as condiment, e.g. a little bit of it, with some spring onions and some shredded nori leaves, on top of white rice, or in sushi.
IT IS VERY STICKY.
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Yes, it is an acquired taste, I have had friends saying it tastes awesome, but once a colleague said it was "the vilest thing he had ever eaten in his life" - that was not a very adventurous colleague, however.