Nattokinase comes from fermented soybean and is a common food in Japan. If you’ve ever seen Natto, you’ll know that it doesn’t look particularly appealing (I tend to think of a bad cold every time I see it). I have never tried it myself so cannot comment on the taste. However, I found this entertaining video of a guy trying Natto for the first time.
After he finishes, I thought he was going to bring it up again
If you do eat Natto, and want some serving suggestions, this lady shows you different ways to eat Natto.