About 1,000 years ago, some Japanese soldiers were attacked while boiling soybeans for their horses. They quickly stuffed the beans into straw bags and when they finally got around to unpacking them a few days later, they had fermented. The soldiers ate them anyway. Thus, the beginnings of natto.
Today, natto is made by fermenting soybeans with Bacillus subtilis. The fermentation process creates a slimy, stringy texture and rather pungent, stinky cheese like odour. This stuff is awesome. I was warned by my couchsurfing host in Kyoto to avoid getting any on fabrics as it is difficult to remove. I believe you and heed your warning.
I don’t know if it is easy to acquire outside of Japan, but if you find some, it is worth a try.
The similar Korean version is called cheonggukjang. It is even stinkier.