I'm guessing Natto has a similar smell/taste to Korean Cheonggukjang (청국장), which smells like an a pair of wet moldy socks or old shoes, but the moment you get it in your mouth and the flavor your tastebuds detect combines with the smell your nose is gettings, it suddenly makes "sense" and is absolutely delicious -- an incredible hearty flavor with all these wonderful subtle under and overtones (sometimes with a hint of of a kind of smokiness). It's the weirdest taste hack I've ever encountered in food and one of my favorite Korean dishes.

It's made out of a kind of fermented soybean as well.

https://en.wikipedia.org/wiki/Cheonggukjang