Guess what?! I just tried it at Sushi Zanmai but I am not sure how I feel about it :D

It kinda has the texture of a slimy okra (which is not too bad) and an after taste similar to the canned black bean fish. Think need to try a few more varieties haha.
That was fast. I forgot to mention the okra. It's interesting that it felt like those black beans to you. I love them too.
You have try it with different combination to find the right taste for you. I waste so much natto before I got it right. Many years ago, I toss out the rest after I had a bite. Then I forgot it. Few years later, a friend gave a natto snack, it was dried and crunchy like peanut. It has certain aroma about it. Very nice. But I couldn't it in the supermarket, only the frozen ones. I tried and threw them out again. Another few more year, I was watching Chibi Maruko eating natto. This time I added the shoyu and wasabi. Finally...I didn't want to mention this when you asked me about it. hehe