One of Japan's many soy products to be experienced, nattō is fermented soybeans. I think there's much to be said about it. It generally isn't restaurant food. It's quite economical, about a hundred yen for a three-pack (sometimes four). It's gooey. It's unpleasant to wash dishes that are coated in nattō remnants--at least for me it is. It's an excellent source of lean protein. It feels gross to some people to have nattō's texture in their mouth. Above all, above all else, first and foremost and most predominantly, at least in terms of first impressions, is its horrid and wretched smell. Well, maybe I'm exaggerating about the smell.
Actually, I like nattō. I eat it. I don't like the smell, but I enjoy its taste and don't really mind its texture (in my mouth, at least. Getting it on my hands is something else). But the part about not wanting to wash nattō-coated dishes will probably not change in this lifetime. The first time I ate it was in curry, which was quite a mistake. The second time was simply over hot rice, which was quite good. It's called nattō gohan. You put yellow mustard on it and pour the sauce on. Much less commonly, the yellow mustard can be replaced with wasabi, Japan's horseradish. (I've only seen this once, in a supermarket.) A lot of people will mix a raw egg with the nattō. (I find that just about all of my friends who grew up in Japan have an unshakable trust in the eggs produced here and will eat them raw anytime, any place, without fear of salmonella.) You can also put on top of it okra, shirasu (tiny, tiny fish), or strips of nori (dry roasted seaweed). You can eat it as sushi (the nori maki, or makizushi version); 7-11 usually sells it. I know some who eat it on toast, and one of my students eats it plain and cold, just out of the fridge.
The Wikipedia article on nattō goes on to detail some of its health benefits, as promoted by the industry and other proponents of nattō. It contains a compound known as pyrazine, which is supposed to deter blood clots. It’s said to be rich in Vitamin K and calcium, both helpful in maintaining bone strength and preventing osteoperosis. I like that the article states that nattō "may be an acquired taste." In fact, I do know a fair number of Westerners (and foreigners from the East, as well) who eat it willingly. My friends who can't stand it watch me consume with disbelief. One of them, one of my best friends here, always felt that Japanese people who like nattō do so with a measure of pride, as they expect most foreigners to find it unendurable. I remember this one time he had a little taste. As he slowly chewed, savored, contemplated, he said, "No. No. Usually, even if I don't like a food, I can kind of imagine what someone else would like about it. But no, not with this." It was a wall that he would not be climbing, though he wished otherwise. "I want to like it. I wish I liked it. I just. . .can't!" As I tried to assure him that things would be okay, that it was no big deal, he eyed me with caution. He said that he suspected I carried a bit of pride myself in being a foreigner able to eat fermented beans. So far as I can tell, to the extent that I am aware of myself, I don't. In the company of foreigners, I actually feel a tad embarrassed to be eating these stinky beans, but—oh well! I gotta think it’s okay to like healthy, inexpensive, bad-smelling food.
Some pictures of an eatery that serves nattō, and the dish called nattō gohan: