although it is not customary to cook natto, natto may be prepared in food items like sushi or "donburi". "donburi" is any japanese dish served with rice in a bowl. natto can be made into a donburi by adding natto and other items like tuna or egg to rice inside a bowl. "nattojiru" is what people add natto to miso soup as a seasoning. also natto is used for topping when we eat soba, udon, spaghetti, okonomiyaki and so on.