Brown rice Oats Millet Forbidden rice (Black rice)
The most popular seasoning for Nattō might be soy sauce and I like to eat that way of course but why not add some more variety on it? My No.1 nomination seasoning for Nattō would be Rāyu dressing sauce. Also, I would recommend to put few more topping in your bowl like grated daikon radish (without juice), boiled daikon radish leaves and shredded Nori. Mix everything when you eat like this.