Onigiri is a Japanese food made from white rice formed into triangular or cylindrical shapes and often wrapped in nori (seaweed). Traditionally, an onigiri is filled with pickled ume (umeboshi), salted salmon, katsuobushi, kombu, tarako, mentaiko, takanazuke (pickled takana, Japanese giant red mustard greens) or any other salty or sour ingredient as a natural preservative.