instruction: What is an onigiri made of?
context: Onigiri (お握り or 御握り), also known as omusubi (お結び), nigirimeshi (握り飯), or rice ball, is a Japanese food made from white rice formed into triangular or cylindrical shapes and often wrapped in nori. 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. Most Japanese convenience stores stock their onigiri with various fillings and flavors. There are even specialized shops which only sell onigiri to take out. Due to the popularity of this trend in Japan, onigiri has become a popular staple in Japanese restaurants worldwide.
response: 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.