Some info about JAPANESE
Onigiri 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.
Wikipedia contributors, "Omusubi," Wikipedia, The Free Encyclopedia,ABOUT THE JAPANESE LANGUAGE