 Yes onigiri can be frozen very successfully. Just wrap them individually in plastic wrap (cling film), and then in a freezer box or bag to protect it from freezer burn. You can defrost the onigiri in the refrigerator gradually, at room temperature, or zap it in the microwave. See Keeping onigiri fresh and more Don't keep frozen onigiri in the freezer for too long, or they will eventually get freezer burn.  Yes onigiri can be frozen very successfully. Just wrap them individually in plastic wrap (cling film), and then in a freezer box or bag to protect it from freezer burn. You can defrost the onigiri in the refrigerator gradually, at room temperature, or zap it in the microwave. See Keeping onigiri fresh and more Don't keep frozen onigiri in the freezer for too long, or they will eventually get freezer burn. 