Spam and egg onigiri costs 300 yen ($1.90); the one adorned with several types of “konbu,” or edible kelp, called “Dashi Punch X3,” costs 280 yen ($1.80). “Onigiri is the infinite universe.

There are no fixed rules. Some people sprinkle their onigiri with sesame seeds. Oboro kombu, or shaved kelp, is another favorite. Or enjoy it plain. Easy Onigiri, from AP's Yuri Kageyama Start to ...