For the same reason, any decent Combini (convenience store) in Japan will have at least one dedicated rack with a variety of onigiri. Here are some of the most common types and the personalities that favor them:
1. 鮭 Shake/Sake
Salmon that is grilled with salt then shredded, it should always be perfectly seasoned and not dry. People who favor this filling tend to take things slowly. They are also deliberate, strong-willed and steadfast in their principles.
2. ツナマヨ Tuna Mayo
Sometimes also called シーチキン (Sea chicken), the tuna should not be overwhelmed by the mayonnaise, and the mix should be creamy and slightly tart. People who like this filling are said to be of pure heart and possess inner beauty, but also have a tendency to be hard-headed.
3. 昆布 Kombu
Shredded Kombu (edible kelp) that is cooked in a soy sauce based mixture until tender, it should taste slightly salty and sweet. People who like this filling are said to favor simplicity. They avoid complications and prefer things (and relationships) that are straightforward.
4. 明太子 Mentaiko
Mentaiko or spicy cod roe, is sometimes mixed with karashi (mustard), mayonnaise, egg or other ingredients. People who choose mentaiko are tuned in to new trends and are up to date. They also tend to be good at fashion, cooking, and/or socializing.
5. 梅干し Umeboshi
Salty and sour pickled plum, it is sometimes cut up and mixed in with the rice. People who prefer umeboshi in their onigiri are said to be faithful and reliable. They also tend to be extremely detailed and prefer to do things properly.
Other types of onigiri
焼きおにぎり Yaki onigiri - Rice basted with sauce and grilled without filling.
おかか Okaka - Dried bonito flakes seasoned with soy sauce.
赤飯 Sekihan - sticky rice steamed with adzuki beans, tinting the rice with a reddish color.
Also check out our other Combini Checkout articles:
Combini Checkout: A beginner's guide to bottled tea
WAttention Ninja Writer Profile
I’m an amateur writer and avid reader who's been living in Japan since 2007. I enjoy reading and writing about food, travel, and quirky trivia. I treat 100 yen shopping as therapy.