Many readers have raised objections about the halalness of the tuna-fish based onigiri from 7Eleven. However, according to whatever information we could gather regarding the onigiri mentioned on this page, it is Insha Allah, considered halal. The name of the rice and fish-based ready-to-eat food item is Tuna Mayonnaise Onigiri. You can find it at any 7Eleven convenience store anywhere in Japan.
It is used as a ready-to-eat meal if you do not want to spend a ton of money and do not have much time to find a halal restaurant nearby. You just grab it from the convenience store and start eating it. No waiting needed at all.
Now, let us get into the details of what ingredients this onigiri has. It has ethanol, a type of industrial alcohol that is permissible to consume if it is less than .5% in the finished product in question.