While it originated from Japan's 'onigiri,' in Korea it's called 'samgak gimbap' and has become a staple convenience store food. It implies something that's especially popular with students and office workers because it's affordable and filling.

This emoji doesn't just mean rice; it can also symbolize the 'anticipation' of discovering the various fillings hidden inside, like tuna mayo or bulgogi. Thus, it's used as a fun metaphor for "plain on the outside, but special on the inside!" or when asking a friend which flavor they prefer.