noun
hinomaru bento
A simple bento consisting of plain white rice with a single red pickled plum (umeboshi) in the center, resembling the Japanese flag.
子供の頃、遠足にはよく日の丸弁当を持って行った。
When I was a child, I often brought a hinomaru bento on school excursions.
Umeboshi is the pickled plum itself, while 日の丸弁当 refers to the entire bento featuring an umeboshi on rice.
From 日の丸 (hinomaru, the Japanese flag) + 弁当 (bentō, boxed lunch), named for the visual resemblance of a red umeboshi on white rice to the flag.