I created this to use up shiso leaves. I didn't have any umeboshi paste, but I think it would add a nice touch.

Processed cheese is easier to cut at room temperature.
This is an unheated item, so it's a perfect filler for cold bentos.
I don't use plastic picks for my family members who microwave their bento, but I use cute picks when I serve these as hors d'oeuvres. Recipe by Karupinetto