how to get onigiri like this?

hi! this is my favorite onigiri but it's like $5 and I'd rather just make it if I can. it doesn't list what it is but it's a very savory taste.
I've tried mixing in bonito furikake both dry and while the rice cooks but it was no where near as nice… maybe it's cooked in dashi stock? does anyone have any ideas?
I'm fine with experimenting as it just means I get to eat extra onigiri lol

by aSimpleFerret