Niku: meat.
Maki: roll.
Onigiri: rice ball.
Get it?
Nikumaki onigiri are rice balls rolled in meat, kind of like wrapping them in nori seaweed, as you can read about here: http://geigerdigital.com/andy/?s=onigiri. Nikumaki Honpo, on a corner of the shopping and nightlife district in the southern city of Miyazaki, created these about a decade ago. They’re great for a night out on the town when you need bulk stat. They are served with a lettuce leaf, which I suppose redeems it a tiny bit.
Maybe?