Pressed By The Chef’s Loving Hand
So, to “nigiru” is indeed to grasp. Nigirizushi (sushi > zushi, at the end of a compound word; this makes it easier to say) is grasped by the chef and pressed together. It is formed of some sort of meat pressed on top of sushi. The above picture shows ebi, or lobster, in this case. The meat is pressed on top of the sushi while the sushi is in an oblong rectangular box (which simply means that fish/ lobster face forward when being pressed). The sushi (vinegared rice) thus packed provides a stable foundation, and the nigirizushi can then be served as-is.
A variant is known as the gunkan maki (“battleship roll”), using nori seaweed to form a perimeter around the sushi rice that constitutes a “vessel” that can be filled with soft toppings. This invention, pioneered by the Ginza Kyubey restaurant in 1931, greatly expanded the variety of toppings that could be used with nigirizushi.
Now, for pretty much all of the history of sushi, the idea of this being done by a machine was ludicrous, but you may want to take a peek at the video below. Behold – a robot with a silicon hand that can pick up squishy meat correctly, and put it on top of sushi! The idea was to have something that could save time. I doubt it’s economical, but it sure is nifty.
Incidentally, the meat that is put over sushi rice like this is cut in two and served in pairs, allowing the eater to appreciate the taste more (by being, well, less of a chore to handle). This is sensible. I just wanted to mention this to put the above video in context.