What is this thing?

Marubi would be the romanized spelling of the Japanese word. Marbee is probably anglicized.

In hiragana the word would be written as まるび.

Given how maru can be used in Japanese when preceding another word I'm guessing Marubi translates to Maru = Best, Bi = Tool for BestTool.

I have several. The orange handled ones are likely most similar to Knipex. These are much more clunky though. They are good for many things and are much more sturdy for things like house wiring. The ones I asked about in the post are much smaller feeling in the hand. They feel like a precision tool unlike any other side cutters I have used. I can strip enamel off of magnet wire with just the hand feel of these when they are sharp and new. The ultra thin handle profile just works in really tight spaces, like putting my index finger on the rivet to hold the jaws on the flat surface and fingertip touching the handles together without gripping the handles. They feel light and well shaped like this type of mobile dexterity was by design. The guy that gave them to me only had very high end tools and was out of Europe.

Bottom row are super useful. I almost never use the tops