As you might already know, "Negi" in Japanese means spring onion, and "toro" is an expensive, fatty part of tuna. So you might think negitoro must have something to do with these. However, the origin of negi-toro has nothing to do with these. Negi is derived from the word "negitoru" which means to "scrape off". The word "negi" actually has nothing to do with the vegetable itself, and while it is true that negitoro is often served with chopped spring onion over it, the "negitoro" (minced tuna) part itself does not contain spring onion. The same goes with the "toro" part. Negitoro is not necessarily made from the expensive part of tuna. There are various theories as to why the word "toro" was added, but the most popular theory is that it is because it has a soft texture like toro. The most commonly used part of tuna for negitoro is nakaochi (中落ち), which is the extra flesh attached to the head, mid-bone, fins, and tail.