If you want to filet fish the Japanese way, you need a deba. It's a hefty knife with lots of steel to withstand fish bones. The single bevel is designed to get the edge closer to the action and also to keep you from dragging the surface of the blade over all your beautiful fish meat.
About the shape
Deba means “short fat tooth” and this describes the shape of the knife. This is the first knife a sushi chef would use when preparing fish. It is used to fillet fish and butcher the boneless meat. The Deba is a traditional Japanese blade that is only sharpened on one side. This is called “single bevel.” Don’t let the shape and weight of a Deba fool you; they are nimble and precise. Choose the length of your Deba based on the size of fish you’ll be butchering most often.
About Tojiro: Tojiro is a knife-making giant in Japan. While they have a small factory that produces incredible hand-forged knives, their true specialty is factory-made knives. In Japan, “factory-made” isn’t what most people think. While the blades are rolled and stamped, much of the work is done by hand including grinding and finishing steps. Tojiro primarily works with VG-10, a stainless steel loved for its ease of sharpening and easy maintenance, but they also use VS2, SK85 and others.