An Unagisaki Hocho (Japanese: 鰻裂 or うなぎ裂) knife is a special Japanese knife for filleting eel.
The blade would be rectangular, except its nose is a straight 45 degree angle from top to bottom. This creates a sharp tip or piercing the head of an eel, and then dragging the knife along its body to slice it open along its entire length in one continuous motion.
The blade style varies slightly in Kyoto, Nagoya and Osaka.
“Unagi” means “eel”; “hocho” means “knife”.
Japanese Kitchen Knife Types And Styles. Accessed October 2019 at http://zknives.com/knives/kitchen/misc/usetype/all/index.shtml