The legend of Kogitsune-maru states that it was forged by an unspecified nature spirit. Many variations tell the story of a wily kitsune who used her forge work as an escape for the terminal boredom of the world before the arrival of people, while others place the responsibility for its creation upon either a tenuki or even a greater kami. No proper name is ever provided.
In most tellings of the associated legends, the blade was forged as a form of supernatural prank that backfired upon the blades creator. Whether this took the form of the wielder accidentally killing the creator, or someone stealing the blade only to find it cursed and killing someone very important to the creator, ill fortune always lands at the feet of the individual who forged it. After this discharge of ill fortune, the blade becomes endowed with the power to grant great fortune to the person who wields it.
Another legend of Kogitsunemaru is that it was forged by Sanjo Munechika, the same creator of Mikazuki Munechika. Sanjo Munechika had the help of the fox god, Inari, in the form of a little boy when he came to Fushimi. With the inhumane skill of the god, he created another masterpiece and dedicated it to the god. Kogitsune means little fox.