Just a concept sketch that needs work.

Sato Tadanobu was a retainer for Minamoto no Yoshitsune (adult Ushiwakamaru) who, at one point, disguised himself as Yoshitsune inorder to distract their enemies and allow his master to get away. Inorder to do this, Sato wore Yoshitsunes armor and brandished one of his swords, fighting off the enemies as best he could.

Meanwhile, Genkuro was a white Kitsune who helped Minamoto no Yoshitsunes lover, Shizuka Gozen, aiding in her escape and appearing to her and Yoshitsune as his retainer, Sato Tadanobu. Genkuro was extremely loyal to both Yoshitsune and Shizuka and simply wished to obtain a drum Shizuka had which was made with the skin of Genkuros parents.

Also also, Sato Gozen was Minamoto no Yoshitsunes legal wife. A lovely woman who was married off to Yoshitsune as part of a political engagement arranged by Yoshitsunes brother and Satos parents. After Yoshitsune brother decided to have him killed, however, Satos entire family was murdered by association and Sato herself, in one telling, was mercy killed by Yoshitsune inorder to prevent her from being captured and tortured by his brother.

Now, my thought process was, what if Sato Tadanobu, Genkuro, and Sato Gozen, were all the same person, kind of? 

Sato, who was always a kitsune, goes into hiding after her family was killed and transforms into a white fox. She reacuse Shizuka Gozen and appears before her and Yoshitsune as Yoshitsunes missing retainer, Sato Tadanobu. Sato then wears Yoshitsunes armor, distracts the enemy, and later revealed herself as Genkuro with almost nobody knowing she was Sato Gozen, Yoshitsunes assumed dead wife.

Fanservant wip: Pretender Sato Tadanobu/Genkuro