Stephen Turnbull , in " Nagashino 1575 " , relate the tale of the Takeda clan 's involvement with a fox @-@ woman . The warlord Takeda Shingen , in 1544 , defeated in battle a lesser local warlord named Suwa Yorishige and drove him to suicide after a " humiliating and spurious " peace conference , after which Shingen forced marriage on Suwa Yorishige 's beautiful 14 @-@ year @-@ old daughter Lady Koi — Shingen 's own niece . Shingen , Turnbull write , " was so obsessed with the girl that his superstitious followers became alarmed and believed her to be an incarnation of the white fox @-@ spirit of the Suwa Shrine , who had bewitched him in order to gain revenge . " When their son Takeda Katsuyori proved to be a disastrous leader and led the clan to their devastating defeat at the battle of Nagashino , Turnbull write , " wise old heads nodded , remembering the unhappy circumstances of his birth and his magical mother " .