 The eruption of Mt. Fuji in 1707 released hordes of demons from deep inside the earth. Sakuya, the young daughter of a samurai killed fighting these demons, accepts a mission to travel to Mt. Fuji and defeat the evil spirits. Accompanying her on her journey are two veteran warriors who served her father, and Taro, a young kappa, or river spirit, whom she has adopted as her little brother. Along the way, the two warriors have doubts about Taro s loyalties, and the young kappa himself must decide if he will stand with his own species or with the humans who have cared for him.