Sasuke lives with his sister in the mountains of Shinano. Their only friends are the animals in the mountains. Eri, a baby deer, is kidnapped by a giant eagle and dropped into a deep and dark lake. The mother deer chases after her and jumps into the lake, where she transforms into a monster salamander, devouring her victims. When Sasuke struggles with the salamander and sticks his sword into the monster’s mouth, it strikes and fells him with a single blow. The true identity of the salamander is the sorceress Yashahime. Sasuke must acquire the skills of ninjitsu in order to defeat Yashahime, and he is accepted as a pupil by the master Hakuunsai on mount Togakushi. After rigorous training, the mysteries of ninjitsu are revealed to Sasuke and he is ready to descend the mountain. On his journey, he encounters Yukimura Sanada, a young lord of Ueda Castle, in pursuit of bandits who are raiding the area. The bandits have joined forces with Yashahime. Sasuke joins Yukimura to drive out the bandits. Sasuke’s sister Oyu is taken hostage, and Sasuke is severely beaten by Yashahime, but Yukimura rescues Oyu.