Ashitaka is an 18-year-old Emishi prince who was meant to become the future leader of his tribe. One day, after rescuing his village from a demon (the Boar god Nago), Ashitaka received a fatal curse on his arm, which would eventually consume his body and kill him. The village shaman tells him that the Demon was corrupted by pain and hatred, and the source of the curse was an iron bullet found within his body. Ashitaka must go to the lands of the West to search for a possible cure, find out what is happening there, and finally "see with eyes unclouded". This means leaving his village forever because they have shunned contact with the outside world for 500 years.



Ashitaka arrives at Irontown, where he is caught up in a raging war between humans and the mountain gods. Ashitaka cannot take sides, as both sides fight for good and just reasons: humans to thrive and grow, the Mountain Gods for the right to survive.



Amidst this great battle, Ashitaka finds San, the Princess Mononoke. He falls in love with her at first sight, and he gradually wins San's love. Ultimately, he tries with all his might to create peace between the forest and man. Ashitaka's curse becomes a double-edged sword—it will eventually kill him, yet it also gives him supernatural strength, an ability which comes in handy at times. Ashitaka is also an excellent hunter, and could likely hold his own even without the curse.



At the end of the film, Ashitaka is freed from his curse and though San returns to the forest, he remains within Irontown, implying that the two will maintain contact despite living in separate worlds. He keeps scars from the curse.