Ashitaka is the last prince of the Emishi tribe. The Emishi's are a tribe of people who been banished from the west of Japan. One day, his village was attacked by a demon boar and when he was saving his sister Kaya from the monster, the blood worms wrapped themselves around his arm as he tried to defeat it. Later at the Oracle's hut she told him that it was a boar god named Nago who had been shot with a iron ball and therefore turned into a demon boar. Since Ashitaka was cursed by the worms, the Oracle informed him that the poison will seep into his bones and he will die. The Oracle then told him that he needs to go to western Japan in order to find a cure to lift Nago's curse however, in the law of the Emishi tribe, Ashitaka must be banished and to never set foot in the village again because the people would accept that he is "dead".
When he was about to leave, Kaya gave him her crystal dagger to him as a reminder of her when he leaves. Shortly after, he left the village and journeyed to the west.
He talks little but has a great sense of justice and would do anything to save San and to lift the curse on his arm from spreading and to stop the war between the humans and the forest god's of the forest. He cares very much for San since he loves her and only want's to try to help her.
San - When he first saw her he was struck down by her fierce beauty and strong will, and he wants to share half his life with her and after the Forest Spirit got his head back and finally rest in peace. San finally admitted that she does love Ashitaka and he mean so much to her, however she could not forgive the entire human race for destroying the forest and still continues to live part of the forest with her wolf brothers Yama and Moru. Ashitaka promised her that he will visit San in the forest as soon as possible while rebuilding Iron Town.
Kaya - Actually Ashitakas Bride-to-be (Hayao Miyazaki states this) and therefore cares very deeply for her, as she does to him. Before he left the village, Kaya snuck out and gave him her crystal dagger which she holds dearly. Another time where he showed his care for her was when he saved her from the raging demon god.
Moro - It seems that Moro has a deep hatred as much as San does and she told him about how se found San as a baby and told him to leave at sunrise and when they meet again she would kill him but when Moro was saving her daughter from the bad Lord Okkoto she said that can she save the girl he love which was San and was Moro was finally avenged by Ashitaka.
Lord Okkoto - It's unknown if they're friends or not but when they first met Okkoto explained that he is only grieved and ashamed for a demon like Nago came from his tribe and he thanked him for telling the truth of what happened to the demon boar but when he asked Okkoto if there's anyhing that he can do to lift Nago's curse Okkoto only said is to leave the forest alone and for the next time they meet he will have to kill him.
Lady Eboshi - It's unknown but when he met her but she told him that when the forest are cut down and the trees cleared, this land will be the richest land in Japan but after the war between the forest god's of the forest Ashitaka would go back to IronTown and help rebuild it and make it a better town.
Bow and arrow - He is very skilled with the bow and arrow as he could kill samurais on horses from several meters away.
Sword - Though he doesn't use it much, it is shown throughout the film that he can defend himself with a sword and throw it with great accuracy.
Demon Strength: More of an unwanted ability, after encountering Nago, Ashitaka's strength grows tenfold.