Please keep it with you, brother, to protect you. You must take it with you, please, I want you to have it. So you won't... forget.
- —Kaya's final words to Ashitaka, regarding her crystal dagger.
Kaya is a young human girl in the movie. She has brown hair with a single red bow pigtail and brown eyes. She wears a purple kimono with red lining and a straw hat.
At the beginning of the movie, Kaya is seen with two other girls warning Ashitaka about something they saw in the forest. Next, she is seen sprinting down a hill with the same two girls, running from the demon; one of them trips, and Kaya pulls out her dagger to defend them. Ashitaka soon saves them from the demon by shooting an arrow in its eye.
Kaya later appears to goodbye to Ashitaka when he is forced to leave the village (despite the rules that forbid it) and gives him her crystal dagger to remember her by. Because of the curse, he is unfortunately banished from his home. She is never seen or mentioned after this.
Ashitaka later gives Kaya's dagger to San, the wolf girl which could be seen as several meanings. One that he was willing to pledge loyalty to San; despite being a human or formerly engaged. Or that it was to symbolize how much San meant to him as once upon a time Kaya meant to him.
Though she calls Ashitaka "brother" (jap. anisama), she is actually his bride-elect. The word means "follower" because they live in the same village.
When Ashitaka leaves his home in the night, she approaches him to say goodbye. However Emishi tradition forbade her to do so. She gave him her crystal dagger. In Emishi tradition girls gave a dagger to their future husband on the day of their wedding. However, Kaya's act showed her love for Ashitaka.
Kaya is a syllable of the Japanese word Kusa no Kaya, a well-known knife as a lucky charm in Japan.