Crystal dagger

The Crystal Dagger is an item seen in the film Princess Mononoke. It is not used as a weapon.

Kaya gives the item to Ashitaka before he leaves his village. Later on in the story, Ashitaka gives it to San. Obviously the dagger is used to show the bond between two peoples. Kaya gives it to Ashitaka, because she wants to say, she will wait for him and she loves him.