Songs/poems like this are extremely hard to translate due to nuance and subtle meanings hidden to context. If you translate the words directly you end using words that misrepresent the intended meaning of the word. I think it is extremely important for this song to be properly translated since it adds another depth of beauty to the movie. I was not satisfied with the already existing translations so I decided to write one myself. I am Japanese but I have been living in the US for 15 years and I am fluent in both.

Mononoke means spirit beasts in the context of the movie. Examples of mononoke being Moro the Wolf Deity for example. The term "princess mononoke" is the nickname given to San, the female protagonist, due to the fact that she is a human adopted by the beasts.

This song is how Ashitaka, our main male protagonist, views San in his mind; someone whose beauty compares to that of a dangerous weapon. It's the tale of forbidden love between two clashing worlds.

This song plays while he is in the cave home atop the mountain of Moro the Wolf Deity where Ashitaka has a discussion about San's future. Ashitaka wants to save San as a human, for his own reasons, but Moro wants San to fight and die as a beast. Ashitaka adamantly argues with Moro but he himself already knows that San's heart lies with beasts and forest.

I think the song is trying to convey that Ashitaka realizes he ll never be the same or fully empathize with San. Ashitaka sees good within humanity despite the destruction they can cause while San is unable to; Ashitaka is a human who is human at heart. San is basically a weapon, a very sharp weapon, that is pointed to humanity which includes himself. I think the fact that he is comparing San's beauty to that of a weapon realizes this and is indicative of his internal conflict of trying to save someone that is against humanity.