I think Na-in was human and Amon fell in love with him, killed his people to have him and with the help of the priests made him some kind of god so they can live together forever. Which may be why they do those human sacrifices and the priests aren’t as respectful of him because he wasn’t a God originally. I think why Na-in is originally depressed and was scared of Amon is because his subconscious mind know what Amon did to him. And in the hypothesis that he was a god too, I think he was a peaceful god who lived in harmony with humans and Pink hair was one of his people.