if i may suggest an idea you could say the elves come from an elven world that managed to fight off the monsters, but earth is the only other planet they found that hasn't succumbed to this evil so they sent civlians and warriors to help humanity survive.
23 days ago(+1)
Before I get into the project, I did try to ask for advice on lore building from my friend. And here are some of the options that I can choose from. Your idea could be suitable for the Old Testament or New Testament. And tbh that's not my intention because I don't think I have enough story building experience to make it a good story with full of plot twists or sth lol. But the idea of Elven people coming to help the earth is quite interesting. Especially when it comes to the language barrier which makes humanity think they are hostile >:) Oh hey I am somehow having new ideas while writing a reply to you hahahah. Thanks for your suggestion xD. Also the world story won't be too colorful but ofc not at Fear and Hunger level... right? (。_。)
it's okay if you try a few things before finding what is right, i just hope may be included in your projects as we see them too rarely in most medias. Also elves often help humans and are more advanced magically so they could fit well into this role, but it's a nice idea to have the humans think they are hostile at first