EirSongwood
Diana is trapped in the Night World with her mysterious captor, a vampire she calls "the Monarch" because of his amber, butterfly-like wings. Diana learns key details about the monarch through his servants and friends, and her goal becomes getting back to the Sun World, a place which is a distant dream to her memory. Yet the Night World is calling, familiar, comfortable. Will Diana be able to come back and explore, or will her heart return to the Sun World, the place of infinite light and beauty?
This was originally a Kindle Vella, but that got discontinued. The story will start from the beginning here.