More Info: https://www.doujinshi.org/book/715908/fairy-dance/
Artist Deleted their Pixiv, as well their blog and disappeared from the community. If anyone has any info regarding the artist please share. I hope they safe and well.
Dolphinslow - Yep you are right, Muse is an spirit, created by lord maxwell itself, so much that is the only thing that Milla can actually call an sister wich actually happened on the story.