One of my favorite books as a kid was The Selkie Girl by Susan Cooper. Her Dark Rising series was one of my favorites as a kid and this feels very at home in that. Overall I think a little more detail on Selkies, some tables of events etc would help flesh this out a bit, but I understand operating within the one page RPG format leaves a lot unsaid. I do love the Tarot deck guiding which you have to pull as a way to make the whole thing more challenging as well.