Earthlings follows Natsuki, a girl who has strong beliefs that she is an alien, and has been sent to earth. This belief starts when she is a small child, and continues throughout her whole life. She struggles to fit in and sees a lot of societal norms, such as marriage and having children, to be ways in which the human race has been brainwashed. 

There are a lot of dark themes in this book, and I recommend going in with caution if you are a more sensitive reader, particularly regarding themes of child sexual abuse. 

I talk about this book in episode 44 of the Bookcast Club podcast. Episode link: 
https://www.thebookcastclub.com/podcast/episode/4ab9bc62/44-recent-favourite-author-discoveries