When I was reading Kafka on the shore I came across this theory wherein it's explained how people in the ancient times were made of components of two people, but then one day God took a knife and split them into two halves, people now spent their time trying to locate their other half this reminded me of the kindered spirits theory in Anne with an e so I thought why not make a list of books that I think suit the theory. You can make your own suggestions in the comment section :)