Ken Kaneki's father was an avid reader and had lots of books. He died when Kaneki was four years old, so Kaneki does not remember his face very well. Kaneki never felt lonely because his kind mother was with him.
However, Kaneki back then began to wonder what kind of person his father was. He started reading the books his father once had. It was strangely calming for Kaneki, and so were the scent of the old books. This is considered the reason as to why Kaneki began to like books so much.