Roppyaku Peiji no Mystery

Roppyaku Peiji no Mystery summary:

Asami is a girl who adores reading books in an old library in her hometown, almost as much as the person who works there. That person is the librarian Mizushima-Sensei, who is quite unusual, but also very popular because of his young age. When someone begins to write graffiti in the books Asami loves most, it seems there’s trouble within the small library. Can their love of books and the dream of a wonderful library bring these two characters closer together?