Gosick

Kujo Kazuya is studying abroad in Sovuria (a fictional country in Europe), where he meets the mysterious Victoria. Possessing a brilliant mind, which she calls "fountain of wisdom", she seems to know everything, although she never attends classes and is restricted to her room and the schools library. (Source: taken from the light novel summary) Note: Volume 2 contains the extra "Suigyo no Majiwari" (水魚の交わり).

Set in a fictional European country in 1924, a Japanese exchange student meets a mysterious, brilliant girl who only leaves the library to sleep. Her brother, a detective, relies on her mind to solve difficult mysteries, several of which draw her away from the library. With a drop of sweet romance, you will immediately become addicted to Gosick! *Note: GosickS is a series of side stories taking place before, after, and in between several of the cases covered in Gosick.*

Side story from Gosick.