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).