GosickS

GosickS summary:

Set in a fictional European country in 1924, a j.a.panese 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!
GosickS is a companion series to Gosick, and fills in some of the gaps before and between Gosick volumes. GosickS I takes place before Gosick I, GosickS II between Gosick IV and V, GosickS III between Gosick VI and VII, and GosickS IV between Gosick VII and VIIIa.