Dantalian no Shoka

The young man Huey took over the old mansion of his deceased bibliomanic grand father as well as the book collection that's stored in there. But there was a condition: he also had to inherit the "Bibliotheca." When he inspects the mansion, Huey discovers a cellar filled with piled up books. In the midst of them he comes across a black-dressed girl who's silently reading a book. She's called Darian and has a big lock hanging in front of her. She herself is the entrance to the "Bibliotheca of Dantalian" which contains the prohibited "Phantom Books." (Source: MyPersonal-scan-)

A mystery at a prestigious girls' school draws together Dalian and Priscilla, an impoverished aristocrat's daughter. As they attempt to solve the mystery concealed by the school, Dalian gets to experience "every day school life"