Dantalian no Shoka

Alternate title: The Mystic Archives of Dantalian

Dantalian no Shoka is a fantasy anime based on the light novel written by Gakuto Mikumo and illustrated by G-Yuusuke. The anime series, which consists of 12 episodes, began airing in Japan in July of 2011.

The premise: when his grandfather is murdered, Hugh Anthony Disward finds himself the heir to a large estate housing a huge library. When Hugh (or Huey as they call him) first arrived at the premises, he was totally oblivious to what was about to happen to him.

Among the thousands of books is a beautiful young girl clothed in black, and she is reading. Her name is Dalian. As it turns out, she controls the gateway to the Bibliotheca Mystica de Dantalian, the forbidden books of demonic wisdom. These are prohibited books that endanger the balance of the world. Hugh inherits the key to the Dantalian bookshelf and along with Dalian, they solve mysterious (and sometimes gruesome) cases involving these dangerous books.

If you were a fan of Gosick, then you'd probably enjoy this anime as well. The genre is very similar..ie: Loli detective.