Tenshi No Hitsugi summary:

This story set in Europe 1889, is about a young girl named Marie Alexandrin who is a normal, innocent blond with an immense crush on the good looking Crown Prince Rudolf. On a trip to the library with her mother, she manages to accidentally liberate a handsome young magenta haired demon by the name of Set from an old book in which he had been sealed, and as a thank you he decides to do something for her - whatever she wishes....Extra Stroy: One Snowy Night