She is the evil witch that is trying to get Elde's key that Souta has. Her real name is Marlene. In the beginning she was good, but ever since the boy she liked from Elde had to go back she started to hate the concept of two worlds. Her hatred grew when one day she found a way to get to Elde and saw through the mirror that the person she liked was now with another girl. This led her to aim for dark magic and get revenge on god. Her final transformation to Cenderillon happened when the boy she loved came back to stop her, got in the way of an attack and died.

(Source: Wikipedia)