Diana, the Strong-Willed Princess (or the Dutchess), another character from the game Rule of Rose.
Looking at all the fanarts, cosplayers, etc, I’m quite sure she’s everyone’s favourite crazy girl. Deep down inside, we’re all attracted to the most cruel, heartless and sarcastic characters from the games we play - and it’s no different towards RoR.
From Rule of Rose Wiki:
She is very devious and cruel, even toward the other members of the Aristocracy. She often adopts a nonchalant attitude and is uncaring of the thoughts of others. She is the object of affection for Meg, and seems to be the eldest of the orphans.