Authority Equals Asskicking: The leader of Ange Déchu and the strongest member of the organization.
Ax-Crazy: Goes without saying. Even more than her need to take in blood in order to survive, she relishes in destruction and chaos, going so far as to admit surprise that one of her minions destroyed an iconic landmark and she didn't think of it first
Berserk Button: Being lied to.She permits a lot of insanely cruel actions from anyone in her organization, but trying to deceive her is a death sentence waiting to be carried out.
Establishing Character Moment: Her first appearance in the Phoenix Saga shows her supporting the destruction of the Seven Towers by Faer in the previous chapter, even showing a bit of jealousy that the thought hadn't crossed her mind at all beforehand. If one needed proof of her disturbed moral code, look no further.
From Nobody To Nightmare: She started as an idealistic woman. Then something happened in her past that not only resulted in her becoming an immortal monster but destroyed her innocence, creating the feared Queen of Blood that rules the Coven.
Lady of Black Magic: As if her being a vampire born of demonic powers wasn't a big enough clue. At the core, she is this, without the usual weakness of being physically weaker than her more masculine allies.
Meaningful Name: Myst is named for one of the Valkyrie, and her name is also Norse for Cloud. Her surname, Kagekyo, is actually a rather common name by the author, and the kanji ascribed to her full name is indeed indicitive of her character.
Mythology Gag: Ooh boy, where do we start? Every aspect of her character, her name, appearance, race, everything harkens back to the author's Bleach stories, starring a certain rose-haired bloodsucking badass with a dark empire to rule over.
The Don: A rare female example, Myst runs a crime empire that makes Al Pachino blush, and has been for decades, if not centuries.
The Thirty-Six Stratagems: Her debut reveals that though it wasn't by her hands, she already enacted at least six of them.
Valkyrie: See Meaningful Name above.
Woman in Black: Despite her vampish ways, she is very much this. Consorting with her is like wagering your very life against her finding use for you.