She was portrayed by Emilie Dequenne.
The beautiful and modern young noblewoman Marianne de Morangias lives in the areas of Gévaudan with her parents the Count and the Countess of Morangias and her protective brother,an one-armed hunter Jean-François de Morangias. She quickly catches Knight Grégoire de Fronsac's eye and immediately falls in love with him.
When the attacks are mutiplying in Gévaudan, she also followed by her mother and her brother Jean-François, jealous of her relationship with de Fronsac. She decides to leaving her family for Grégoire, one night the Beast attacks them but unexplicably spares Marianne and leaves. Later days, Grégoire is arrested and dying and Marianne, doubts of his guilty, suspecting the noble of Gévaudan for killing him. The local priest Henri Sardis wants to kill Marianne in empoissoning her milk, she nearly drinks it but she's stopped by her brother Jean-François, who's revealed being the Beast's master and having incestuous feelings for his sister. She's raped and left for death by him.
When Grégoire kills Jean-François in a single combat and the secret society, the Wolves of God, whom members are revealed being gypsies and many noblemen (including her mother and brother), headed by Henri Sardis are arrested, Marquis Thomas d'Apcher informs Grégoire that Marianne is dying. He found her alongside her father, he tell her that he loves her. He saves her with pounder with his Indian deceased friend's bracelet.
Later, Grégoire and Marianne departed to Africa together and lived happily ever after.