She died at a young age, and years after her death, it is revealed that she perpetrated a crime that caused the disappearance of one of the most elusive thieves in Europe, Kuiaran.
Millie is a young girl with wavy blond hair and blue eyes. Her hair reaches to her back and two locks of her hair hang from either side of her face. Because of her terminal illness, she has a pale complexion compared to her classmates.
She is usually seen dressed in the uniform of Saint Marguerite until the time of her death, where she wears a white dress.
Roughly eight years before 1924, Maxim arrives at Spring as part of his usual visits in Saint Marguerite as a graduate of the said academy. In one encounter, Millie falls in love with Maxim after receiving a bouquet of primroses from him. However, she realizes that her illness will give her little to no time to express her love for him, so she decides on an elaborate plan to seize Maxim's affections.
The crime Millie Marl committed was discovered by accident by Kazuya, Avril Bradley and Cecile Lafitte along with two crypt workers. Upon opening the doors to the crypt that has been left closed for eight years, a corpse of a man dressed in a knight's armor is discovered. This initiated an investigation by Inspector Grevil de Blois, who later identified Maxim as the corpse.
Victorique de Blois later linked Millie Marl to Maxim's death, and she revealed the story of the unrequited love that Millie offered to Maxim even in her death.
At the time of the incident, Millie utilizes a substance that puts Maxim to sleep and dresses him in the costume of a Knight Templar, placing a small bunch of primrose flowers on his chest. She then conceals his location by disposing one of the corpses inside the crypt (she steals the keys to the crypt beforehand) and replacing it with Maxim's body.
Several days later, Millie passes away, and her remains are taken to the crypt. In accordance to her plan, Maxim dies along with her inside the crypt, and she makes certain that they would never be apart, as the primrose flowers symbolize.
- Millie's citizenship might be British, as both her name and surname are British in origin.
- Millie is, in fact, Cecile's classmate from her days in Saint Marguerite.