Maryrose stands out among the Shadows House's silhouette residents with her distinctive appearance: a completely black form dressed in a frilly white high-collared shirt, purple corset patterned with white rose line art, short pink skirt, dark-green puffy breeches, and white high-heels adorned with purple roses. Her long braided hair is secured by a rose clip. Exhibiting an outgoing, dependable, and dramatic personality often perceived as gallant, she is the most senior shadow in the Children's Building, looked up to by younger shadows. She enjoys dancing and teaches it to others like Kate.

Uniquely, Maryrose retains memories from her existence as a morph before mimicking a human. This awareness fuels her rejection of the Shadows House's brainwashing practices and her opposition to the forced unification of shadows and living dolls. While maintaining a facade of compliance with the hierarchy, she secretly resists. Her physical-type soot power allows remote control of small, light objects, creation and manipulation of scorches, and merging scorches into a phantom if they exceed a certain threshold. Absorbing other shadows' soot increases her scorch count. This ability, recently re-awakened, was used to orchestrate incidents, creating phantoms to test her powers and expose those with "unnecessary thoughts."

Maryrose shares an exceptionally close bond with her living doll, Rosemary, treating her as an equal. Together, they evade the brainwashing coffee and collaborate on plans to undermine the house. Their relationship defies the master-servant dynamic through mutual devotion and synchronized actions.

Rosemary serves as Maryrose's "face," filtering soot and maintaining the human illusion. She has long brown hair in a loose braid with a blue bow and red eyes, dressed in a Victorian-style maid outfit with dark sleeves, a white apron, and skirt. Rosemary acts as a kind, motherly figure to her team members Emilico, Mia, and Lou, demonstrating predictability and reliability. She actively participates in Maryrose's resistance. During a phantom incident, Rosemary was attacked by a scorch, suffering soot sickness before recovering. The Star Bearers later blamed her for the incident, dismissing her explanations.

Their background involves Maryrose and fellow shadow Barbara promising to "become adults together" after debuting. They admired senior shadow Christopher, whose educational initiatives elevated the children's reputation. However, after Christopher was invited to Lord Grandfather's wing, instructor efforts waned, distressing Barbara. Maryrose withdrew upon learning from Christopher's doll, Anthony, about fusion – the assimilation of living dolls – and Christopher's subsequent suicide. This trauma led Maryrose to reject becoming an adult, deepening Barbara's despair and triggering a soot explosion that injured Barbara's doll, Barbie. Barbara later became Star Bearer leader under Thomas's intervention.

In their final arc, Maryrose and Rosemary are captured after her rebellion is exposed. Edward deduces Maryrose possessed inside knowledge of fusion. Cornered in the Passage of Glory, Maryrose creates a phantom to attack Edward, who retaliates with sound-manipulating soot power. Facing forced unification or execution, Maryrose and Rosemary share a smile, embrace, and leap from a high tower window. Kate attempts to cushion their fall with soot; their survival remains unconfirmed. This act symbolizes their ultimate defiance and refusal to be separated.