Caterina, sometimes spelled Catherine, acts as a primary antagonist throughout most of the narrative. As the eldest daughter of Duchess Danton and older sister of Jeanne, she becomes Cinderella's stepsister after her mother marries Duke Foyer, sharing the same household.

She possesses brown hair, blue eyes, and fair skin, with a distinguishing mole beneath her left eye, and stands slightly taller than most women her age. At home, she typically wears a simple blue dress and brown shoes, but favors dresses in shades of orange for formal occasions.

Caterina's personality is marked by cruelty, condescension, and a lack of empathy, especially towards Cinderella. Spoiled by her mother, she exhibits a strong preference for luxury. Her driving ambition is to marry Prince Charles, motivated solely by the desire for status, wealth, and power as a princess. She consistently ridicules Cinderella's appearance, burdens her with excessive labor, and ensures her life remains difficult, showing no reciprocation for Cinderella's kindness. Caterina is embarrassed by her public association with her stepsister and mistreats others she deems beneath her, including mistaking the disguised Prince Charles for a common servant and boasting she would employ him in the castle kitchens once she married the prince.

Within the household, Caterina actively enforces Cinderella’s servitude alongside her mother and sister, starting after Duke Foyer departs. She helps evict Cinderella from her bedroom to the attic and imposes all cooking, cleaning, and household tasks upon her.

Specific instances highlight her behavior:
* She and Jeanne participate in the Flower Queen contest hoping to attract Prince Charles.
* She ridicules Jeanne’s eating habits and mocks her need for larger dresses.
* She joins her family coercing Cinderella into inviting the disguised Prince Charles to glean information about his preferences for a wife.
* She becomes infuriated when Cinderella outperforms her and Jeanne in dancing lessons.
* She attends Duke Zarel's daughter Isabel's birthday party solely due to the potential presence of Prince Charles.
* She derides noble daughter Lora for eloping with a commoner violinist.
* She and Jeanne are manipulated by Duke Zarel into spying on Prince Charles at Emerald Castle, assigned maid duties they delegate to Cinderella. A subsequent fight destroys a royal porcelain doll, resulting in their dismissal.
* When Cinderella falls ill, Caterina and Jeanne complain about helping with chores until their mother forces Charles to take over; Caterina boasts to him about marrying the prince and offering him and Cinderella jobs.
* She participates in framing Cinderella for losing a mint pearl ring, knowing Jeanne took it, and mocks her when she returns the found fake ring.
* She hits a bandit with a chair during a home invasion by Zarel’s men.
* She and Jeanne wear simpler dresses temporarily as part of a scheme to present Cinderella as engaged to Flora Melville, later informing Charles of this false engagement.
* She shows genuine concern for her mother when Danton falls seriously ill.
* At the royal ball, she and her family mock Cinderella's dress, destroy her invitation, and leave without her. They fail to dance with Prince Charles and become jealous when the magically transformed Cinderella captures his attention.
* During the glass slipper test, she forces her foot into the shoe, causing pain before it pops off; afterwards, she and Jeanne blame their mother for their large feet.

A significant shift occurs after Cinderella’s engagement to Prince Charles. Caterina abandons her vain, selfish, and lazy disposition, ceases idling, establishes peace with Cinderella, and departs from her previous antagonistic behavior. Before this conclusive change, the series depicts fleeting instances where she, her mother, and sister showed remorse or seemed to learn moral lessons, only to revert to mistreating Cinderella.

As the oldest sibling, her relationship with Jeanne involves occasional mockery, particularly about Jeanne’s eating habits and physique, though they typically present a united front against Cinderella. Her interactions with her stepfather, Duke Foyer, involve superficial displays of care that vanish once he departs, revealing true indifference.

Her narrative function centers on antagonizing Cinderella and contributing to her hardships, a role persisting until the final reconciliation following Cinderella's engagement.