Rosalia de Catargena is a fellow candidate in the Sacred Bird Cosmos queen selection, competing directly against protagonist Angelique Limoges. Selected from the Royal Smallney Girls' Academy alongside Angelique, she undergoes the queen examination in the Holy Land. Her task, like Angelique's, is to cultivate her assigned continent with aid from the nine Sacred Guardians. Success in this competition hinges on gaining Guardian favor and developing her continent faster than her rival, forming the core premise of her initial role.

Her aristocratic background informs her noble demeanor and visual design, notably her Ojou ringlets. Despite the high-stakes competition, her interactions with Angelique lack overt antagonism; she maintains consistent respect and avoids bitterness throughout. This characterization steers clear of the "villainess" trope, as she remains amicable regardless of the selection's outcome.

Following the selection, her role evolves significantly across the franchise. Should Angelique win, Rosalia transitions into the position of the Queen's aide, serving directly under her. This supportive dynamic continues in subsequent titles including *Angelique Special 2*, *Trois*, and *Etoile*, where she consistently appears as a trusted supporter assisting the reigning queen with administration and cosmic stability. Her presence extends to the *Koi Suru Tenshi Angelique* anime, fulfilling duties tied to the Shinchō universe's throne.

Within broader franchise lore, including remakes like *Angelique Retour*, her core narrative remains unchanged: she competes as a queen candidate while prioritizing dignity and professionalism. Post-competition, her focus shifts entirely to supporting the cosmos' governance, whether visibly as an aide or through behind-the-scenes contributions. This consistent trajectory across games and adaptations highlights her maturation from candidate to an integral function within the cosmic hierarchy.