Princesa Rosa serves as the central princess of her kingdom. Her father, the King, issues a decree that she must marry whoever proves to be the richest and bravest suitor, initiating the main plot.

She demonstrates compassion and moral conviction. Introduced treating the poor miller's son Pierre, posing as nobility, with kindness and warmth, she later rejects the marriage ultimatum of the ogre sorcerer Lucifer, refusing despite his threats to destroy the kingdom. Her demeanor remains gentle yet resolute during these confrontations.

Her role shifts dramatically during the conflict. After refusing Lucifer, he kidnaps her directly from the castle as his three-day deadline expires. Confined in Lucifer's lair, she witnesses his terrifying transformation into a three-headed dragon, an event causing her to faint from shock and fear during the subsequent rescue attempt.

Her relationship with Pierre evolves from initial courtesy into mutual affection. Despite Pierre's early deception about his identity, her appreciation for his genuine kindness endures. Following Pierre's participation in her rescue alongside Pero and mouse allies, she openly reciprocates his feelings. This union concludes her arc, transitioning her from a political bargaining chip to an active participant. After Lucifer's defeat, she marries Pierre, elevating him from poverty to royalty and securing her own future within the kingdom. Her story concludes with this journey from betrothed princess to rescued figure and finally to Pierre's consort.