Rosaria is a treasure hunter specializing in salvaging underwater relics. Despite occasional valuable discoveries, financial hardship persists as buyers hesitate to pay premium prices for artifacts with rightful owners. Her work involves diving operations to recover these items. She encounters Fujiko Mine suffering from amnesia after an accident and takes her in, offering shelter. Rosaria develops a protective role, shielding Fujiko from pursuers seeking the memorized Columbus Files, which reveal the location of the Columbus Egg treasure. Rosaria's connection to the Columbus Egg originates with her father, Barton. He researched the orgone energy within the artifact, initially seeking a cure for the illness that killed Rosaria's mother. Barton's motives later corrupt, shifting towards weaponizing the energy for world domination. Discovering his betrayal causes Rosaria profound shock and revulsion. She condemns him and attempts to stop his plans, including an unsuccessful effort to kill him. During the confrontation with her empowered father, Lupin III intervenes to save Rosaria. Following Barton's defeat, Lupin returns Barton's locket to her. The locket holds a childhood photo of Rosaria and an inscription: "My dear daughter, with love." This act signifies Lupin's acknowledgment that her cherished memories of Barton as a loving father remain valid despite his later actions. Rosaria demonstrates combat proficiency, particularly with a knife, though distractions during fights occasionally leave her vulnerable against adversaries like Nazaroff. Her dynamic with Fujiko includes moments of protective intimacy and lighthearted suggestions about "sharing" Fujiko with Lupin, reflecting their complex rapport.