Simone, born Simone Rolland (alternately Lorraine), starts as a 15-year-old flower girl in her adoptive parents Paul and Lillian Rolland's humble shop in rural Île de la Cité, France. Unaware of her adoption, she shares strong bonds with Parisian commoners and shows early compassion by pleading with Duke de Forges for her childhood friend Milan's release after his arrest for protesting noble oppression.

Following her adoptive parents' murder by agents of Madame Catherine, Simone learns of her adoption from her dying father. Duke de Forges takes her into his estate, enrolling her in an elite convent where she receives fencing instruction, eventually mastering a basket-hilted cavalry sword. Witnessing persistent injustices against the poor, Simone adopts the secret identity "La Seine no Hoshi" (Star of the Seine). This masked vigilante, wearing a domino mask, blue cap with a white star, and red cape, sabotages corrupt nobles, often riding a white stallion gifted by the Duke's son, Robert.

Simone's journey deepens upon discovering her true parentage: she is the daughter of Franz I, Duke of Lotringen, and an opera singer, making her Marie Antoinette's half-sister. This revelation clashes with her hatred for the aristocracy, especially the Queen. Despite the shock, she reconciles her royal blood with her revolutionary spirit, continuing the fight alongside Milan and the commoners. Her relationship with Robert blossoms into romance, and she occasionally allies with another vigilante, La Tulip Noire.

The story culminates with Simone marrying Robert and becoming stepmother to Marie Antoinette's children after the Queen's downfall, embodying a union between her commoner roots and royal lineage. Her arc transforms her from a sheltered flower girl into a resilient figure bridging societal divides while championing justice.