Chloé d'Apchier entered the world in Gévaudan’s late 16th century as the daughter of a human noble house. Following the Babel Incident at age four, she transformed into one of history’s oldest vampires. Her father concealed her existence with strict rules: no unauthorized castle departures, concealed outdoor appearances, and absolute secrecy about her vampirism. Her aging halted completely by eleven, prompting the family to declare her death from illness—solidifying her role as their hidden vampire. Her father defied Catholic Church edicts by dedicating his life to researching the World Formula to restore her humanity. Subsequent generations continued this work, their motives shifting from familial loyalty to political ambition. Chloé alone witnessed this evolution across centuries as the family legacy’s eternal observer. August Ruthven became her first vampire acquaintance and close companion during research visits. Their bond shattered violently when Ruthven, altered by the Vampire War, demanded the World Formula Alteration Device—her family’s ultimate creation. Upon her refusal, he attacked, forcibly drank her blood, and tried to curse her into submission, though she resisted. Ruthven later tasked Chloé with caring for Jeanne, his student’s daughter. This prompted her first breach of confinement. She formed a deep sisterly bond with Jeanne, and their separation later devastated Chloé while broadening her worldview. Learning of Jeanne’s enslavement as a Bourreau decades later deepened Chloé’s isolation. As vampire hunts intensified in Gévaudan, the Catholic Church fabricated the "Beast of Gévaudan" to justify killings. Chloé discovered mutilated corpses during forest walks, eroding her mental state. After witnessing Church members murdering a woman, she reported it to Marquis Herman d'Apchier. His investigation caused his and his family’s deaths amid Church suspicions of vampire harboring. Herman’s daughter blamed Chloé and tried to kill her. During this turmoil, Chloé encountered Jean-Jacques Chastel, a young vampire abused by human parents. She took him in, and they became inseparable. Knowing the killings needed a scapegoat, Jean-Jacques surrendered his True Name to Naenia to become the Beast. When Jeanne arrived to slay the Beast—believed to be Chloé—Chloé attempted suicide by jumping from a height. Naenia offered survival for revenge, leading Chloé to willingly become a curse-bearer under the Malnomen "Millie, Theater of Ice and Snow." This curse forged an enclosed world from her memories, expanding to consume Gévaudan’s forests. It generated lifelike replicas of past figures, bound by Chloé’s perceptions. After a kiss from resurrected Vampire Queen Faustina, her curse escalated to its most lethal phase. She transformed into a formless mist-like entity amid floating terrain and black mist wolves, driven by self-destructive urges. Physically resembling a prepubescent girl with pale skin, large gray eyes, and short silver hair, Chloé’s expressions revealed mature depth. Her personality blended aristocratic duty with fierce protectiveness. As Marchioness, she upheld her father’s tenet that nobility meant protecting her domain’s people, maintaining love for them despite betrayals. She acknowledged her own jealousy and vengefulness, especially concerning harm to allies like Jean-Jacques. She exhibited curiosity about outsiders and mechanical aptitude, operating the World Formula Alteration Device with unrivaled skill. Her vampire abilities reflected ancient power. Despite her childlike form, she effortlessly overpowered adults and projected slashing energy attacks. The Alteration Device enabled reality manipulation, even manifesting Naenia. Curing her Malnomen required her conscious will to survive—without it, reversal meant death. Vanitas amplified his Book of Vanitas with his Mark of Possession to break her curse, highlighting Millie’s extraordinary strength. After her cure, she embraced her vampire nature over her father’s dream of restored humanity.