Nenia functions as a primary antagonist, an ethereal entity who inflicts Malnomen upon curse-bearing vampires by stealing their True Names. She operates with the enigmatic organization Charlatan, facilitating the creation of curse-bearers for undisclosed purposes. Her actions directly oppose Vanitas and Noé Archiviste's quest to cure afflicted vampires, driving persistent conflict.

She manifests as an unstable shadowy figure composed of dark energy speckled with white particles, marked by a cracked, luminous eye and an unnerving smile. When stabilized, she assumes the form of a young woman with large, round eyes and long white hair. Malice defines her personality, coupled with a singular obsession for hunting True Names, showing utter disregard for others' sanity or safety. She views figures like Noé Archiviste and Chloé d'Apchier as mere playthings or tools. Chloé once trapped Nenia in retaliation for corrupting Jean-Jacques Chastel, attempting to kill her, but Nenia escaped.

Her true identity is Naenia, She Who Harbors Death—the Malnomen of Faustina, the Vampire Queen of the Crimson Moon. Faustina, recognized as the first vampire of the red moon, is implied deceased or near death, her existence concealed. Nenia is Faustina's corrupted manifestation, directly linking her to the origin of vampire curses and establishing her as a Monster Progenitor.

Nenia manipulates minds, entering vampires' psyches to read memories and induce vivid hallucinations of their deepest fears or desires, enabling her to steal True Names. She alters these names to inflict Malnomen. Her influence extends to physical and environmental manipulation; her destabilization during the Gévaudan incident fractured reality, causing the Château de d'Apchier and its surroundings to collapse into fragmented, floating debris after she violently forced Chloé d'Apchier's Malnomen to onset.

Through Charlatan, she deploys spectral performers and clowns spreading madness via maniacal laughter, summoning them during hunts like the Gévaudan confrontation. Her departure often leaves witnesses trembling under lingering influence. Her origins tie into the German Faust legend, reflecting dissatisfaction leading to destructive pacts. Her name derives from Latin, meaning a funeral dirge, enchantment, or lullaby, connecting to Nenia Dea, an ancient Roman funeral deity, and references a genus of moths symbolizing decay and transformation.

Historically active during the Babel incident—which altered world laws and created vampires—she resurfaced in Paris with Charlatan's parade. In Gévaudan, she temporarily stabilized by possessing Faustina's form, appearing nude with Godiva Hair, and delivered a Kiss of Death to Chloé. This triggered the catastrophic expansion of Chloé's Malnomen, nearly consuming Gévaudan within a sealed space. Her existence remains a destabilizing force tied to the Queen's lingering power, perpetuating conflict through her relentless hunt.