Queen Nehelennia originated as Queen Helenia, ruling a kingdom renowned for peace and her subjects' adoration of her beauty. Her obsession with eternal youth ignited upon seeing her aged reflection in a mirror. To preserve her appearance, she forcibly extracted her subjects' dream mirrors, transforming them into Lemures, and manifested Zirconia from her own fears of aging. Consumed by envy of the Moon Kingdom's prosperity, she plotted to usurp Queen Serenity and seize the Golden Crystal from its guardian, Helios. Queen Serenity thwarted these evil intentions by sealing Nehelennia inside a mirror during Princess Serenity's birth celebration. Before imprisonment, Nehelennia cursed the Silver Millennium to fall and the princess to die before inheriting the throne. During a solar eclipse depicted in *Sailor Moon Eternal*, Nehelennia partially breached the mirror seal. She corrupted Sailor Chibi Moon's future guardians, the Sailor Quartet, brainwashing them into the Amazoness Quartet to serve her Dead Moon Circus. Nehelennia commanded Zirconia to spread nightmares on Earth, targeting the Sailor Guardians' insecurities to weaken them and seize the Silver Crystal. She invaded Elysion, cursing it and imprisoning Helios, though his spirit escaped as Pegasus. Discovering the Golden Crystal resided within Mamoru Chiba, Nehelennia intensified her efforts to capture it. Nehelennia possessed long, flowing dark hair (depicted as blue or black across adaptations), pointed ears, and wore elaborate attire featuring spiderweb-patterned cloaks and crescent moon jewelry. Magic from the mirror sustained this youthful form; when the mirror shattered, she reverted to a withered, aged crone resembling Zirconia. In the Elysion climax, Nehelennia deflected Sailor Moon's attacks and trapped the Guardians in a kaleidoscopic dimension, forcing them to relive her past confrontation with Queen Serenity. She seized the Silver Crystal and nearly killed the Guardians, but the bond between Usagi Tsukino and Mamoru freed them. Empowered by the combined strength of the Eternal Sailor Guardians and Mamoru's Golden Crystal, Eternal Sailor Moon destroyed Nehelennia and her mirror with Starlight Honeymoon Therapy Kiss. Nehelennia disintegrated into sand, lifting the curses on Earth and Elysion. The manga and *Sailor Moon Cosmos* reveal her as an incarnation of Chaos, alongside entities like Queen Metalia and Pharaoh 90. In the anime's fifth season (*Sailor Stars*), Sailor Galaxia freed her from the mirror to exploit her hatred of the Moon Kingdom. Nehelennia shattered her own dream mirror, infecting Earth with its shards, and kidnapped Mamoru. Sailor Moon ultimately forgave her, granting her wish to restart life as a child. Her abilities included casting potent curses, corrupting beings, manipulating nightmares, controlling barriers, teleportation, and projecting illusions to trap adversaries in dream worlds or glass prisons.