Echidna, the Witch of Greed, possesses a complex existence. Her appearance features porcelain-white skin, long straight white hair reaching her back, and striking black eyes that sharply contrast her pallor. She typically wears modest black clothing enhancing her monochromatic aesthetic, though she once manifested in a Japanese school uniform drawn from Subaru Natsuki's memories during a trial. Her presence induces intense fear and physiological reactions like vomiting in most individuals due to her miasma, though Subaru remains an exception while still perceiving her as profoundly dangerous. Her personality centers on an insatiable thirst for knowledge and obsessive curiosity, particularly towards unknown phenomena like Subaru's Return by Death ability. Superficially polite and amiable, she displays childlike clumsiness in daily tasks—such as accidentally setting forests ablaze or forgetting to change out of sleepwear—yet is fundamentally manipulative and sociopathic. Described as "black-hearted," she wields deceit and sophistry to satisfy her intellectual greed, showing little empathy. This extends to her interactions with Subaru, whom she initially offered a contract to exploit his ability before withdrawing support after his rejection. She harbors intense hostility toward Emilia, Satella (the Witch of Envy), and one other unnamed individual. Echidna's history spans over four centuries. She once advised royals across nations and co-founded Kararagi, later joining a group including Satella, Flugel, and Reid Astrea to "save the world." She tutored a young Roswaal L. Mathers, curing his mana poisoning and mentoring him until her death. Her creations include three artificial spirits—Puck, Beatrice, and an unnamed third—and she established the Sanctuary refuge for humans and demi-humans. There, she researched immortality via soul transference, creating clones of Ryuzu Meyer (Apostle of Greed) as experimental vessels. She died during the Great Calamity, purportedly killed by Satella, but preserved her soul and those of five other Witches within her Castle of Dreams in the Sanctuary. Following her physical demise, Echidna's soul oversaw trials in the Sanctuary to lift its barrier. In Arc 4, she manipulated Subaru by offering guidance in exchange for access to his Return by Death experiences. After he rejected her contract, she transferred her soul into the original Ryuzu Meyer's body, adopting the identity "Omega" and gaining the physical traits of a petite, white-haired child with pointed elf ears. As Omega, she travels with the other Witches' souls encased in a pyroxene crystal, observing the world without her former Authority. In Arc 6, she aids Subaru's group in the Pleiades Watchtower against threats like the Sin Archbishop of Gluttony, though her motives remain ambiguous. Her abilities are significant. Her Authority of Greed manifested as the near-omniscient Tome of Wisdom, granting access to past, present, and future knowledge. She mastered all six elemental magics, creating unique spells like *Al Shario* (summoning stardust) and unmatched teleportation—a skill rivaled only by Beatrice. She pioneered soul transference magic, requiring blood-related hosts for immortality, though Roswaal completed its development posthumously. Her creations include artificial spirits, Ryuzu clones formed from mana, and enchanted items like the Gospel books. After becoming Omega, she retains vast magical knowledge but loses the Tome of Wisdom, absorbed centuries later by Regulus Corneas. Echidna's relationships define key narrative arcs. She views Beatrice and the Ryuzu clones as "daughters," though she treats them as experimental tools. Roswaal remains devoted to reviving her, possessing descendants' bodies for centuries out of love. Her animosity toward Satella and Emilia drives covert antagonism, while her fascination with Subaru underscores her utilitarian disregard for emotional bonds.