Filvis Challia served as captain of the Dionysus Familia in Orario. She presented as an elf with long black hair and red eyes, typically clad in a frilled white dress and a light blue-edged white coat. Her physiology transformed drastically upon becoming a Creature: her hair lengthened to touch the ground, her eyes darkened to blue and sunk in shadowy sockets, pale red root-like growths extended from the magic stone embedded in her chest, and her skin turned bluish-white. Like most elves, she avoided physical contact with others, including fellow elves, believing herself unclean; this aversion intensified after her transformation. She openly dismissed forming bonds outside her race. Her direct manner and lack of concern for others' impressions often appeared impolite. Yet, Filvis demonstrated profound loyalty to those she considered true friends, especially Lefiya Viridis of the Loki Familia. She personally taught Lefiya advanced techniques like concurrent chanting and the use of Dio Grail magic. Throughout the conflict orchestrated by Enyo, Filvis repeatedly broke from plans to shield Lefiya from danger. During the Nightmare of the 27th Floor, she sacrificed herself fighting a Corrupted Spirit to save her companions when escape remained possible.

Following her Creature transformation, Filvis developed intense devotion to the god Dionysus, who accepted her monstrous form. She followed his commands unconditionally, aware she was being used. The transformation and subsequent trauma caused severe mental instability. Horrified by her existence, she made multiple failed suicide attempts, deepening her despair. The persistent voice of the Corrupted Spirit further fractured her psyche, leading her to transfer her hatred and pain onto a magical duplicate named Ein. Ein harbored intense hatred towards the original Filvis, mocking her suffering, delighting in her misfortune, and scorning her self-pity while claiming to endure the true agony. Ein also displayed aggression towards others, accusing Revis of betrayal and labeling captured Evilus members as incompetent. Despite this hostility, Ein shared Filvis's affection for Lefiya, expressing regret they hadn't met before Dionysus and shedding a tear over Lefiya's fate.

As a Creature, Filvis possessed formidable abilities. Her strength, speed, agility, reflexes, durability, endurance, stamina, and mind were significantly enhanced, placing her whole physical prowess in the high Level 7 tier. She consumed magic stones to grow stronger, though her body required large quantities due to a high consumption rate. Her bugged falna still enhanced her base abilities. Her duplication magic, Einsel, split her status into two Level 3-tier entities. She demonstrated immense strength by easily stopping and crushing Bete Loga's fist, generating shockwaves capable of severely injuring Lefiya. Her speed allowed her to move like a whirlwind, wiping out dozens of adventurers before Lefiya could react. She deflected Lefiya's Arcs Ray and withstood attacks from a pseudo-Level 7 Bete using Hati, along with explosions from Fusillade Fallarica. She exhibited inhuman pain tolerance, fighting on despite severe injuries. Her accelerated healing consumed stamina and mind to regenerate wounds, slowing when reserves depleted. Roots growing from her magic stone moved instinctively to protect it. Filvis was an expert magic swordswoman, skilled in concurrent chanting and versatile in close and ranged combat. Six years of using Einsel granted combat experience nearly equivalent to a first-class adventurer. Her senses, particularly eyesight, were exceptionally sharp.

Her magical abilities included Dio Thyrsos, generating blasts of golden lightning (turning black and more powerful in her complete form), and Dio Grail, which created circular white barriers; both were super short chant magics. Einsel, her duplication magic, halved her status while active. Known skills included Fairy Senior, Monstrum Union, and Darklight. Her Mage development ability boosted her magic power equivalent to one level above her other stats, granting Level 4-tier magic to each half and Level 8-tier magic when whole, while improving range, efficiency, and manifesting magic circles (white for halves, black when complete). Her equipment included Tear Pain, a mind-enhancing short sword forged from materials from her home forest of Ashenia, and Guardian's White Torch, a wand crafted from a Holy Tree of another Elven forest, given after she obtained Dio Grail.

Her involvement in Enyo's plot unveiled her double life as Ein. She infiltrated the Loki Familia's efforts to investigate Knossos and the Demi Spirits under Dionysus's (Enyo's) orders. During the final confrontation, her true identity was exposed to Lefiya. After Dionysus's defeat and subsequent suicide, Filvis expressed remorse before dying in Lefiya's arms. Her actions throughout the conflict, manipulating events from within the alliance against Enyo, were driven by loyalty to Dionysus and a desire to protect Lefiya, culminating in her death during the battle to save Orario.