Viluy is the third member of the Witches 5 in the Death Busters organization. Her civilian identity is Yui Bidou, a Mugen Academy student and Sailor Mercury's academic rival. She harvests human souls to sustain the Death Busters' dying homeworld. Viluy possesses exceptional intelligence and specializes in technological warfare, primarily utilizing nanobots. These nanobots siphon victims' souls through computer interfaces and can be weaponized to dismantle opponents at a molecular level. Her abilities include generating computerized containment barriers and personal energy shields inscribed with chemical formulas. Her primary offensive technique, Mosaic Buster, fires nanomachines from a wrist-mounted device. Following Mimete's elimination, Kaolinite assigns Viluy to oversee soul collection. Viluy lures Sailor Mercury into a laboratory trap, displaying a model of the Tau Nebula before revealing she knows Mercury's guardian identity. During their fight, Viluy deploys nanobots and containment fields to subdue Sailor Mercury, having analyzed and adapted to Mercury's attack patterns. Sailor Uranus and Sailor Neptune intervene; Uranus's Space Sword Blaster penetrates Viluy's defensive shield, destroying her. Kaolinite's dark magic later resurrects Viluy temporarily. During this reappearance, she isolates Sailor Mercury from the other guardians, exploiting Mercury's aspiration to become a physician for psychological manipulation. Viluy then collaborates with the resurrected Witches 5, combining their technological powers to trap Sailor Moon within an amplified energy barrier. This plan is foiled when Sailor Uranus breaches Mugen Academy's defenses, Sailor Neptune destroys the Witches 5 collective, and Sailor Pluto frees the inner guardians. Viluy's character design consistently features pale blue hair and a primary association with ice-based powers. She is Sailor Mercury's direct counterpart within the Witches 5 hierarchy and holds a Level 202 ranking, signifying her position as the third most powerful member. Her character is named after the mineral viluite.