Petz, sometimes romanized as Petzai, is the eldest of the four Ayakashi Sisters, also known as the Specter Sisters, a quartet of female operatives in the Black Moon Clan during the second story arc of the anime. She is named after the mineral petzite and serves as a dark counterpart to Makoto Kino, Sailor Jupiter, sharing that character's association with electricity and storm-based power. She is portrayed as a mature young woman with green hair worn in an updo, black feather ornamentation, and a dress paired with dark tights.

Before she gained her abilities, Petz was an ordinary person whose powers were awakened by the energies of Planet Nemesis. Along with her sisters, she came to serve under the clan commander Crimson Rubeus, supporting the Black Moon Clan's efforts to overthrow the government of Crystal Tokyo in the future. In her role as an operative, she is deployed to Earth to carry out the clan's schemes and do battle with the Sailor Guardians.

Petz is notably proud and ambitious, willing to step on others in order to achieve personal glory and power. She frequently clashes with her sister Calaveras, although most of their missions ultimately end with the two working together. She also carries bitterness over a failed romantic relationship from her past and reacts sharply whenever Calaveras teases her about it. Her loyalty to Rubeus is genuine, though Rubeus ultimately regards her and her sisters as expendable tools.

Her most significant relationship is with Saphir, a high-ranking member of the Black Moon Clan. Petz and Saphir were romantically involved in the past, and that relationship is the source of her later resentment toward men. When she and her sisters later discover a wounded Saphir, she tends to him even though she initially suspects he has come to punish them. After Saphir is killed by Wiseman, Petz senses his death and is heartbroken, though she takes comfort in remembering how he once smiled at her. Her bonds with her sisters are also central to her story; despite her friction with Calaveras, the sisters ultimately save her life, and she is purified alongside Calaveras at the conclusion of the arc.

Petz undergoes significant development over the course of the story. After two of her sisters, Cooan and Berthier, defect from the clan, Rubeus entrusts her with a staff said to infinitely increase her dark powers and orders her to eliminate both the Sailor Guardians and her fallen sisters. The staff greatly amplifies her strength, but it also corrupts her personality, driving her to turn on Calaveras and attempt to kill her as well. When the Guardians manage to knock the staff away, Rubeus reveals that he had expected Petz to fail all along; his real scheme was to use the four sisters as bait to lure out the Guardians and sacrifice them all. He then activates the staff's true power, which creates a massive time-vacuum threatening to consume everyone nearby. Freed from the staff's corrupting influence and filled with remorse, Petz resolves to throw herself into the vortex to destroy it, but her sisters stop her. The Sailor Guardians succeed in destroying the vortex, after which Petz is purified along with Calaveras.

In battle, Petz's signature ability in the anime is Dark Thunder, a dark lightning attack that reflects her connection to Sailor Jupiter's thunder-based powers. She is also capable of using other dark-energy attacks, and her abilities become dramatically more powerful while she is under the influence of the staff given to her by Rubeus.