Zirconia serves as the primary ringmaster and field commander of the Dead Moon Circus, enacting commands directly for Queen Nehelenia, who remains confined within a mirror. Her name originates from zirconium dioxide, a diamond simulant gemstone. Communicating with Nehelenia through reflective surfaces, Zirconia relays the queen's orders to subordinates like the Amazoness Quartet and Amazon Trio. She oversees operations from her throne inside the circus tent, harnessing nightmare energy harvested from civilians to advance Nehelenia's goals of conquest and seizing the Silver Crystal. Her opening move unleashes a dark barrier around Tokyo during a solar eclipse, preventing Chibiusa's return to the 30th century and enabling the Dead Moon Circus's incursion. Zirconia orchestrates assaults against the Sailor Guardians, directing the Amazoness Quartet to deploy the Amazon Trio against Sailors Mercury, Mars, and Jupiter, trapping them within personalized nightmares that exploit their insecurities. Following the Trio's defeat, she commands Xenotime and Zeolite to target Sailor Venus. Zirconia intervenes personally, using an Amazon Stone to swap the ages of Usagi and Chibiusa in an effort to emotionally destabilize them. After accumulating sufficient nightmare energy, Zirconia plunges Earth into darkness by positioning a colossal black moon over the sun. She conjures a suffocating dark fog to incapacitate the Sailor Guardians and Tuxedo Mask, though purifying crystals dispatched from Elysion counter this assault. As the Amazoness Quartet begins resisting Nehelenia's corruption, Zirconia imprisons them within orbs and traps Sailors Chibi Moon and Saturn inside glass shards, delivering all six captives to Nehelenia through the mirror. During the final confrontation, the combined Sailor Planet Power Meditation attack from the Sailor Guardians weakens Zirconia. She retreats into Nehelenia's mirror realm with Sailor Moon in pursuit. After Sailor Moon liberates the captured Guardians, the mirror shatters from outside, causing Nehelenia's demise. Zirconia remains within the crumbling mirror realm, proclaiming Nehelenia's eternal reign before presumably perishing alongside her queen.