In the manga, Zoisite first appears as Jadeite is being reprimanded by Queen Beryl following a failed mission. He later appears after Nephrite's demise and his emotions overcome him as he shrieks out the name of the lost king in sorrow. Kunzite then makes his entrance counselling Zoisite and offering the advice to "use his head" more than the other two failed kings. His first mission was to locate the Ginzuishou and follows several leads through news reports and press releases. In the end Tuxedo Mask's involvement was revealed and nearly the whole population of Tokyo was out looking for the mythical Silver Crystal so Zoisite switched his tactics to gathering energy instead. He does this in a spectacular way by using the Tokyo Tower to drain the energy of everyone in the city who was in contact with the video waves emanating from the tower. Kunzite is almost always shown with Zoisite, but they are not in a relationship as in the anime. They strategize together and Zoisite expresses concern about his own abilities and of those of the Senshi. Zoisite eventually devises a scheme to steal energy using electronic means, specifically rental movies that brainwash and hypnotize their victims. The Senshi arrive on the scene to confront Zoisite who in turn defeats them with almost startling ease. He is about to kill Sailor Moon when a curious Crescent Boomerang, care of the newly-arrived Sailor Venus, quite literally cuts him to shreds.
In the anime, Zoisite appeared the same time Nephrite came to power. The former king would cajole and ridicule the latter, often citing Jadeite's failures and comparing the two men on an intellectual level. His abilities are centered around nature, using fire, ice, and sakura petals in battle. Other abilities include teleportation (with additional weight), telekinesis, illusionary disguise, limited clairvoyance and supernatural strength and speed. Zoisite was resentful that Nephrite was chosen to replace the fallen king, feeling that it was his right to pick up where Jadeite had failed. The rivalry escalated from there with Zoisite taking every possible opportunity to make Nephrite look foolish, often in sight of the Queen. Worried that Nephrite would achieve his goal of the Silver Crystal, Zoisite sought counsel with the fourth king, Kunzite, with whom he shared a more than passing affection. Kunzite advised his lover to keep an eye on Nephrite's progress and his newly developed Black Crystal. Zoisite watched first hand as the crystal led Nephrite to Naru and his dormant human emotions began to emerge, saving the girl time and time again from danger. Finally Zoisite sprung a trap and kidnapped the human girl and forced an exchange for her life: Naru for Nephrite's Black Crystal. Nephrite refused, rescued her and took her to a park. Soon after, one of Zoisite's three youma assassins dealt him a mortal wound, Nephrite dropped the Black Crystal and Zoisite snatched it up. Zoisite then teleported away, leaving Nephrite to die in Naru's arms. Completely unfazed Zoisite then took control of the search for the Ginzuishou. It was revealed that the Mystical Silver Crystal had been split into seven component parts known as the Nijizuishou, or Rainbow Crystals.
Competing against both the Senshi and Tuxedo Mask, Zoisite managed to collect five. To win the final two the king challenged Tuxedo Mask to a duel, circumstances of which led to the masked hero learning Sailor Moon's true identity and vice-versa. Using several underhanded tactics Zoisite secured the seven crystals and, in defiance of Queen Beryl's orders, attempted to kill Tuxedo Mask. Unfortunately for the third king the wound he dealt to Mamoru caused the long dormant memories of the Moon Princess to awaken within Usagi. The tears she shed over her fallen love caused the seven Rainbow Crystals to merge back together into the Silver Crystal. This caused her to transform into the Moon Princess, Serenity. Zoisite was powerless against the Princess and fled to the Dark Kingdom where instead of asylum he was met with Queen Beryl's wrath. Angered beyond belief at his attempt to murder Tuxedo Mask, Queen Beryl mortally wounded the king as punishment. Zoisite begged his love Kunzite to grant his final wish and allow him to die beautifully. He died in Kunzite's arms, surrounded by flowers and his beloved sakura petals.
In the English version, and in several other countries, Zoisite was changed into a woman, perhaps as a means of disguising both his relationship with Kunzite/Malachite and his penchant for using female disguises.