|This article is about the crystal used by Nephrite, Zoisite, and Endymion. For the power source of the Black Moon Clan, see Evil Black Crystal.|
The Black Crystal was created by Nephrite. After announcing his intention to locate the Silver Crystal, which was officially Zoisite's mission, he created the Black Crystal as an aid to locating it. Upon its first use, the Crystal indicated that Naru Osaka had the Silver Crystal. Nephrite tried to convince her to give him the Silver Crystal, but it ultimately transpired that she did not have it, and Nephrite theorized that the Black Crystal had actually been reacting to Naru's love for him.
Meanwhile, Zoisite was furious at Nephrite's attempt to steal his mission, and was acutely aware of the danger that the Black Crystal posed. After discovering Nephrite's interest in Naru, he assigned three of his Youma, Grape, Suzuran, and Housenka, to kidnap Naru and hold her to ransom for the Black Crystal. The Youma successfully kidnapped her, but Nephrite discovered their hideout and rescued Naru with relative ease. The Youma gave chase, however, and mortally injured Nephrite as he returned Naru to her home. Although Sailor Moon, Sailor Mercury, and Sailor Mars managed to destroy the three Youma, Nephrite died and Zoisite was able to steal the Black Crystal.
Shortly after the Black Crystal came into Zoisite's possession, Queen Beryl succeeded in partially awakening Queen Metalia, and was ordered to locate the seven Rainbow Crystals. Beryl then modified the Black Crystal to react to Rainbow Crystal holders and returned it to Zoisite, instructing him to find and remove the Rainbow Crystals. The Black Crystal was now able to not only locate Rainbow Crystals, but also to fire a beam of energy that would extract them from their host, leaving the host to revert into one of the Seven Great Youma. Zoisite used the Crystal to remove all seven Rainbow Crystals, although three of them were taken by either Tuxedo Mask or Sailor Moon.
After all of the Rainbow Crystals had been removed, Zoisite faced the prospect of taking back the three remaining Rainbow Crystals from Sailor Moon and Tuxedo Mask. To this end, he further modified the Black Crystal, granting it the power to transform any human into a Youma. He intended to use this power to turn Naru into a Youma, but the energy beam missed her and instead hit an actor portraying the sentai hero Redman. The actor was transformed into the Youma Akan, who then wreaked havoc for a short while in the Dreamland theme park.
Some time after those events, the brainwashed Prince Endymion proposed a plan to bring the seven former Rainbow Crystal holders together, uniting them to create an immensely powerful Youma. He used the Black Crystal to imprison his inhabitants, and succeeded in capturing Crane Game Joe, the priest from Yokohama, Yumemi Yumeno, Reika Nishimura, Rhett Butler, and eventually Ryo Urawa. However, before he was able to capture Rei's Grandfather, Sailor Mercury took the crystal and destroyed it, releasing the trapped inhabitants.