Black Crystal

Belonging entirely to the debut season of the 1990s anime, the Black Crystal is a crystallized tool wielded by the Dark Kingdom and never to be mistaken for the separate Evil Black Crystal. Nephrite first created it after giving up his Celestial Map, hoping the new object would lead him to the Legendary Silver Crystal and restore his standing. Across the season it moved through the hands of three different Shitennou plus the brainwashed Endymion, and its role shifted with each owner. Sailor Mercury finally put an end to it in the forty-first episode.

The gem began as a scrying device, glowing and projecting illusions in response to powerful energy. In Nephrite's hands it lit up with the image of Naru, misleading him into thinking she carried the Silver Crystal when it was really reacting to the strength of her feelings for him. Queen Beryl later retuned it so that it answered specifically to the seven Rainbow Crystals, allowing it to find and draw those shards out of the reincarnated Youma who unknowingly carried them. Immersed in a cauldron of potion, it gained yet another power, converting ordinary people into Youma. In its final role it was meant to imprison the former Rainbow Crystal carriers and fuse them back into a single overwhelming monster.

Nephrite made the crystal and used it first, only to be ambushed and killed by Zoisite, who stole it for himself. Under Beryl's modifications Zoisite then tracked down the Rainbow Crystal holders and later tried to weaponize the gem against Naru, accidentally transforming an actor into the Youma Akan instead. The brainwashed Prince Endymion took up the crystal last, attempting to trap the healed carriers within it, before Sailor Mercury wrenched it away and dashed it against the ground, shattering it and setting the captives free. Jadeite alone among the four generals never handled the item, and whether Kunzite ever employed its monster-making power was never shown on screen.