Seven Rainbow Crystals

These seven stones are what remains when the Silver Crystal breaks apart, and locked inside each one is a member of the Seven Great Monsters, the Dark Kingdom's fiercest fighters. Long ago Queen Serenity of the Moon Kingdom shaped them into prisons for those enemies. Every shard takes on a separate hue drawn from the classic seven bands of the rainbow, which is where their name comes from.

Over time the crystals end up buried within the reborn monsters, who now walk the Earth as ordinary people carrying no memory of their former lives. Zoisite and Kunzite eventually gather the whole set and rouse the monsters again, only for Sailor Moon to cleanse them and reclaim the mended Silver Crystal. The Rainbow Crystals belong solely to the opening season of the 1990s series.

Sealing a monster inside a shard neutralizes it, since none of them can spread their evil while trapped. Pull the crystal out of its host, though, and that person snaps back into monstrous shape. The gems ride to Earth alongside Princess Serenity and her guardians, and the Great Monsters are reborn within regular humans, with one exception being a cat. The hosts stay unaware of what they carry, yet in some the buried power leaks out as gifts like telekinesis or other mind-based talents.

The reunited whole is the point of it all. When the Dark Kingdom finally holds every shard and Tuxedo Mask is hurt trying to take them back, Sailor Moon's grief makes the seven align to her. They fuse with the tear she sheds, and the Silver Crystal takes form once more.

Queen Serenity first bound the monsters into the crystals during the age of the Moon Kingdom. Generations later Queen Beryl orders Zoisite to track the shards down so the Silver Crystal can be rebuilt and Queen Metalia fully revived, handing him the Black Crystal to sniff out and pry loose each gem. The hunt sprawls across several episodes, with the Sailor Guardians repeatedly clashing with the freed monsters; rather than kill them, Sailor Moon uses Moon Healing Escalation to lock each one back inside its host.

The seven hosts span a red shard in Crane Game Joe, orange in a Priest, yellow in Ryo Urawa, green in Yumemi Yumeno, blue in Reika Nishimura, indigo in Rei's grandfather, and violet in Rhett Butler, the lone non-human carrier. Zoisite, Kunzite, and Tuxedo Mask all seize shards along the way before every fragment merges with Sailor Moon's tear.