Crystal (term)

Crystals are legendary elemental objects that have appeared in multiple games in the series. They are said to be the gems that control natural phenomena. There are usually four Crystals: a Water Crystal, a Fire Crystal, a Wind Crystal, and an Earth Crystal

Final Fantasy IV
There are eight Crystals in this game. The four elemental Crystals form the "Light Crystals," and are kept in the Overworld. The Crystal of Water is in Mysidia, the Crystal of Fire is in Damcyan, the Crystal of Air is in Fabul, and the Crystal of Earth is in Toroia. However, there are also four other "Dark Crystals" that are kept in the Underworld. The location of two of these Crystals is never revealed, but one is kept by the Dwarves in their castle, and one is found in the Sealed Cave. If all eight Crystals are gathered in the Tower of Bab-il, it has been told that the "way to The Moon" would open. However, gathering the Crystals there would actually summon the Giant of Bab-il, a wish granting giant. The Lunerian Zemus wanted to have the Giant destroy the Earth so that the Lunerians could settle there, and he used Golbez to do so.

There is another "Crystal" that appears in the battle with Zeromus, and it is an item that is said to make Zeromus tangible and defeatable. Golbez tries to use it on Zeromus, however, only those born out of the Light can use the Crystal. When Cecil Harvey used it, Zeromus became tangible, and Cecil and his friends defeated Zeromus.

Final Fantasy V
There are four Crystals in this game. They control the elements in the First World, and without them, the wind would not blow, the oceans would dry, the fire would burn out, and the life of the earth would be destroyed. The Wind Crystal was kept in the Wind Shrine which was maintained by Tycoon, the Water Crystal was kept in the Worse Tower and maintained by Worse, the Fire Crystal was kept in Karnak, and the Earth Crystal was located in the Ancient City. Long ago, the Warriors of Dawn used the power of the Crystals to seal Ex-Death within the Earth.

At the dawn of the adventure, a man named Cid Previa invented a machine with the power to amplify the output of the Crystals. However, if the Crystals were allowed to operate at this capacity, they would shatter. Cid deeply regretted creating the machine. At the same time, Ex-Death was trying to shatter the Crystals himself so he could become free. However, the Crystals all eventually shattered, and each shard became the source for a new Job Class for the characters.

In the Second World, the Crystals are replaced by the Seal Guardians who guard Mua Forest.

Final Fantasy IX
Although the Crystals do not appear in this game, there are four "jewels" which were being sought by Queen Brahne of Alexandria. Princess Garnet ran away with Alexandria's own jewel, and Lindblum, Cleyra, and Maidain Sari each owned a jewel. If all four jewels came together at Alexandria, the Eidolon Alexander would be summoned. Brahne eventually gathered all the jewels, however, she died shortly after. When Kuja attacked Alexandria using Bahamut, Garnet and Eiko Carol used the jewels to summon Alexander.

Another Crystal is said to be the source of life in the world, however, it is not seen until the very end of the game, in which Necron tries to destroy it.

Final Fantasy Mystic Quest
There are five Crystals in this game.

Super Mario RPG: Legend of the Seven Stars
The four Crystals make a cameo in this game as guardians of Culex.