Breath of Fire: Goddess Keys

Warning: The following may contain spoilers (depending on how you define spoilers).

In the first Breath of Fire game, there are six Goddess Keys, which were used to trap the Goddess Myria/Tyr. At the start of the game, the Dark Dragons are in possession of the six keys, and are attempting to release the Goddess. Throughout the game, Ryu and his team members try to get them back. The bolded headings are the menu names.

E.Key

The Earth Key is liberated from Nanai, where it is being used to power the quake machine. More specifically, it seems that the Quake Control simply amplifies the natural effect of the Earth Key, rather than being powered by it.

The E.Key can be used in battle to create an earthquake attack, which does a standard 30 damage to every enemy on the field. The E.Key can be used as many times as one wishes.

KngKey

The King Key is received in Agua, after defeating the Guardian of the Key. It is used to operate the Stone Robot.

L.Key

The Light Key is first heard of in Auria, where it is rumoured to be locked in the safe. In Bleak, the party learn that the key has been taken from there. However, after claiming the Dark Key, they are able to find the Light Key, safe and sound, at the top of the tower which can be reached through Ross' safe.  The key can be used to change the world instantly from night to day.

D.Key

In Bleak, the party learn that the Dark Key is related to the Goddess.  After Karn joins the party, they are able to travel to the top of the Light and Dark Tower, and claim the key by defeating Cloud.  The key can be used to instantly change the world from day to night.

TmKey

In Tunlan, the party learn that the Time Key is Tunlan's treasure, and that the Dark Dragon's are trying to steal it.  They also learn that it can control time.

The Princess of Tunlan is enamoured with Zog, and has decided to give him the Time Key, believing that he will use it to give her eternal youth. After several events involving explosions and hair-pulling, the Time Key is stolen by Jade's minion, Cerl.

Cerl uses the Time Key to trap Carmen in time.  Eventually, she sees the error of her ways, and gives the Time Key to the party.  However, when she tries to use it, Princess Nina is sent back in time, and can be found in Tunlan with amnesia.

SkyKey

The Sky Key is located at the top of Spyre, near Spring.  It's used to stop the eternal winter in Spring.