Listed below will be the different types of Keys used to summon Celestial Spirits.
~ Diamond Keys - Diamond Keys are unparalleled in strength, and the strongest of all the Keys in existence. Rumors exist of there being one for even the Celestial Spirit King himself. It's not known how many exist, but they seemed to be based on a single star in a constellation, and not the constellation itself. (Celestial Spirit characters can be made to embody these keys, but don't make it for your own character.)
~ Platinum Keys - Platinum Keys come in a set of twelve, each one based on the Twelve Chinese Zodiac. They are equal in strength to the Gold Keys, even though they differ very much. Much like the Gold Keys, only twelve exist in the world (and no, there's no secret thirteenth key... I think).
~ Gold Keys - Gold Keys also come in a set of twelve, based off the Twelve Zodiac Constellations. They are equal in strength to the Platinum Keys, though they differ quite a bit. There are only twelve Keys in the world, not counting Ophiuchus, which is considered a different colored key.
~ Black Keys - Apparently only two exist in the world, and are the secret "Thirteenth Keys" for both Zodiac based Keys. Though neither have them have been found recently, so it's only a baseless rumor. For now, at least...
~ Jade Keys - Jade Keys are only five of a kind, each one based on the "Four Symbols" of the Chinese Constellations. The Azure Dragon, the Vermillion Bird, the White Tiger, and the Black Tortoise. And then the once in the center of the four, the Yellow Dragon. These Keys are rumored to be more powerful than the Zodiac Keys, but given they're an incredibly rare find, none know for sure.
~ Silver Keys - Silver Keys come far and wide, each one being based on one of the 88 Modern Constellations. They are weaker than Gold, Platinum, Jade, and Black Keys in power, but are much more powerful than the Bronze Keys. All these keys are one of a kind, except for Nikorai's, who has an unlimited number of Keys.
~ Bronze Keys - Bronze Keys are just a random assortment of Celestial Spirits, of which are not based on any sorts of constellations. They are considered the weakest of their kind, and multiple versions of each Key exist for them all. They are truly unlimited.
