A Key Crest (要の紋?) is a work of dwarven technology designed for use with an Exsphere. When used correctly, the Key Crest inhibits the negative effects of the Exsphere. It is made of a special "Inhibitor Ore" which can only be processed by a dwarf. Usually, the Key Crest acts as a mount for the Exsphere, but an accessory made of Inhibitor Ore with the correct charm carved into it will suffice. An Exsphere acts as a parasite in its host, and can be life-threatening without a Key Crest. If an Exsphere without a Key Crest is removed, the host's mana deteriorates. Victims of this incident include Marble and Alicia Combatir.