The game is set far into the future of the Crystal Chronicles franchise, taking place in the same world as Final Fantasy Crystal Chronicles, populated by four races. However, due to a war with the Lilty race, the Yuke race has supposedly died out, though that clearly isn't the full story. The setting has been recently described as a time when "swords have changed to guns" and the arcane arts are outlawed by the Liltian Kingdom. However, magic reappeared in to the world in the form of people born with the power of magic inside of them, these people were named by others as "Crystal Bearers" for a common trait crystal bearers had of being born with a random crystallized body part like an eye or a small section of the skin. In March 2008, an official advertising article about Final Fantasy Crystal Chronicles: Ring of Fates noted that the Nintendo DS installment "sets the stage" for The Crystal Bearers.
Source: Wikipedia, "Final_Fantasy_Crystal_Chronicles:_The_Crystal_Bearers," available under the CC-BY-SA License.