The country in which Radiant Chain takes place is called Radia. It is a kingdom led by King Radia XV. It comprises a fairly large continent, as well as an archipelago to the north.
Magic is commonplace in Radia, as is religion. Hidden throughout Radia are various Xana Crystals, which are said to be linked directly to magic in some way. The Gyth seem to be after these crystals, which is why they are so obsessed with causing trouble in Radia to begin with.