The setting of Radiant is an universe where individuals reside on separate islands high above the skies. One day, terrifying creatures known as Nemesis suddenly arrive out of nowhere and wreck havoc on the planet. They infect anybody they come in contact with. However, a few individuals have lived through the often fatal encounter with the Nemesis. The only people who can currently engage the Nemesis in combat are the infected, who have been given extraordinary abilities. The Infected are dreaded by the remaining humans, despite the perilous encounters with the Nemesis.
Seth, a young orphan and aspiring magician from the Pompo Hills, is one of the infected. His everyday activities include locating and combating the Nemesis with the aid of his master Alma. Seth understands that he must track down the Nemesis's origin in order to completely defeat it. Seth decides to investigate the so-called Radiant, the origin of Nemesis, on his own. He is joined by other wizards, and the two of them scour the globe for an object about which no one is certain of the whereabouts while being watched over by the Inquisition.
