The subject of this article has not yet been localised outside of Japan by Konami. Please remember that these romanisations are non-canon.
Refiant were individuals created, or more accurately, recreated through the power of magic in order to become stronger and able to wield powerful magic. It was apparently not an uncommon procedure done before the destruction of the Old World. attracting many volunteers, but had since become a lost technique.
While the body of a Refiant would be able to wield more powerful magic than their original form and have a greatly extended lifespan, their lives would also be drastically shortened by continued use of their enhanced magical abilities. When the Terrus Firma attacked, many Refiants, old and new, would bravely fight the monster despite the obvious dangers, both immediate and to their lifespan even if they were to survive.
In the end, most of them would fall in battle. Lethe would consider herself the last of the Refiants some 100 years after the original battle against the Terrus Firma. However, the secluded Holy Emperor Renefarious would also be proven to be a Refiant, his lifespan extended indefinitely from his proximity to the True Era Tree.