The Darkfever Plague was a magical disease that was unleashed upon the lands of the Phoenix Clan in 1123 after a Solar Eclipse freed Kuzushi no Oni from its prison. The plague was lethal, spread with magic from the oni's prison in a forgotten estate deep within the Isawa Woodlands. It poisoned the elements in parts of the Phoenix lands, and caused those who drew on the power of the elements there to become corrupted. The disease killed many people until the oni was destroyed.