The Nightray Dukedom is one of the four noble houses. It has been clearly stated that they are the enemies, opposites, or rivals of the Vessalius Dukedom.
The Nightray house is considered "the Dark" due to the rumors of them being in cahoots with the Baskervilles 100 years ago, whereas the Vessalius house is considered "the light" due to being thought of as the heroes of 100 years ago. They also carry the Chain Raven. Not much else is known about this family. Currently, the family is now extinct with all real family members dead.