Vana'diel Bestiary: Kindred Warrior  

The Kindred are a particular sect of demons who have signed a blood oath with the Shadow Lord, entrusting him with the power over their life and death. They are unmatched in their absolute loyalty and immense power, which surpasses even that of the Demon aristocracy.

Some/all of the information in this article has been culled from various FFXI guides, and translated by Elmer the Pointy.