Lumen Histoire is located in a secret underground room in Fairy Tail's original building. This secret is only known by Fairy Tail's Guild Master and is passed on to the new Master successively. Precht showed it to Makarov when he became Master. Years later, Makarov showed it to Gildarts Clive when he told him that he wanted him to be next Master of Fairy Tail. According to Ivan Dreyar, Lumen Histoire is Fairy Tail's darkness, while according to Mavis Vermilion, it is Fairy Tail's light.
Later, it is revealed that Lumen Histoire is in fact the body of Mavis Vermilion encased in a crystal. Makarov also calls it the "ultimate weapon" of Fairy Tail.