This story follows Gift of the Mazouku.  Xelloss has absorbed the powers and position of his past mistress, Zelas, and is, as a result, a Demon Lord himself.  Valgaav has grown up to be young Val (Valentine) and is traveling, by choice, with Xelloss for training purposes.  Lina, Gourry, Amelia, and Zelgadiss have been reunited to explore a strange phenomenon.  Reading Gift of the Mazouku is not required to continue—understanding these points are sufficient.