From the back of the book:
The temptation of the demon lords lure the wizards into darkness
"Demon lord seal" and "seal bearers"
"Demon Lord" is a supplement (collection of additional rules and data) for "Night Wizard The 3rd Edition", introducing the demon lords of the Rikai who are opponents of the wizards. In this book, the new rule '"demon lord seal" and "seal bearers"' is added as a new relationship between demon lords and wizards. The demon lords pushes their coat of arms called "demon lord seal" onto all their belongings to make them "seal bearers". Having received the seal, "seal bearers" are granted the power of the demon lord at the price of their soul. Can you resist the temptation of darkness?
Besides the "demon lord seals", we have prepared additional data to strengthen existing characters and classes and to widen special skills, brooms and their options. And in addition as new powers for recorders, we added 3 records, beginning with WW2 (air).