Query: Who are the main characters in the spin-off books?
Context: The main characters in the spin-off books from the Night Huntress series vary depending on the series. In the Night Prince series, the main characters are Vlad and Leila. In the Night Huntress World series, the main characters include Spade and Mencheres. Each spin-off series introduces new and intriguing characters that add depth and complexity to the Night Huntress universe.