Lord El-Melloi II-sei no Jikenbo (Novel)

Ten years after the Fourth Holy Grail War, Waver Velvet, now Lord El-Melloi II and in charge of the Department of Modern Magecraft, solves problems and investigates mysteries in the thaumaturgy world on behalf of magi with the help of his apprentice Gray, all the while navigating the cutthroat politics of the Clock Tower.