751 Book(s) Related to mushoku tensei anime end in light novel

Oscar Rivière, the heir of the Duchy of Rivière, learned he is bound to be married to the Duchess of Wingfall the very same day his father has arranged his departure. Strange rumors are told about his fiancée: a crazy noblewoman who eats men and feasts on the blood of innocents? Whatever is about to come, Oscar can only count on himself to discover the truth.