Easygoing Territory Defense by the Optimistic Lord: Production Magic Turns a Nameless Village into the Strongest Fortified City (Manga) Vol. 3

Van leads the villagers in battle against a horde of armored lizards, and thanks to his "useless" production magic, victory is theirs! But just when Van starts enjoying his new lifestyle, more threats emerge, including the local count and a horde of...merpeople?!