Easygoing Territory Defense by the Optimistic Lord: Production Magic Turns a Nameless Village into the Strongest Fortified City (Manga) Vol. 1

Van, the fourth son of a powerful noble, is only two years old when he remembers his past life as a salaryman in Japan. With his adult brain in a young body, he's considered a child prodigy... until he displays the 'Production Magic' skill when he turns eight. In a family that favours offensive magic, this crafting skill is considered useless in battle, and Van is banished to oversee a tiny country town in disgrace. With only his personal maid, the memories of his past life, and his 'worthless' magic, can Van improve the fortunes of this little village - and himself?