Ryoumin 0-nin Start no Henkyou Ryoushu-sama

The war is over, and hero Dias is finally rewarded with land of his own—only to discover it's a barren frontier with no people, no villages, and no sign of civilization. With nothing but endless grassland ahead of him, Dias sets out to build a domain from the ground up. But after meeting Alna, a mysterious girl with a blue horn, his lonely frontier is about to spring to life.

(Source: Crunchyroll)