Unsouya no Ossan ga Nazeka Fukugyou de Zettai Muteki Kenshi wo Tsutomeru Koto ni: Saenai Jinsei wo Okutteta Ore ga Maou Toubatsu no Kirifuda ni?

The manga centers on Jack, a middle-aged freight company employee, who suddenly becomes the key to defeating the demon king, when he is told that he is blessed with the strength of a legendary swordsman. He then decides to become an invincible swordsman as a side job.

(Source: Anime News Network)