Unsouya no Ossan ga Naze ka Fukugyou de Zettai Muteki Kenshi wo Tsutomeru koto ni: Saenai Jinsei wo Okutetta 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)