Briefly about Ossan, Yuusha to Maou wo Hirou manga:
An old man is forced to retire from the adventurer’s guild and decides to return to his hometown.
On his way, he picks up two babies. The first one is a human baby with the emblem of a hero.
The second was a baby of the demon tribe with the emblem of the demon king.
And so the story of the old man who picked up the hero and the demon king begins.