Ossan, Yuusha to Maou wo Hirou

Story:

The main character retires from the Adventurer's Guild and decides to return to his hometown. On the way, he falls into an adventure and takes two babies with him. The first infant is a human infant with the emblem of a hero. The second was a baby from the tribe of demons, had the emblem of the demon king. This is how the story of the old man begins, who raised the hero and the demon king in his arms.