Fate Stay Night story mix with Manhwa Hero has Returned.
Shirou had always wish to be a hero, but he never thought he will be summoned into another world to beat the Demon King. However, being the good guy he is he went and accept the request and finally defeat the Demon King. After defeating the Demon King, Shirou decided to return to his old world to avoid himself being used as a weapon by the human who are greedy for further power.
Returned to his old world he expect to become a mercenary in the hope to be the hero this time in his own world. However, what comes to his sight is a world where people who summoned like him use their power to conquer the world.