Demon King, Hero and King

In order to break the dark magic of the devil and eliminate monsters, the king has been sending "king missions" to the devil for fifty years to eliminate the devil... But in the end, no one survived in the more than twenty king missions, and the tax law was also increased with the dispatch of the king mission... But the king mission in front of him succeeded, they defeated the devil... Did they defeat the devil... (Originally, there was a classmate in the class who was writing a novel, but I thought his writing was too good, so I said I would write a better novel than him XD)