A hero is made through sacrifice. With enough sacrifice, the gods will bestow that person with heroic powers to save the world or lead it. But of course it isn't free, it comes with a price. It always does. If someone becomes a hero, they are given a task they must complete, there's different kinds of tasks given to a hero- from helping out a tiny village overcome winter, to raising a country from the ashes, and the rarest of all tasks… it is to slay someone or something.
There are varying degrees of the slay task, it might just be slaying a certain beast that might kill a future leader or slaying an entire horde of monsters to slaying tyrannical leaders and unjust and corrupt people. The slay task is only given to a hero when something needs to be killed that threatens the future of this world, at least that's what the church said on how the gods decide to give the slay task.
Normally, the slay task isn't that hard, nobody in the world is stronger than a hero, blessed by the gods, a hero is a divine warrior that is here to do good. Which is also why there hasn't been a case in our world's 300,000 years of recorded history where a hero becomes a villain. The people who are given the heroic blessing are naturally heroic after all.
However there are some cases, two cases to be exact, where a hero failed and barely accomplished their tasks. It was to slay a demon. Demons are very rare to come across, in our history of mankind, only two have ever appeared. The first one appeared about 200,000 years ago and wreaked havoc in the far eastern side of the continent.
The demon destroyed and killed everything in its path, and according to history books, it was the first time something else overpowered a hero. The hero of that time was instead, slayed. And the demon continued on its path of destruction but eventually stopped. And now the far eastern lands are known to be the wastelands.
A place where no plants can grow and no living being can survive except for beasts. The mana there is so thick and corrupted that it will kill a normal person instantly. It has become an unlivable place, and a testament to the power and terror of a demon.
The second one appeared just a few centuries ago, however it was successfully slain by that generation's hero. Though it came with a price. The hero was apparently badly wounded in their fight and died alongside the demon. But well, the demon was still quelled so there's that.
As for me, I'm this generation's hero and an adventurer and my task is… to slay.