When he discovered that what he had done would have a negative impact on the world, and when he discovered that he was no longer a hero but a scum in others' words, it was already too late.
He has become so obsessed with practicing martial arts that he slaughtered all his disciples for a copy of "Excalibur Style", and the smell of blood and gunpowder smoke dispersed in the wind.
So he stopped, and chose to watch the last child of that section being sent away, even though he knew that the "Excalibur Style" he wanted was in that child.
He expected this child to grow up and become stronger than him, and finally understood his sinful life with a sword full of hatred and resentment.
In the end, the hero is praised in the world for defeating the vicious villain, just as he longed to do as a child, even though his role in the story is that of a villain rather than a hero.
"This world needs darkness to show how dazzling the light of day is. This world needs evil to highlight the touching power of justice."