Everyone is a demon, why are you covered in holy light?

Yang Gu travels through the world of demons.
It happened that the dynasty was falling apart, demons were rampant in troubled times, and evil things emerged in endlessly.
In this world, ordinary people are like lambs left to the slaughter, struggling to survive, and Eucalyptus poplar is no exception.
The reason is because everything in this world has been contaminated by filth.
Anyone who enters cultivation, no matter the gods or demons, will pay a huge price, which has caused the distortion and abnormality in this world.
Fortunately, he discovered that he had the ability to completely purify all filthy things, eliminating all costs.
Kung Fu, spells, elixirs, magic weapons, puppets...
And when he mastered a technique called "Lamp-Lighting Technique", he discovered that when a fire was lit, evil things would be frightened and demons would avoid it.
Then...a strange idea came to mind.
He resolutely embarked on a path of practice that was completely different from the weird painting style of this world.