Offer him a cup of Kool-aid.

From Create Your Own Story

"Before you defeat me, please accept my kool-aid."

He drinks it, and suddenly, his pure aura turns into kool-aid! You laugh and flick him off like a fly, him spinning into the exosphere.

Your work is rolling along smooth, and finally, you're Emperor of Earth. You rule the Earth until your so-called son impales you with a Light Sword. Then, he brings the world back to normal, and everything is pure once more.