After killing Liu Meixiu, Wang Wei felt at peace. His state of mind did not suddenly undergo any changes, after all, he has gotten used to the fact that death is a normal thing in the world of cultivation.
You could say that he has become desensitized to death. And after understanding some power of fate, he knew that it was the fate of many mortals to die at the hands of cultivators.
Despite all of this, he was still a little bothered by what happened in the Qi Luck Trial. As such, he had long planned to kill Liu Meixiu, no matter what.
So, as he watched her body fall to the ground and her soul destroyed, he felt relieved, calm, or at peace.
Wang Wei sighed lightly. He raised his hand to burn her body, then, he suddenly remembered the Fiendgod 12 Revolution that he just received and an idea popped in his head.
So, he immediately sealed the pieces of her soul that were about to disappear and put the body away.