Not only that, he could not escape from her grasp; he soon realizes, "My powers... it's disappearing."
Yes, the girl was absorbing his powers. She is repeating the things that he has done to the witches.
But it was not her will to do so, for she has lost her consciousness after that hounding scream. It was actually the witches' spirit that he previously sucked dry, and as he grew closer to death, he could see their ghost and all of them look super pissed at him.
"Stop! Stop this!" He yelled, struggled and even tried to hit her to break free.
But she remained unfazed like an empty shell.
Though her head bleeds, she feels no pain at all.
It's as if the crown on her head had taken control over her mind and the only instructions she received was to destroy the villain that caused her grief.
With every second passed, the once muscular king slowly turned into a weak and frail senior citizen.