Not only the commander-in-chief but all the demons who shot the arrows were scared after hearing her response. They were very clear on the purpose why they needed to catch the Cerulean Princess, it was because of her spiritual power. But now, she was saying that because of a different poison used which was attacking her power, she will turn into a mortal. A mortal! The beings who dies and enters the reincarnation cycle to live another life and die once again. That's unacceptable.
Also, the Demon Lord promised the Emperor and the Queen that he won't kill their daughter as long as she handed her spiritual power to them. Yet, he can't even get the power and the princess will become a mortal. He lost two things and gained nothing.
