Now that he's been betrayed by the demon king, the monster realizes that he can't use his powers to kill him. He's scared to death. He tells the monster that his primordial spirit isn't strong enough to keep him in his current form. The only way he'll be able to keep his human form is if the monster gets stronger. The two of them decide that the only way they're going to make it out of the current situation is for the monster to regain his strength.