So... how exactly they thing she being the "lady of the holy sword" means they can act rude in front of the guy that can "make vulcanoes erupt just by being angry"?
She is immune to his magic but not to physical attacks which would be easily done by using magic to impale her with somthing or dropping lava on her, for example, and the other two are not immune to the magic meaning he can slice them without even moving piece by piece while making them unable to move.
Yes, I know the Demon King is not that vicious but it is still stupid of Cedric and Lilian to confront Claude like that.