He'll beat them so bad the demons will have to declare war out of fear... But really though, that peace sounds fragile as shit.
A plot that relies on characters in the know being vague for unexplained reasons is frustrating and I've never seen one where it was justified, oh well.
I suspect in the end, the Guildmaster will probably go something like "Oh, that?", and nonchalantly spill the beans. Probably say he could've just asked, and everyone will freak out and scold him for not listening to other people.