Karel is a bloodthirsty Sacaen swordmaster who appears to be insane. He lives only to find challengers worthy of his blade and will kill said opponents in battle without remorse or hesitation. His feats — including fighting Bern's armies alone, slaying a wizard that could freeze blood in a person's veins, and killing a warrior said to be many time the size of a normal human — have earned him infamy across Elibe, as well as the title of "Sword Demon". He is Karla's older brother and eventually teaches Guy some swordplay (if they support), and discovers that he is unwilling to kill them.
Source from Wikipeida