Queller demon

According to Xander’s book, primitive people used to believe that the moon was a cause of insanity. Sometimes they would pray to the moon to send a special meteor to fix the problem the moon had caused. These meteors were expected to quell the madmen, which they did, due to the Queller Demon which arrived inside them. The Queller, which looks rather like a large cockroach with an ugly face, hunts out the insane and 'quells' them by vomiting slimy fluid into their mouth, causing death by suffocation.

Although the Queller Demon appears to be a fictional creation by the writers, interestingly, there is a legend of a Demon Queller. Supposedly in eight Century China a brilliant physician named Shoki was rejected by the Emperor because of his ugliness. Shoki committed suicide in shame, and the remorseful Emperor ordered him buried in great honor. In gratitude, Shoki’s spirit protected future Emperors from demons.