A person with a monster mind means the person has the body of a normal living being but the mind of a monster. A mind that only seeks destruction like the monster itself, especially towards the civilian society.
This change could happen to every person. It is similar to a mental disorder. The cause of this phenomenon comes from many factors such as continuous mental abuse, physical torture for a long time, or getting overstressed by something for an extended time.
Although they have a monster mind, it doesn't mean their wisdom and intelligence are gone. This makes them more dangerous than ordinary monsters, who are like mindless beasts.
Usually, people will immediately kill the changed person before it could cause more damage. There are even stories about small countries getting destroyed by this changed person. Furthermore, there is no cure to reverse people with monster minds up to this day.
