Mysterious Beings (怪人, Kaijin) or Monsters are terms used to refer to sentient creatures that terrorize the cities of the entire planet and pose a threat to society. They have been appearing more frequently in the past 15 years, but humanity still is unaware how most of these creatures came into existence. It is still unknown what their actual purpose is, but it seems that most of these creatures are hostile towards mankind, wreak havoc in the cities and terrorize its citizens.