There is a "border" separating the two realms of humans and monsters. However, after the war in the late Qing Dynasty, the barrier loosened. Some evil demons sneaked into the world to do evil, while some good demons hid in the market to survive.
◦ Xuanmen (the camp of demon catchers) is divided into two factions: the "Demon Slayer Sect" (which advocates killing all demons, which Shen Yan belongs to in the early stage), and the "Demon Crossing Sect" (which advocates distinguishing between good and evil, and later guides Shen Yan to transform).
