The Calamity of Killing Monsters

In ancient times, ancient demons from outside the world came, and the ancient demons preyed on humans. The human world was like a prison, and countless humans were kept in captivity just for food. At the time of the destruction of the race, a human ancestor stood up first, brought the four divine beasts and the human ancestors who dared to resist, seriously injured the demon king at the cost of his own demise, and sealed the ancient demon. Since then, the interface has been divided into two, and the ancient demon clan has been driven to another world. So far, the two worlds have been separated... As time goes by, the seal becomes unstable, the ancient demon resurrects, and the ancestors pass away. Where should the modern human race go...