Demonic Fall Era

After tens of thousands of years of development, the world of magic and martial arts has reached its peak, but due to various disasters, it has been as difficult as a boat in the ocean. In an instant, the entire world fell into ashes. In this case, they suddenly discovered a new unexplored world of low magic, and the story unfolded from there. Are they an invasion? Or merge with each other? Don't guess. It's not the case anyway.