In the early 16th century, the perfection of the steam engine brought human life completely into the industrial age. Although it still faced the threat of various sub-human monsters, the pace of human progress was so unstoppable. However, human research on electricity has not made any progress. In the mid-16th century, the negative impact of industrial capital society continued to expand. In order to research more, more complex, and more sophisticated devices, one country after another began to increase tax rates, degrade the system, and even re-legalize the slavery system. At the same time, due to the influence of industry, the more developed countries are, the more serious their air pollution problems are. Most countries have serious smog problems. As a result, later people called this era the "Steam Age". It was against this background that two subhuman monsters entered a human society filled with people who were obsessed with life and death, and started a series of transactions at the cost of their souls with the "victims" who were driven by desire and emotion. This is how the legend of two demons began.