In 2431, the overuse of resources by humans caused the ozone layer that originally covered the Earth's surface to cease to exist. Ultraviolet light directly confronts vulnerable humans. As the original inhabitants of the earth, humans are forced to start the "autonomous evolution plan" in advance as a means of coping with future risks. The "Autonomous Evolution Project" is a project developed by elite scientists from all over the world. This project aims to change human genes to enhance human resistance to ultraviolet rays and high temperatures. Due to the large amount of work and the wrong estimation, the crisis came early. Even with the vast majority of the world's scientists, the project was not completed within the expected timeframe. The study was less than half complete. But by this time, the development of events had threatened the survival of humanity. After deliberation by the heads of state, it was decided to launch the No. 46 evolutionary ray from the satellite recklessly, and release the No. 46 evolutionary ray to the entire earth in a full-coverage manner, so as to complete the purpose of human independent evolution. As a semi-finished product, ray 46 is capable of altering the genetic structure of the human body. However, due to the fact that it is a half-finished product, the ray has a huge flaw. Not only are there individual differences in effectiveness, but there is also no way to know the possibility of other creatures existing. The possible consequences cannot be assumed. In order to avoid being affected by Ray 46, the magnates of the world who learned the truth of Ray 46 entered the underground shelter that had not yet been fully completed in advance, and at this time, the ordinary people who did not know the truth sighed at the power of science while receiving the baptism of Ray 46.

In 2440, the discovery of the first mutant creature of the Ironclad family in Kula Sahar, and a series of subsequent events accelerated the progress of the "Deep Sea Palace" project. When the Investigative Bureau of the Kura Sahar discovered the mutated ironclad creature, the insect with a diameter of less than 3 cm in the encyclopedia was already 3 meters in size, and it was already carrying three human lives. Although Ray 46 gave the "New Human" armor-like skin, this layer of skin was rendered useless in front of the under-mouthed creature, and the victims' bodies were shriveled like wringed towels, completely dehydrated, and even the bone marrow was eaten away.

In the past nine years, the world's total population has been declining, from 8 billion to 7 billion, a drop of one-eighth of the total population. But the rate of decline is growing. While news outlets around the world continue to report on the disappearance of people, the powerful people in the underworld are glad that they believe that moving to the underworld early is the right decision. While the construction of the underworld began to be accelerated around the world, the magnates seemed to have grown a moss-like disease on their arms due to the lack of sunlight in the underground for a long time, and there was no cure for it. Soon, however, this became a source of pride for the magnates, as the disease only appeared in the bodies of the magnates who had entered the underworld in advance. So this disease became a way for them to identify other powerful people. Aware of this, the magnates poured capital into scientific research, hoping to spread artificial sunlight to every corner of the underground world as soon as possible, in case the "inferior people" who came in later would also acquire the same characteristics.

In 2459, the darkest year since the implementation of the Human Autonomous Evolution Program, it is no surprise that the mutant ironclad family seems to be more friendly to other animals except mammals, especially reptiles, insects, and birds, in this world of natural selection. With the help of ray 46, these three types of creatures are evolving at an incredible rate, not only in size, but also in IQ.

In the winter of 2459, a catastrophe called the "Hundred Worms" struck Linsrig, and some of the circumstances can still be read in the relevant documents.

"It was winter, and there were no insects in a cold winter, but when I looked up, the whole sky was covered with flying insects, and if it weren't for the sound of the wings of these beasts, I would have thought that the black oppressive piece was the eye of the storm! What's even more terrifying is that these guys attacked the building, and ordinary guns didn't hurt the guys at all, and the whole city slowly turned into a ruin right under my nose...... Luckily, the surface convoy arrived, and although some people were killed, they drove away the crazy monsters. "This is a book called "Survivor's Notes", which contains a detailed account of the insects who played a role in this disaster. Termites, jawed ants and other creatures have wreaked havoc in a city that has been covered in snow all year round, and the great Linslig Memorial Square has not escaped its fate, and the surface guards have only driven it away, and these behemoths will continue to wave their wings and encroach on more surface cities.

By the time people realized that the catastrophe had arrived, the world's population had plummeted to less than 4 billion people. And who would have thought that in 2468, after the construction of the underworld and artificial sunlight, there were only less than 3 billion people left in the entire human race to the underworld.

The Surface Guardians were established at the beginning of 2459, and the space for human existence on the earth where xenomorphs are proliferating is constantly compressed, and the magnates who are aware of this also know that if they do not take action, the surface humans will ignore the rules and flood into the unfinished underground world. So the magnates finally took measures, demanding that all countries immediately form surface escorts to defend the living space of human beings on the surface, and of course, to defend the order and stability of the underground world from the interference of "untouchables".

The members of the surface guards of each country are human beings whose physical fitness has become extremely good after receiving Ray 46, and they are given extremely high rewards and full freedom in exchange for the loyalty of this group of highly capable people.

It's a pity that with the passage of time, there are fewer and fewer humans on the surface, and the members of the escort team have also transferred to the underground world one by one, until 2468 all the surviving humans have transferred to the underground world, and the human race has completely lost its sovereignty on the surface.

Humans unanimously believe that they will regain the dominance of the surface one day in the future, even after moving underground, there are still some human beings who will collect resources that belong to the surface, this group of people are called surface explorers, which sounds ridiculous, and the human beings who used to be the overlords of the surface actually formed a team called surface explorers, relying on these people to obtain surface resources.

In addition to the official surface explorers, other humans who want to go to the surface to collect resources are required to apply for a surface activity permit, and those who have a permit can take the surface tunnels built in various cities to the surface to carry out daily activities.

Life in the underworld in 2495 is no different from the surface world of the past, people have become accustomed to living underground, and under the artificial sun, many people no longer miss the feeling of being shrouded in ultraviolet rays, and the tunnels that rise to the surface from time to time in the center of the town are no longer the focus of attention. People no longer care who enters the tunnel and who comes out of it, and lives day in and day out.