What If It Could Keep Evolving?

In the year 2899 of the Old Era, the Fifth World War began, and 60% of the earth's population disappeared. The war started because of the invasion of alien species. The alien species have extremely strong evolutionary capabilities and can even disguise themselves as humans. The earth had to establish a "sky system" to resist alien species, but this also limited the development of human beings. The United General Agent issued a statement that mankind will take 500 years to eliminate all remaining alien species on the earth, and another 500 years to improve technology and officially declare war on the alien species! This novel and its characters are purely fictitious. Any similarity is purely coincidental and should not be imitated.