Fortune Builder: The Nation Levels Me Up

The invasion has to be stopped before it starts, and the world has already failed at that once. On 4 May 2760 the demon clan comes down on the planet, and inside a month one country after another has fallen. One of the people caught in that month opens his eyes on the day before it begins. A system opens for him and he wakes a class rated SSSS, National Fortune Builder. He takes it to his own government. National resources and manpower go into what the class lets him raise, the Great Wall, the Godslay Swords, and summons that ancient gods answer. Millions of people are behind the work by the time the counterattack on the demon clan begins.