I will rebuild Japan in a world after nuclear war.

Decades into the future from present-day Japan, the world collapsed due to nuclear war. A thousand years after that nuclear war, in the year 3085 AD—or the 805th year of the New World Calendar in this world's reckoning—the world had regressed to a medieval age. In such a world, Japan had almost no human population. This was because China had fired all of its nuclear weapons at Japan. As a result, most of the Japanese people had been wiped out. However, in their place, there were many droids and androids, and until the true Japanese government returned, the nation was managed by the emergency national AI "Japan," which took control of the government during the former Japanese government's national emergency declaration, and by the surviving Japanese people. And then, a thousand years later, an event occurred that would change Japan.