Japan, 2019, just before the dawn of a new era. Suddenly, a slit to another dimension world appears in the sky. What can be found there is the alternative world "Shinkoku Nippon" withe the sky and the earth upside down. This parallel world keeps the former militarism, its era being Eternal Showa. They military invade the real Japan with giant humanoid robots called "Garann" and their gas weapons "Genmu" that can make our modern weapons ineffective. "Shinkoku Nippon" instantly seizes the government and achieves de facto conquest of Japan. The new era "Reiwa" does not arrive for Japan.