In 2019, on the cusp of a new era in Japan, a dimensional rift unexpectedly materializes in the sky, revealing a parallel world named "Shinkoku Nippon" where everything is inverted, with the sky and earth flipped. Maintaining their traditional militaristic ways, "Shinkoku Nippon" is forever stuck in the Eternal Showa era. The Japanese military launches a brutal invasion on Japan with the aid of imposing humanoid robots known as "Garann" and their potent gas weapons titled "Genmu," rendering Japan's contemporary weaponry optionless. As a direct result, "Shinkoku Nippon" hastily gains control of the government and triumphs over Japan. Accordingly, Japan's new era, "Reiwa," has now surfaced.