Gyakuten Sekai no Denchi Shoujo

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 "...