In the summer of 20XX, a mysterious gate opens in Tokyo's Ginza district, and a hostile army of soldiers and monsters pours through, turning the crowded shopping district into a warzone. Youji Itami, an off-duty, otaku member of Japan's Self-Defense Force, leads thousands of trapped shoppers into the Imperial Palace grounds and takes charge of the panicking police, an act that earns him the nickname 'Hero of Nijubashi.' This prequel manga traces the Ginza incident that leads directly into the original Gate story.