When otaku and off-duty JSDF officer Youji Itami heads to a doujin convention in Tokyo's Ginza district, a colossal gate-shaped portal materializes out of nowhere. Out spill otherworldly beings and medieval warriors wreaking havoc in the city. Youji leaps into action, rescuing civilians as the JSDF combats the invaders. Months later, tasked with leading a recon team beyond the gate into the newly-dubbed 'Special Region,' he aims to forge alliances with the natives and unravel the mysteries of this uncharted land. Success means peace, but failure spells a catastrophic clash between worlds.