Off-duty Youji Itami, a JSDF officer and otaku, is traveling to Ginza, Tokyo to attend a doujin conference when a mysterious portal in the form of a huge gate appears. When otherworldly beings and warriors wearing medieval armor emerge from this gate, they charge through the city, destroying and slaughtering everything in their path. While the rest of the JSDF focuses on preventing the invasion, Youji takes quick action to save as many lives as he can.
Three months after the assault, Youji has been assigned to head a special recon team as part of a JSDF task force that will be sent to the area outside the gate, which is now known as the “Special Region.” To discover more about what they are up against and to make an effort to make friends with the people in order to forge amicable ties with the reigning empire, they must venture into this uncharted land. But if they fail, they risk taking part in a terrible war that will consume both sides of the gate.
