A gate to another world appears in the middle of Tokyo’s Ginza District, and the citizens of Tokyo are attacked by cavalry, dragons, and demons. Itami, an otaku who was in the area to purchase his long-awaited doujinshi, becomes the accidental hero of the day and gets promoted to second lieutenant of the Self-Defense Force. Not long after, he’s sent on a mission through the gate into the other world with typical otaku-like expectations of what he’ll find there.