In a world where humans and demonfolk live side-by-side, a dark lord threatens to subdue the remaining free kingdoms. Ophelia, a demoness, escapes with her life after taking the life of one of the Dark Lord's generals--more like she ate him, actually. She then summons a great hero from another world to help defeat the onslaught of the dark lord's cohorts. But she gets Ian Foss instead, some ordinary guy who got 'isekai'd' (sent into another world from Earth) after being hit by (yes, you guessed right) a truck.

As the two of them try to figure out where things went wrong and what to do next, a series of events forces the two of them to work together and rethink their goals. But they do agree that falling for each other would be a most awkward thing.