For most of the residents of Tachikawa city, life seems to be perfectly normal. That's how it seems, but the truth, known only by a tiny select handful, is that this is a city at war. Every day, as the citizens go about their business, they are under attack by alien criminals and mysterious organizations seeking to conquer, enslave and destroy. But to combat these threats, a covert council has secretly selected certain individuals to serve as protectors.