Steam City is a place where the only fuel source is coal, and the only means to produce energy is the steam engine. As the only source of energy, the steam engine has been the focus of technological advancement to the point where it can be substituted for any other form of power in modern technology. These same advancements also have given rise to Megamatons, large steam-powered robots. With the air of Steam City thick with fog and white smoke, thieves and criminals flourish with Megamatons as a common tool in their nefarious plans. It is here that the reader and/or viewer finds Narutaki, a young detective fighting for the peace of the city.