In 2071, roughly fifty years after an accident with a hyperspace gateway made the Earth almost uninhabitable, humanity has colonized most of the rocky planets and moons of the Solar System. Amid a rising crime rate, the Inter Solar System Police (ISSP) set up a legalized contract system, in which registered bounty hunters, also referred to as "Cowboys", chase criminals and bring them in alive in return for a reward.
Kintaro Oe is a 25-year-old boy who left Tokyo University and now lives a simple life, traveling by bicycle to learn everything he can about the world.
After receiving a package from his grandfather, Ray, a young inventor who lives in England during the mid-19th century, finds himself caught in the middle of a deadly conflict related to a revolutionary advance in steam power.
