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.

这是一个关于你自身的故事。你体内的故事——。 人的细胞数量，约为37兆2千亿个。 细胞们在名为身体的世界中，今天也精神满满、无休无眠地在工作着。 运送着氧气的红细胞，与细菌战斗的白细胞……！这里，有着细胞们不为人知的故事。