In the urban civilization floating in space, "Cocoon", lived four students of the United Nations University: Arata, Tara, Caesar, and Louis. These four were a new breed of human, who had undergone the process of neoteny and adapted to the space age. The entirety of human relationships are decided by contracts, and while some humans get to live for hundreds of years, others are not quite so lucky. One day, these four meet a girl with green hair in the red light district, and thus our story begins.