Many years ago, at the end of a horrific world war, humanity sought refuge in six calm and flawless city-states... On the surface, at least. Shion, an elite inhabitant of the city-state No. 6, on the other hand, received a fresh perspective on the society he lives in as a result of a fortuitous encounter with a curious youngster named Nezumi. Nezumi turned out to be one of many people who lived in the dismal wasteland beyond the gates of the ostensibly utopian city. Despite knowing that the other child was a fugitive, Shion opted to take him in for the night and protect him, which had significant consequences: Shion and his mother lost their status as elites and were transferred abroad as a result of his actions, and the darker side of Shion emerged.