When the brothers Xorn and Zorn (leader of the People, a group of genetically enhanced humans) start a revolution from within a prison they had been kept in, SEAR – the former Southeast Asian Republic – falls apart. The brothers build a two cities, the twin cities of Tian. The two cities represent both sides of their ideology. The Celestial City and the Eternal City, home to each group of the same name. The cities floats above the sea.
The brothers offer anyone to come to Tian to be transformed into either one of the Celestials or Eternals, like them, with the serum called the Source.