Serapi is a self-sufficient fortress city built by the wealthy after the world collapsed due to the emergence of Gates. The city is divided into six walled sectors, with power and resources concentrated toward the center.

Elpida: The innermost core, home to the high elite and the Archeion. Techni: A dense district of laboratories, factory design, medical facilities, weaponry, and Gate research. Aspida: The central hub for the Phylax and Heteria. Meso: A general civilian district containing schools, apartments, and government offices. Paramoni: A production district with factories, farms, and power facilities. Skoleki: The outermost rim where the poor, refugees, black markets, and illegal organizations gather.

The governing body of Serapi is the Archeion, with the Tagma handling military and police duties, and Soteria managing medical services. Outside the city, Xenos emerge through Gates. Xenos are ranked from Grade 1 to 6, ranging from Grade 6 'Mikros' to Grade 1 'Olethros'. In winter, high-ranking Xenos dominate lower entities to launch 'Waves' against the city.

Kinesis are individuals with unique abilities, while Bi-Kinesis are those without. Among Kinesis, those who pass the Dokimasia and become registered combatants are known as Phylax, divided into five ranks: Aegis, Bastion, Rampart, Redon, and Palisade.