Tokyo Kingdom City. An artificial island 10km above the Gulf of Tokyo.
Back in the day, the Japanese government invested a fortune to build a second metropolis. However, the project was completely halted over a decade ago, and it has since become a virtually abandoned, illusory city.
It has now degenerated into a "Demon City"—a chaotic mix of criminals, mafia, demons, and foreign corporations—becoming a haven for lawless and illicit individuals.
Those with power rule over the citizens, and the citizens follow those with power. Under that order, the countless criminals and outlaws of Tokyo Kingdom City have been allowed to survive—
—Peace and order are no more. Demons, who once ruled over humans and made them obey, tamed them, suddenly began attacking those very humans.
......However, there were those who opposed them—the Taimanins and UFS troops who infiltrated Tokyo Kingdom City. Prioritizing the protection of citizens, the joint forces of the Taimanins and UFS troops retreated, eventually establishing the final line of defense at the entrance of the Tokyo Kingdom Bridge—the only remaining route connecting the city to the mainland.