In Final Fantasy VII, the city built around a giant reactor is Midgar.
Midgar is the immense industrial metropolis that dominates the opening of Final Fantasy VII. Shinra Electric Power Company constructed the city around eight enormous mako reactors, which draw energy from the planet’s life force. The reactors supply power to Midgar and support Shinra’s economic and political control over much of the world.
The city is divided into an upper plate, where wealthier residents live, and lower sectors beneath it. This structure reflects the game’s central social conflict: the upper city enjoys Shinra’s prosperity, while communities below endure pollution, darkness, and the danger of living under the plate. Sector 7 is home to the original headquarters of AVALANCHE, the eco-terrorist group opposing Shinra.
Midgar is not simply a backdrop. The opening bombing mission takes place at one of its reactors, and the plate collapse in Sector 7 becomes a major turning point. Nibelheim is Cloud’s hometown, Cosmo Canyon is associated with Red XIII and the study of the planet, and Junon is another Shinra-controlled city, so none fits the question.