Welcome to Gaia; a world run by the Shinra Electric Power Company from their headquarters in the city of Midgar. A city of two halves; one of power, riches & influence above ground on a giant plate and one of extreme poverty, violence & exploitation in the slums where the light is blocked by the plate above.
Shinra came to power through their Mako energy production; using the planets own energy (Known as the Lifestream), Shinra refine the raw material into Mako through their Mako Reactors and this provides electrical power to the inhabitants. This has allowed Shinra to become a huge influence on the politics of the planet and are not afraid to use under-handed methods to maintain their place.
To the common folk, Mako is amazing and without draw-back, but not everyone feels this way; AVALANCHE is a rebel / terrorist group who see Shinra using the planets Lifestream to make Mako as killing the planet and they plan to destroy the eight Mako reactors in Midgar to put an end to Shinra. When they hire a mercenary named Cloud, who claimed to be an ex-SOLDIER, to destroy a Mako reactor in Midgar, a chain of events will be set in motion that will change destiny and the future of he planet...