The world is on the brink of an ecological catastrophe. The economy is dominated by Shinra, Inc., a multinational monster of an energy company, which even has its own armed forces (aptly named SOLDIER) and secret police (called the Turks, for some obscure reason). It uses Mako–essentially the life-force of the planet–as an energy source and has its HQ in Midgar, a sprawling, overcrowded, over-polluted megalopolis (by far the largest city in the world). A small resistance group called AVALANCHE, led by a man named Barret, decides that enough is enough. They embark on a series of missions to sabotage Mako reactors, firmly set on saving the planet and ending Shinra’s tyranny. Since they’re a little short on numbers, they hire a mercenary called Cloud, who claims that he used to be a SOLDIER First Class, essentially the elite of Shinra’s armed forces. The first reactor explosion goes off without a hitch, but exposes the group to Shinra’s eyes. So on the second mission, things go pear-shaped, Cloud gets separated from the others and encounters a mysterious girl called Aeris/Aerith who proceeds to get kidnapped by the Turks. Shinra cracks down on AVALANCHE, and its surviving members accompany Cloud to Shinra’s HQ to rescue Aeris/Aerith. However, in the middle of the infiltration, the president of the company is unexpectedly assassinated by Sephiroth, a legendary hero of SOLDIER, previously presumed dead. This leads the gang to realise that there’s a much more serious menace hanging over the world than just a money-grubbing corporation.
As you can see, this is a far cry from the castles, princesses and dragons of the previous FFs. While in essence, the main issue remains the same–preventing an evil force from destroying/ruling the world–, thematically, the game suddenly moves a lot closer to home, bringing ecological and technological issues to the fore.