The story of Final Fantasy VII begins as the protagonist, Cloud Strife, joins the anti-Shin-Ra organization AVALANCHE in a bombing raid on one of eight mako reactors that surround the city of Midgar. The mako reactor is soon destroyed and the group makes their way back to their base. En route, Cloud encounters Aeris Gainsborough, a flower merchant. During their next mission, AVALANCHE is trapped by President Shinra and a robotic guard before they can escape the mako reactor that they have rigged to explode. Although they defeat the guard, the reactor's explosion sends Cloud hurtling from the upper levels of Midgar into the slums below. Falling through the roof of a derelict church in Sector 5, he lands on a flower bed unharmed, where he is formally introduced to Aeris. Cloud soon agrees to take a job for Aeris as her bodyguard, an agreement prompted by the arrival of operatives of the Shin-Ra Company's Turks organization, who have been ordered to capture Aeris.

After the player defends Aeris from her would-be kidnappers, Cloud accepts her offer to show him the way back to Sector 7. Along the way, she reveals that her first boyfriend had been a 1st Class SOLDIER, as Cloud claims to have been. Soon, the two spot Tifa entering Wall Market, an area of Sector 6 infamous for criminal activity, to which they follow her. After infiltrating the mansion of crime boss Don Corneo, the three learn that Shin-Ra has discovered the location of AVALANCHE's hideout and plan to collapse the upper level of Sector 7 onto the slums below. Despite AVALANCHE's efforts to prevent it, Shin-Ra successfully destroys Sector 7, killing its population and three members of AVALANCHE. The Turks finally capture Aeris, who the player learns is the last living member of an ancient race called the "Cetra". The Cetra, it is explained, are closely attuned with the planet. Therefore, President Shinra believes that Aeris can lead him to a mythical land of fertility known as the "Promised Land", which Shin-Ra expects to be ripe with mako energy that can be easily harvested.

As the only remaining members of AVALANCHE, Tifa, Barret and Cloud infiltrate Shin-Ra's headquarters to rescue Aeris. After freeing her and the lion-like Red XIII, who joins the party, they are able to escape when most of the personnel in the building — including President Shinra — are slaughtered. Finding the body of President Shinra skewered by a long sword, Cloud suspects the acclaimed SOLDIER Sephiroth has returned from his presumed death. These suspicions are confirmed by an executive spared during the massacre, who claims to have witnessed Sephiroth murder the president and state that he would never allow Shin-Ra to claim the Promised Land. The party also learns that during Sephiroth's attack on Shin-Ra, the headless body of a creature named "Jenova" disappeared from the building's research facility.

While President Shinra's son, Rufus, assumes control of the Shin-Ra Company, AVALANCHE pursues Sephiroth across the planet, fearing his intentions for the Promised Land may be more destructive than Shin-Ra's. During this pursuit, the group gains several new members: Yuffie Kisaragi, Cait Sith, Vincent Valentine and Cid Highwind. As the journey progresses, each member of the group must come to terms with personal conflicts from their past, and the full scope of Sephiroth's plan is eventually revealed to the player: if the planet is significantly damaged, the Lifestream within will gather at the point of injury, attempting to heal the wound. Sephiroth explains that he intends to use a powerful spell known as "Meteor" to fatally injure the planet, inciting a reaction in the Lifestream to heal the wound before it can cause the planet's destruction. Entering the fissure created by the meteor's impact, Sephiroth would be able to merge with all the energy of the planet, granting him god-like power over it. At an ancient temple erected by the Cetra, AVALANCHE attempts to undermine Sephiroth's plot by claiming the Black Materia needed to activate Meteor, but Sephiroth displays a mysterious power over Cloud, forcing him to relinquish it.

Fearing that Sephiroth may soon cast Meteor, and having gained a greater understanding of her heritage from scholars in Cosmo Canyon and the memories of her ancestors in the Cetra's temple, Aeris sets off to stop him on her own. Concerned for her safety, AVALANCHE follows her to the northern continent, where the player must enter an ancient Cetra city. After finding Aeris praying to the planet for aid, Sephiroth, unseen, begins affecting Cloud's behavior once again, and attempts to force him to kill her. Though Cloud is able to resist Sephiroth's command, Sephiroth himself appears and impales Aeris, killing her. After laying her body to rest, the surviving characters resolve to defeat Sephiroth and avenge her.

Soon after, Sephiroth begins causing Cloud to doubt his memories and insists that he is not a real human, but rather a specimen created from Jenova's genetic material by Professor Hojo of the Shin-Ra Company. Jenova, the player learns, was an interstellar creature who crashlanded on the planet approximately 2000 years earlier, arriving via travel on a meteor. This collision formed a large impact crater, grievously harming the planet. Jenova soon emerged from the crater, intending to infect all living organisms on the planet with a virus that would induce insanity and incite monstrous transformations. Among its victims were most of the Cetra, who were approached when Jenova used its mimic abilities to appear as their relatives. Attempting to defend itself, the planet created giant monsters called "WEAPONs", while the majority of humans fled rather than fight Jenova. However, a small group of Cetra survivors fought to defend the planet and managed to defeat Jenova, confining it within the fissure created by its landing. Afterward, the WEAPONs entered hibernation to await any future threat that could harm the planet. Eventually, the mummified remains of Jenova would be unearthed by Professor Gast, a researcher for the Shin-Ra Company. Mistaking the creature for a Cetra, Gast was given authorization to conduct an experiment to artificially produce a Cetra by combining cells from Jenova with the fetus of an unborn child.

Five years before the present-day events seen by the player, Sephiroth learned that he was the product of this experiment. However, unaware of all details involved, he concluded that he had been produced solely from Jenova's genetic material and that he was a Cetra. Enraged, he burned the hometown of Cloud and Tifa, Nibelheim, intending to kill all descendants of those he believed had abandoned his ancestors in the defense of the planet. According to Cloud, he confronted Sephiroth during this massacre, after which Sephiroth vanished under unknown circumstances and was presumed dead until his reappearance in the Shin-Ra building. Sephiroth now tells Cloud that he was not in Nibelheim, showing him images of a 1st Class SOLDIER with dark hair who occupies Cloud's place in his memories. With Tifa unable to refute Sephiroth's claims, Cloud breaks down and allows him to cast Meteor, resulting in the WEAPONs' awakening. During the earthquake that follows, Cloud is separated from his companions and falls into the Lifestream.

As the meteor summoned by Sephiroth slowly approaches the planet, the Shin-Ra Company focuses its efforts on protecting humanity from the WEAPONs, who have begun to perceive everything as a threat to the planet. Meanwhile, AVALANCHE searches for Cloud, eventually locating him on a tropical resort island where he washed up following the casting of Meteor, they learn that he is in a catatonic state. Soon, the WEAPONs' destructive activity causes the island to split open, depositing Cloud and Tifa into the Lifestream below. There, she is able to reconstruct Cloud's memories and learn the truth about his past. Although the player learns that he is a real human being and had actually been in Nibelheim during Sephiroth's attack, he never actually succeeded in joining SOLDIER and only managed to attain the rank of private in Shin-Ra's military. The player learns that the previously-seen dark-haired SOLDIER is named "Zack", and was Aeris' first boyfriend. During Sephiroth's destruction of Nibelheim, Zack, Tifa and Cloud fought Sephiroth in Nibelheim's mako reactor. Although Tifa and Zack were defeated, Cloud and Sephiroth fatally injured one another. After decapitating the body of Jenova, which had been stored in the mako reactor, Sephiroth fell into the Lifestream, taking the creature's head with him. Rather than dying, however, his body and consciousness were preserved in mako inside Jenova's crater.

While Tifa was taken to safety in Midgar, where she joined AVALANCHE, Cloud and Zack were among the wounded survivors who were apprehended by Shin-Ra as part an elaborate cover-up of Sephiroth's massacre. Professor Hojo subjected these survivors to an experiment, in which he performed the same enhancements given to members of SOLDIER. However, because Hojo conducted the experiment without any concern for the subjects' mental capacities to handle the procedure, all but Zack entered a comatose state. Nearly five years later, Zack broke free from his confinement and took Cloud with him. The player learns that the procedure used to enhance members of SOLDIER involved both mako showers and the injection of cells from Jenova. The alien cells inhabiting Cloud's body allowed his mind to construct a false persona, built around Zack's behavior, fighting style, and description of Sephiroth's destruction in Nibelheim, but they also allowed Sephiroth to modulate his behavior. The cells' inherent ability to duplicate information led Cloud to believe that he had been the 1st Class SOLDIER in Nibelheim, as Zack was shot and killed outside Midgar by pursuing Shin-Ra soldiers, shortly before the beginning of the game. Afterward, Tifa discovered Cloud, who was wearing Zack's spare uniform, and offered him a job with AVALANCHE.

With the truth revealed, Cloud awakens and rejoins AVALANCHE. Soon, the player learns that in her final moments, Aeris was casting a spell known as "Holy", the only means of opposing Meteor. Though she succeeds, Sephiroth's focused will prevents the spell from taking effect and has been restraining it since. Deciding that humanity must be protected from the WEAPONs before Sephiroth can be approached, Shin-Ra and AVALANCHE destroy the WEAPONs, but nearly all of Shin-Ra's executives are killed in the process. Among the few survivors are Reeve Tuesti, revealed to be the repentant controller of Cait Sith, and Professor Hojo, who is revealed to be Sephiroth's father. He explains that he and his wife were assistants to Professor Gast, and offered up their unborn child as a test subject to research involving Jenova. When Hojo attempts to help Sephiroth to gain mastery over the Lifestream afterward, AVALANCHE is given no choice but to fight and kill him.

With each member of AVALANCHE at peace with their past and all other opponents defeated, the group travels through the mantle of the planet to its core, where they succeed in defeating Sephiroth and freeing Holy. However, due to Meteor's already close proximity to the planet's surface, Holy is unable to destroy it alone. Selected as Meteor's target, Midgar is almost completely destroyed by the storms that spawn from its presence. However, sent by Aeris' spirit, the Lifestream itself soon rises from the planet to aid Holy by pushing Meteor away, allowing Holy to destroy it.[58] During the epilogue that follows, the ruins of Midgar are shown five hundred years later. While the landscape had once been desolate due to Shin-Ra's operations, it is now a land of lush greenery.

(Reference: http://na.square-enix.com/games/ff7/ )