The Jenova War (ジェノバ戦役, Jenoba Sen'eki?) is an event in the world of Final Fantasy VII. Referred to by this name in the 10th Anniversary Ultimania, the conflict constitutes most of the main plot of Final Fantasy VII, in which the forces of AVALANCHE (led by Cloud Strife) and the Shinra Co. attempt to stop Sephiroth from destroying the Planet. The war lasts from December εγλ 0007 to 21 January εγλ 0008 and concludes with the defeat of Sephiroth by the efforts of AVALANCHE. Although AVALANCHE and Shinra share a common enemy, they remain hostile toward each other throughout the conflict and occasionally clash.
Approximately five years ago Sephiroth vanished during the Nibelheim Incident, falling into the Lifestream while carrying Jenova's head. He exerted his willpower over this extraterrestrial being, gaining the ability to control her cells, and began plotting to use the Black Materia to summon Meteor to strike the Planet. Sephiroth would absorb the Lifestream as it emerged to heal the wound caused by the impact, becoming a god-like being.
Cloud, the Shinra infantryman who threw Sephiroth in the Lifestream at Nibelheim, was used by Professor Hojo for scientific experiments before being broken out of captivity by Zack Fair and being taken to Midgar. Zack entrusted Cloud with his Buster Sword and Cloud took on a false identity based on Zack's memories. Cloud presented himself in Midgar as a former SOLDIER member now working as a mercenary, and was hired by his childhood friend Tifa Lockhart to assist AVALANCHE in their insurgency against Shinra. AVALANCHE's most successful operation is the bombing of Mako Reactor 1, but Shinra destroys Sector 7 to wipe out the organization's base of operations, killing three of AVALANCHE's six members. Aerith Gainsborough, who had assisted Cloud in returning to Sector 7 following a failed raid on Mako Reactor 5, is kidnapped by the Turks and taken to the Shinra Building. The surviving members of AVALANCHE infiltrate the Shinra Headquarters and free her, but are then captured and imprisoned by the Turks.
When Cloud, Tifa, AVALANCHE's leader Barret Wallace, and the Cetra Aerith Gainsborough are captured by Shinra, the remains of Jenova kept in the Shinra Headquarters take on Sephiroth's form and kill many of the employees. In the chaos the prisoner cells open. Seeing Sephiroth's Masamune near the corpse of President Shinra, Cloud realizes Sephiroth is alive, and AVALANCHE halts their struggle against Shinra and turns their efforts to investigating Sephiroth's return. AVALANCHE pursues Sephiroth across the Planet, who often appears before them via Jenova and unleashes mutated monsters formed from Jenova upon them.
AVALANCHE meets various fighters and travelers whose lives were affected by Shinra, and appeals to their cause, joining them into the war. After reaching the end of the Western Continent at Rocket Town, and gaining the help of Cid Highwind, a former Shinra pilot and mechanic, word reaches them of Sephiroth and Shinra being at the Temple of the Ancients, a Cetra ruin believed to hold what is known as "the ultimate destructive magic".
Cloud claims the Black Materia at the temple, but Sephiroth exerts mental control over him via the Jenova cells in Cloud's body (leftover from Hojo's experimentation on him), and seizes the Materia from him. Aerith, possessing the White Materia that can summon Holy to protect the Planet from Meteor, heads to the Forgotten City and pray for Holy. AVALANCHE follows her, and in the altar under the city, Sephiroth impales Aerith after Cloud narrowly avoids Sephiroth's mental commands to carry out the deed himself. The party is discouraged, but continues northward.
At the North Crater AVALANCHE sees Jenova as Sephiroth slaughter the Sephiroth Clones that have gathered at the site. After Jenova's main body is killed and the Black Materia reclaimed, AVALANCHE finds Sephiroth's true body in crystallized Mako. Sephiroth manifests before them and reveals the truth of Cloud's assumed identity. This shatters Cloud's mind, and believing himself a puppet to Sephiroth's will, he hands the Black Materia to him, who summons Meteor with it.
Shinra executes the first step in their Great Sephiroth Plan, a planned military offensive against Sephiroth. Shinra uses the Sister Ray cannon to pierce the energy barrier Sephiroth had erected over the North Crater allowing Cloud's party to descend into the Northern Cave. They have learned that Aerith had succeeded in calling Holy, but Sephiroth is containing it. The party kills Sephiroth, allowing Holy to move, and with the aid of the Lifestream apparently commanded by Aerith's spirit, the Meteor is destroyed over Midgar.
With the destruction of Sephiroth's physical body, he is once again cast into the Lifestream, continuing to exist in spiritual form. Jenova is nearly entirely destroyed, a few clusters of her cells surviving aside from those contained in experiments of the Jenova Project. Jenova's cells continue to endure in the Lifestream, resulting in the fatal plague Geostigma that culminates two years later when Sephiroth attempts to use it as part of another plan to resurrect himself.
Midgar is destroyed due to being at ground zero of the conflict between Meteor, Holy and the Lifestream, but through the efforts of Yuffie Kisaragi, Vincent Valentine, and the Turks, many residents evacuated in time. The survivors founded a new city on the outskirts of Midgar's ruins, called Edge.
The Lifestream's flow over the Planet shifted after Meteor's near-impact, causing mako reactors to no longer produce power. Feeling indebted to the Lifestream and Holy for sparing them, the people reduce their usage of Mako and Materia, products refined from the Lifestream by Shinra. Shinra's leadership is fractured due to the deaths of most of its executives in the war, but it survives albeit in a drastically weakened form.
- Final Fantasy VII 10th Anniversary Ultimania, p.031 (Translation)