The Great Sephiroth Plan (セフィロス大作戦, Sefirosu Daisakusen?) was a planned military offensive against Sephiroth by the Shinra Inc. in Final Fantasy VII during the Jenova War. Although the combat stage of the operation was never implemented, the plan nevertheless played a significant role in the turn of events in the struggle against Sephiroth.
The Shinra Company has been chasing Sephiroth ever since he slaughtered President Shinra years after being assumed dead, and eventually learns that Sephiroth is planning to summon Meteor to wound the Planet. Both the company and AVALANCHE fail to stop the summoning, and Sephiroth sets up an energy barrier over the North Crater where he resides to prevent his enemies from interfering with his plans.
The company plans to use the Junon Cannon to destroy Sephiroth's energy barrier at North Crater. The cannon is moved to Midgar, where its fire power will be boosted by the city's mako reactors. The plan is to use the cannon to destroy Sephiroth's energy barrier before dispatching the entire Shinra army to North Crater to fight Sephiroth and to stop Meteor. The company has already made an ill-fated attempt to blow up the Meteor using Huge Materia loaded on a rocket, and the Great Sephiroth Plan is the last resort for the company to survive. The plan is mentioned by a soldier in Junon and some inhabitants in Kalm, but little is known about the strategy behind it.
Although the cannon fire destroys both the Diamond Weapon and Sephiroth's barrier, the energy beams from the Diamond Weapon hit Midgar and presumably kill Rufus Shinra. The company falls apart in the ensuing chaos, and it is unknown what exactly became of the Great Sephiroth Plan (although the lack of any Shinra troops at North Crater suggests a cancellation).
Although the operation is presumably called off, the destruction of Sephiroth's energy barrier allows Cloud's party to enter the North Crater and engage Sephiroth, leading to his defeat. It can be interesting to speculate what the outcome of the combat stage of the plan could have looked like if it had been implemented; the Shinra army was powerful, and since Cloud's party succeeded in beating Sephiroth on their own, it is likely the Shinra could indeed have won as well. However, this would have meant a continuation of the misuse of Mako energy, and the Weapons would have continued to pose a serious threat.
- Soldier in Junon: "I finally got orders to join the Great Sephiroth Plan. I even get to go on the Gelnika, too..."
"But, I'm just gonna ignore them. I wanna live to see the end of the world."
"If I'm lucky... There'll be a good place for me in the New World."
- NPC in Kalm: "Sephiroth put up a huge barrier around the North Crater".
"Rufus wants to use a mammoth cannon to smash the barrier."
"He plans to have Shinra troops rush in and attack Sephiroth after the barrier falls".