Jamais Vu

Jamais Vu was an event that occurred at an unknown point in time, in an alternate universe.

Prelude
A Soviet commuter jet ended up crashing in the ocean near the United States Prison Facility on the southern tip of Cuba, with something coming out of the wreckage before it sunk. Telecommunications at the base were blacked out for a full 24 hours, yet when they were fully restored, the only communications afterwards were a suspicious "conditions normal" and nothing afterwards. It was later confirmed that the base had been overrun by unknown life-forms only identified as Body-Snatchers that kill people and steal their identities.

Finding the events suspicious, a CIA contact hired the private military company, Militaires Sans Frontières to investigate and exterminate any and all Body-Snatchers at the base. MSF's leader Big Boss was briefed about the event by his lieutenant, Kazuhira Miller. As the subject matter and mission was far beyond even Big Boss's capabilities, they ended up hiring a time-travelling cyborg, Raiden, to partake in the mission in their stead, as his cybernetic body made him immune to Body-Snatchers taking him over. In exchange, MSF would supply Raiden with the XOF patches they had collected in a prior operation.

The mission
Sometime later, during a storm at 00:01, MSF arrived via chopper at the prison facility. Big Boss then showed Raiden a watermelon containing an XOF patch on it to remind him that this was their payment should he succeed. After Raiden activated his Augmented Reality visor, he then stood up. Big Boss then offered Raiden his sword, but he declined, instead being content with the firearm he had received. Miller then reminded Raiden that most of the Marines on the base are most likely Body-Snatchers inhabiting human bodies, and as such not to expect many survivors. After arriving at the jump point, pausing only to load his gun, Raiden proceeded to jump out of the chopper. The chopper then departed, although not before Miller relayed to Raiden that the fate of the world is in his hands, also telling him to mark the personnel to separate the soldiers from the snatchers.

Raiden found a soldier near the watchtower. Although the soldier was not a Body-Snatcher, Miller nonetheless ordered Raiden to interrogate the soldier for anything he knew, finding the man suspicious. After learning from the man the location of all the personnel across the base, Raiden managed to spot a Body-Snatcher. He then killed him. After hunting down and killing all 12 confirmed Body-Snatchers on the base and neutralizing the non-Snatcher soldiers, Raiden prepared for extraction from the MSF chopper. Before he could get himself extracted, several waves of Body-Snatcher reinforcements unexpectedly appeared, forcing the chopper to keep its distance while Raiden wiped them out, including several manning vehicles and choppers. Upon confirming all of them were wiped out, Raiden boarded the chopper and departed from the area.

Aftermath
As promised, Raiden received the XOF patches, with Miller considering meeting Raiden again in the future. Miller then debriefed Big Boss after the crisis was over, although the Body-Snatchers' origins were unable to be determined. Miller then expressed hope that they didn't have anything bigger planned, and that the whole situation seemed like a bad dream.

Behind the scenes
Jamais Vu is the extra op mission that was used for the Xbox 360/Xbox One versions of Metal Gear Solid V: Ground Zeroes, unlockable by collecting XOF patches.

There were several references to Metal Gear Rising: Revengeance throughout the mission:
 * The chopper that delivered Raiden to the base had the Platinum Games logo on the fuselage of the chopper.
 * The opening song for Metal Gear Rising is heard in the background as Raiden arrived at the intrusion point.
 * During the final moments of Jamais Vu, the Hammerhead boss theme could be heard as Raiden held off the advance of the remaining Body-Snatchers as well as during the credits.
 * During the post-mission debriefing and rewards tally, the menu/post-mission tally theme from Metal Gear Rising could be heard.
 * After Raiden managed to wipe out all of the reinforcements for the Body-Snatchers, George can be heard saying "Cowabunga."

The narrative at the beginning said the following: "Our galaxy consists of some 300 billion stars. Around half are orbited by planets, and it is said that on average, conditions on two of a star's planet are suitable for life. No great leap of imagination is needed to believe the universe must be home to a myriad of life forms. But what sorts of intelligence would develop on these worlds? That is truly beyond our imagination. What's more, we cannot say that our universe is the only universe. At the quantum level, until a wavefunction collapses upon observation, Schrodinger's cat is alive and dead as a superposition of states. The moment observation occurs, these two possiblities branch into separate worlds, with the universe continuing to split infinitely. If the universe splits without end, it's possible it could eventually recreate scenes from the past. And if those things played out differently, it wouldn't negate what happened in our reality - a paradox would simply mean another future. The following is one possible story in one possible universe, born of paradox, after paradox, after paradox..."

The narrative before the chapter, as well as their comments about XOF patches, indicated that the mission took place in an alternate universe where MSF not only didn't end up devastated by XOF, but also wiped out the XOF unit.

In psychology, jamais vu (French for "never seen") refers to the phenomenon of experiencing a situation that one recognizes in some fashion, but nonetheless seems very unfamiliar.