Pyrefly

Pyreflies are an ambiguous, naturally occurring phenomenon that heavily influence the events of the computer role-playing games Final Fantasy X and Final Fantasy X-2.

Pyreflies are prevalent throughout the world of Spira and are closly linked with the concepts of lifeforce and spiritual energy that the two games put forth. In fact, they are the form that disembodies spiritual energy takes.

Despite the allusion their name gives them to the real-world insect, pyreflies are not depicted as living creatures. Though they have been harnessed to many ill uses, in their inert form, they appear to lack self-awareness and any identifiable agenda. As such, they are nothing more than an aspect of nature.

Nature
Pyreflies appear to exist in one of three distinct states. When inert, their first state, they manifest as insubstantial points of light, similar to the fireflies from which their name is partially inspired, which float aimlessly within a particular area of attraction. Inert pyreflies also generate a delicate, audible sound. In their second state, concentrations of pyreflies can take the form of physical creatures, yet remain insubstantial, reminiscent of ghosts. In the final state, pyreflies can take on the properties of solid matter. It is known, for example, that the 'body' of Sin consisted entirely of a vast quantity of pyreflies, apparently compressed together using gravity magic.

Pyreflies and death
In Final Fantasy X, when a person dies, their body cannot simply be laid to rest, first their spirit or lifeforce (represented by pyreflies) must be released from the body and given "guidance" to return to the Farplane. A Summoner is required to engineer this "guidance," in a ritual known as a "Sending." If the Sending is not performed, then the body's spirit is said to be trapped in the physical plane, growing first envious then hateful of the living; the hatred eventually grows strong enough to manifest one's pyreflies into a fiend, a fully substantial and dangerous monster. It is not known whether all of the recently-deceased must be Sent, or just those who have suffered a violent or untimely death.

In some cases the transformation into a fiend does not occur with the unsent dead. If the deceased possessed a powerful will and strong feelings regarding an unfinished purpose in the world of the living, an individual's spirit can remain strong enough post mortem to manifest their pyreflies into a physical form in the image of the deceased's former body. Such beings as this, who may act and function for the most part as they did in life, are referred to as "Unsent" and may be benign or malicious, depending upon the nature of the individual. The Unsent are usually unwilling to enter the Farplane using the various gateways that exist in Spira. This is believed to be because they may be physically unable to leave once they've done so and are wary of taking the risk. They are also vulnerable to the effects of the Sending, which can banish the disembodied spirit to the Farplane and disperse their pyreflies, usually no matter how strong the will that binds them. Note that there have been two notable exceptions to the previous matters:

1) In the case of Maester Jyscal Guado, his spirit manifested in his living form twice after death and emerged from the Farplane, despite having been Sent prior to both occasions (the first time by his son, Maester Seymour, and the second time by High Summoner Yuna). His first reemergence is seen in Final Fantasy X when his form walks out of the Farplane gate in Guadosalam. His second return is discovered in Final Fantasy X-2 in the Via Infinito beneath the city of Bevelle.

2) In Final Fantasy X-2, the Unsent known as "Shuyin" enters the Farplane of his own volition and has little to no trouble maintaining his form there.

Another exception to dying without becoming a fiend in the absence of being Sent is rather unique in that it still results in one's spirit finding its way to the Farplane. Apparently, one who accepts death while still alive will travel to the Farplane after death without any assistance. This is seen in the cases of both Tidus' mother and Yuna's father, the latter of whom was High Summoner Braska, a Summoner who willingly gave his life in a battle with Sin.

The Sending
When a Sending is performed, its effect appears to be to transfer sentient lifeforce to the Farplane; the lifeforce, if any, of the flora and fauna are not affected (it can be inferred, in fact, that such wildlife as well as the planet itself draw energy from the lifeforce contained within the Farplane). Fiends, whose souls have apparently been completely subsumed by hatred, are subsequently not affected.

A Sending, therefore, is known to affect the following:
 * the lifeforce/soul/spiritual energy of a recently-deceased, self-aware creatures (humans and the Guado, at least, are shown to require Sending)
 * Unsent beings, ie, those the spirits of whom have remained on the physical plane after death and retained the purpose of their former lives.

Interestingly, during a Sending pyreflies are shown to emanate not only from the dispersed "bodies" of the Unsent, but also from the recently deceased. This is an indication (confirmed by the Final Fantasy X Ultimania Omega Guide) that pyreflies are always present in the bodies of the living, as well as in everything else in Spira.

The Farplane
The people of Spira have long enjoyed the ability to make occasional visits the Farplane, primarily using the gateway that exists within Guadosalam, the purpose of which is to call up their memories of those who have died. Since the Farplane is naturally filled with vast quantities of pyreflies, some are attracted to the evoked memories and give them partial substance, forming a ghostlike image of the subject being recalled.

The physical plane
The attraction pyreflies show to the energy of strong memories is not restricted to the Farplane, nor are the spirits of the dead necessarily required to manifest their spiritual energy in order to interact with the living on physical terms. These two phenomena have been displayed at length, resulting in the unsettling ability to perpetuate a spirit's memories against their will, as well as the equally disturbing concept that the dead may possess the living.

1000 years before the events of Final Fantasy X-2 take place, the game's primary antagonist Shuyin was caught and killed by agents of the Bevelle army while attempting to operate their superweapon, Vegnagun. His attempt to do this was a result of desiring to destroy Bevelle, as he believed he would be unable to save his captive love, Lenne. Reunited for a brief moment before death, Shuyin didn't hear Lenne speak the words "I love you" to him before his life faded. This -- and his feelings of hatred toward Bevelle, and the feelings of self-loathing that emerged due to his self-perceived failing of Lenne -- resulted in his spirit becoming full of hatred and despair. His spirit wandered until it came to inhabit a cave beneath Mushroom Rock Road, where it wallowed in despair and loathing. The powerful emotions emitted by his blackened spirit attracted a multitude of pyreflies. The pyreflies present at the location were imprinted with his despair and painful memories and refused to allow them to fade. Over time, Shuyin's painful memories and the feelings they evoked fused with the pyreflies in the area, granting self-awareness of sorts to them and they even began to act on their own to an extent, active and aware even when the original Shuyin's consciousness had left the cave, hidden within the body of a young soldier named "Nooj."

It is here that we see the second disturbing phenomena represented. Shuyin's spirit possessed Nooj and used his body as a vessel, forcing him to shoot and critically wound his comrades on one occasion, and nearly forcing him to do so a second time two years later. It was then that Shuyin's spirit abandoned Nooj and possessed Nooj's former comrade, Baralai, using him as a new vessel in the operation of Vegnagun.

Shuyin's despair and desire for destruction were so great that it even influenced the Fayth to act as agents of destruction. After being freed from this dark influence, the Bahamut Fayth -- the chosen representative of the Fayth as a whole -- spoke to Yuna on the Farplane and informed her that Shuyin was merely a "shadow" of sorts. The person he was had long since faded, consumed by despair, hate, and the desire to disappear and be free of his painful memories, but without the means to do so, constnatly reminded of his "failure" of Lenne and their painful parting by the very pyreflies that were drawn to him and imprinted with his dark memories. This had driven nearly all the humanity and compassion he once had from him, save solely his love for Lenne. Being unable to find solace from the despair of a millenium, he sought the destruction of the whole world as a means to find freedom.

It was to this end that he sought to use Vegnagun. Possessing Baralai, he attempted to use the mechanical beast to fire a beam at the surface fueled by the Farplane's energy, a single blast that would have brought an end to the entire world. Yuna and her allies successfully decommissioned the technological behemoth, however, leaving Shuyin with no means to employ his destructive ambitions. Then, mistaking Yuna for Lenne, he emerged from Baralai's body and began to approach Yuna, only to realize a moment later that she was not Lenne, driving him into a final anger-fueled attack upon her. In the end, he would physically manifest his spiritual energy on the Farplane and battle Yuna and her allies. His spirit was defeated and then convinced to rest on the Farplane by the spirit of Lenne. She emerged from Yuna's Songstress Dressphere (the crystalized form of Lenne's spiritual essence) to put Shuyin's despair to an end with her love and the offer that he rest with her.