Because Griever has decided to spend some time on Dear Mun, I figure I need to put some of the core info of Guardianverse somewhere online.
Cosmology
The core of Guardianverse is Lifestream cosmology. All planets have a Lifestream (some just call it by another name). One of the effects that Lifestreams are subject to is that legends literally come to life - if enough dying people believe in the same thing, it can gain it's own sentience and become a living spirit that can be summoned by specialist mages - Summoners.
There are a few ways a legend can gain sentience, the slow way, the quick way and the super-quick way.
The Slow Way
The slow way is that the legend slowly builds until it reaches critical mass and forms it's own sentience. The problem with this is that Summons who form in this manner are very disconnected from humanity, not feeling very much empathy for the living.
The Quick Way
The fast way is when the soul of a human that people associate with the legend joins the Lifetstream current dedicated to legend at a point just before the critical mass stage. The legend current will connect with that soul, investing itself in that soul and making it the sentience of the resulting Summon. This a quicker method than the slow method because it can shortcut the stage of attaining sentience by a fair amount.
These Summons have far more empathy for the living because they usually can still recall their life in the living world.
The Super-Quick Way
This is a similar situation to the quick way, but the person who becomes the sentience of the Summon is still living when it happens. This method can only happen in a society with a mass media system, at a time of war. The media spreads the legend, the war causes the deaths that swells the legend within the Lifestream.
The human in question has to be a particularly famous person who the media has connected to a legendary image that last even after many of the casualties of war have died. The gathering legend will connect to the person, giving them slowly growing para-magic abilities until a critical mass stage is reached and the person in question gains full control of the legend's power.
Usually the point where the person gains the full power of their legend, their soul is separated from their body. This theoretically kills the person, but their soul lives on as the new Summon.
World Rebirth
Another major detail is that worlds are reborn. The usual method is that a WEAPON is created to carry the Lifestream away from the dying world to start again elsewhere*. Due to the nature of this process, the only entities that are capable of surviving this process are the Summons.
[* As shown in Dirge of Cerberus.]
There are four known worlds in Guardianverse - FF4 Earth, Spira, FF7 Gaea, and FF8 Terra.
When Earth finally came to it's end, the Summons had to abandon their living bodies and become pure spirits to survive the transition. With the guidance of their eldest members who were already spirit-Summons, they successfully made the transfer, eventually establishing the world of Spira.
The Summons have a certain amount of influence on how the Lifestream shapes itself when it establishes itself on a new world. After all the trouble they had with the Great Crystals, the Summons tried to influence the Lifestream to not need Crystals to stablize it. This had a drastic effect of making the resulting Farplane a very chaotic place with very little control.
This chaotic nature gave rise to Fiends. The chaotic nature of the Farplane also makes it increasingly hard for Summoners to reach the Summons and they eventually abandon the traditional method of summoning when Aeons are invented by a mage in Zanarkand.
This begins a period of almost two thousand years of pain and loss for the True Summons - the original Summons from before the invention of Aeons. Those who survived best were the Summons that had Aeons adopt their names, legends and characteristics. Ifrit, Shiva and Bahamut's brood did well, with Leviathan later on needing Bahamut's support after Asura's death.
The end of this period started with Yuna's pilgrimage, with her and her team ridding the world of Sin and Yu Yevon, letting the Fayth go to their long-deserved rest. Later, it was Yuna herself who made first contact with one of the True Summons. The problems involved with the constant problem of fiends needed the talents of Summoners again, causing Yuna to try and seek out the Aeons again. She was guided by the fayth of the Aeon Bahamut to Tiamat, a dragon that was one of the True Summons and NEO Bahamut's daughter.
Once the first contact was made, more Summoners started seeking contact with the True Summons, giving their legends the boost they needed to recover the period of famine they had suffered.
After Spira started growing too old, the move to a new planet was planned and executed. The Summons, wanting to correct the mistake they made with Spira, allowed the Lifestream to take on a bit more of the crystal system it had with Earth. This turned out to be a far more stable system than Spira had with none of the pyrefly or fiend problem the Farplane was rife with.
Gaea's biggest problem came from outside - an alien organism crashed into the planet and started infecting the population, becoming known as the "Crisis from the Skies". The early population - the Cetra - were almost totally killed off trying to seal the Crisis away, leaving less Lifestream-sensitive humans as the majority population. The Crisis became a problem again when it's body was discovered and experimented on.
The real problem came when a genetic hybrid of the Crisis (also known as Jenova), Sephiroth, realized what he was and was driven mad by it, later attempting to destroy the world in an attempt to become a god be absorbing the Lifestream.
In the aftermath of that, the Lifestream was infected by Jenova's presence, through the geostigma disease, causing major problems for the Summons who were fighting for their own lives, trying to remain free of the infection.
In the middle of this crisis, a digital ghost of the scientist responsible for Sephiroth - Hojo - tried to awaken Omega WEAPON - the Lifestream's transport to a new planet. This attempt was stopped by Vincent Valentine, the carrier of the spirit of Destruction, Chaos (a Summon formed during the first Jenova crisis 2000 years before).
This turned out to be a good thing ultimately for the Summons, as the old Omega had not been able to cope with Geostigma. The new Omega that was formed as it's replacement was formed with an inbuilt ability to filter geostgma-affected Lifestream from unaffected Lifestream.
When this Omega was eventually awakened to carry out it's task, it did the filtering in flight to the new planet, choosing a world that had a large moon. It deposited the Dark Lifestream (the geostigma-affected Lifetsream) on the moon, before carrying the pure Lifestream to the planet below to start again.
As a side effect of separating the Lifestream, the Dark Lifestream on the moon gave rise to a population of various dangerous monsters of only semi-sentient nature (at best).
An unknown factor involved however with Terra is that the planet and it's moon sometimes aligned in a manner than formed a flux tube that could allow the safe transferal of matter from the moon to Terra's surface. This did not become a problem until the moon's monster population started to reach substantial levels, at which point monsters started being able to safely transfer from the relatively barren moon to the fertile world of Terra. These events, that eventually came to be known as the "Lunar Cry" due to the eye-like formation of the gathering monsters as the flux tube starts to form, were disastrous for Terra's population, suffering through the resulting flood of fierce monsters being dumped on them.
Added to the occasional havoc of the Lunar Cry, Terra suffered another problem - one of ironic similarity to Gaea's problems with Jenova. An alien enitity was accidentally caught in a Lunar Cry and trapped on Terra. This being infected a human and became known as the great Sorcerer Hyne. Hyne's abilities allowed him free access to the power of the Lifetsream, but the strength of these powers were so strong that it was causing strain on the planet as a result. The Summons formed a resistance, calling on human allies to fight Hyne. Also called upon were the first WEAPONs born on Terra, called up to fight the Sorcerer.
The forces gathered by the "Guardian Forces", as humans had come to call the Summons, eventually defeated Hyne, but could not totally dispel the entity that had given him his powers. Said entity however was split up into numerous pieces and absorbed by random humans who became Sorcerers and Sorceresses, with women seeming to be the more receptive. These fragments could not be absorbed by the Lifestream so whenever a sorceress died, her soul was not allowed to return to the Lifestream until the sorcerous powers were passed on to a receptive person.
For the most part this did not present too much of a problem as the split of the sorcerous powers meant no one person could cause a strain on the Lifestream as Hyne had, but the Elder Summons foresaw the time when those fragments of sorcery would come together again in one person, since the most receptive recipient of a Sorceress's powers would always be another sorceress.
This issue came to a head far sooner that the GFs were expecting when a Sorceress in the distant future, Ultimecia, started reaching back through time in an attempt to collapse the whole time continuum into a temporal singularity she referred to as Time Compression.
It was at this point the GFs started to take extra notice of Squall Leonhart, a newly qualified member of SeeD - and para-military organization that acted as mercenaries for hire, but were originally created to fight evil and amoral sorceresses.
The Guardians: Cast List of Guardianverse
The real centre of Guardianverse is the GFs who were humans at the beginning of their lives, and in particular, Squall Leonhart, who goes through the super-quick process and becomes the GF Griever.
The Eldest Summons
Back in the lifetime of Earth (FF4), Summons had lives in material bodies, living just like humans. The main difference between them and humans however is that the Summons could be called by Summoners and their spirits would be drawn from their bodies to aid the Summoner. They formed bonds with Summoners they were compatible with and would allow that Summoner to call them whenever needed.
When a Summon died, it was not the end of them though. If they were a well enough known Summon, they could carry on as a Spirit Summon, being called by Summoners they found worthy. A good example of a Spirit Summon was Odin, the Summon born from the old king of Baron, who had Mist blood in his line. The people of Mist - Summoners all - had in ages past crossbred with the Summons themselves.
Summons can live very long lives, not just because of the time dilation their cave community can be subject to, but also because of their strong links to the Lifestream. The strong a Summon's legend is, the strong the Summon and the longer they can live in their material body.
There is one major legend of note in Summon history - the legend of Bahamut and his two vassals, Leviathan and Ashura. Bahamut was High King of the Summons, with Leviathan and Asura, his vassals, serving as his Second and Third-In-Command respectively. The only problem was Bahamut had fallen in love with both of them. He did not however feel it was his place to disturb their happy marriage with his desires, but they in turn had noticed the feelings he tried to hide and loved him back. They confronted him and their relationship became a happy threesome.
When the Lunarian war (the civil war between Zemus's side who did not care for the primitive humans of Earth, and the more moderate side will to wait until the humans had grown wiser) was ended, the victorious Lunarians asked a favour of Bahamut, that he come to moon and guard it while they slept. Though this meant Bahamut would be separated from Leviathan and Asura, he agreed to perform this duty, taking with him only a few servants and leaving his lovers to rule the Summons on Earth.
During the time of the Crystal War, when Golbez, agent of the Lunarian Zemus, was taking the Great Crystals so he could open a gateway to the moon and free Zemus, one of Golbez's earliest acts was to kill off the Summoners of Mist. However due to Cecil Harvey's kind nature, one survived, a child by the name of Rydia. She was later taken by Leviathan and raised in time dilation in the Summon Cave by Leviathan and Asura so she would be able to aid Cecil's quest far better.
One of Golbez's other actions was the possession of Kain Highwind, Dragoon and close friend of Cecil's. The weakness Golbez used to control Kain was his love of Rosa, Cecil's girlfriend, and his jealousy of Cecil for having her.
The truth of Kain's feeling were eventually uncovered, revealling that it was not just Rosa, but also Cecil he loved. After all the events of the Wat were over and Kain left to pay his penance on Mount Ordeals, he found that Bahamut had also come to the mountain, having decided that Kain was a worthy soul to be taught the true history of the Dragoons - or as they had been once known, the Dragon Knights or Knights of Bahamut. In the process of learning from Bahamut, Kain started to realise that there were strong parallels between Bahamut's relationship with Leviathan and Asura, and Kain's own relationship with Cecil and Rosa.
Also seeing the same thing, Bahamut, with the aid of the ghost of Klu Ya (Cecil's Lunarian father), sytematically pushed Kain into eventually returning to Baron and working things out with Cecil and Rosa. Kain in a small act of revenge informed Rydia of where Bahamut was hiding, knowing she would let her adopted parents know and they would go and drag him home (an act that amused Klu Ya greatly).
Cecil, Rosa and Kain lived long content lives, though Cecil was eventually killed in another war that broke out. Kain stayed to support the Queen Mother, Rosa, until she died, then left Baron and found his way to the Summon cave where he became one of Bahamut's dragons - becoming the first known non-Mist human to become a Summon. The second human Summon was Princess Ellanora Farrell Highwind-Ya - Kain's daughter with Rosa - who became the dragon Summon Tiamat.
Kain and Ellanora then lived out the rest of the life of Earth as vassals of Bahamut, because they had become dragon summons.
TBC