Aselia, also localized as Aseria in the Game Boy Advance version of Tales of Phantasia, is the name of the world in which Tales of Phantasia takes place. It is also the setting used in its sequels Tales of Phantasia: Narikiri Dungeon and Tales of the World: Summoner's Lineage, as well as the combined world of Sylvarant and Tethe'alla from prequels Tales of Symphonia and Tales of Symphonia: Dawn of the New World.
Introduction of Life
Aselia was once a desolate planet, completely void of life and atmosphere. Elves from Derris-Kharlan discovered the planet and transplanted their World Tree, the Kharlan Tree, into the ecosystem, introducing mana and life to the planet. Many of the Summon Spirits of Derris-Kharlan were transplanted with the tree to manage the growth of life, and the Summon Spirit Ratatosk was tasked to be the guardian of the tree, controlling the flow of mana through monsters and the eight Centurions. The elves then took a cutting of the newly planted World Tree and replanted it on Derris-Kharlan, which could not survive without a World Tree of its own in order to regulate mana which was necessary for life on both planets.
The Kharlan War
Many years after life had flourished and evolved, and 5,000 years before the start of Tales of Symphonia. The Kharlan War occurred due to the advent of magitechnology, using powerful weapons such as the Thor's Hammer. The war lasted for at least 1,000 years, until Mithos the Hero and his party of followers successfully forged pacts with each of the Summon Spirits and created the Eternal Sword. Following the destruction of the Kharlan Tree, which created an imminent risk to all life that relied on its infinite mana, Mithos used the sword's powers of altering time and space to separate the planet of Aselia into two separate planets known as Sylvarant and Tethe'alla. The unified world could no longer survive through what little mana remained so the mana would have to be shared among the two smaller worlds.
Mithos set up a system where the Summon Spirits are split among the two planets and mana links were formed between the Summon Spirits of opposing elements. This system was designed to prevent either planet from accumulating too much mana, leading to that planet's civilization from advancing too far, which would lead to the reinvention of magitechnology and a return to war. In order to manage this balance of mana, a Chosen of the lesser planet is granted the right to start a Journey of Regeneration, in which he or she travels through each of the elemental temples and unlock the seals at each temple. This leads to the reversal of the mana links so that mana is redistributed away from the more prosperous world, leading to its decline while the lesser world's civilization is given the opportunity to progress forward. The process is repeated when that planet grows too technologically advanced, and the opposing world's Chosen goes on his or her own Journey of Regeneration. In the process of creating this system, Mithos knew that he had to prevent Ratatosk from interfering with his plan, since the system of mana links would prevent the rebirth of the Kharlan Tree and weaken Ratatosk considerably. Mithos openly betrays Ratatosk by attacking and trapping him within the Ginnungagap, leaving him to fall into a deep slumber until the mana link system is overthrown and the World Tree is revived.
Tales of Symphonia
During the Journey of Regeneration, initially led by the Chosen Colette Brunel of Sylvarant, the conspiracy of Cruxis to bind the two worlds together through mana links was discovered, along with its ulterior motive of reviving Mithos's dead sister Martel Yggdrasill through the bodies of each Chosen to succeed in her journey. The links were severed by Sheena Fujibayashi after forming pacts with the Summon Spirits, who had felt betrayed by Mithos's sacrifice of all mankind for the sake of his mad vision of the "Age of Lifeless Beings". He believed this would lead to the end of the racial discrimination that he and his sister suffered throughout their own journey to save the world during the Kharlan War. Through the efforts of Lloyd Irving acquiring the Eternal Sword, the worlds of Sylvarant and Tethe'alla were rejoined. The Mana Seed which had housed the Cruxis Crystal and spirit of Martel was planted, allowing the creation of a new World Tree protected by the new Summon Spirit Martel, who took on the name and appearance of Mithos's sister.
Tales of Symphonia: Dawn of the New World
Now that a new World Tree had been created, Ratatosk reawakened but remained trapped within the Ginnungagap. Extreme weather and climate changes occurred throughout the newly combined world since Ratatosk could no longer control his monsters, and most of his Centurions remained locked in their cores. Upon meeting Richter Abend and Aster, who entered Ratatosk's lair to request for him to try to fix the climatic weather situation, Ratatosk killed Aster and in turn was nearly slain by Richter. Ratatosk retreated into his core, which the Centurion Tenebrae took with him upon fleeing, eventually discovering Marta Lualdi who joined Tenebrae to unlock the Centurion Cores. Ratatosk himself re-materialized as Emil Castagnier, and he joined Marta and Tenebrae as they successfully reawakened all of the Centurions. Ratatosk eventually returned to his lair within the Ginnungagap, where he began to modify the role of mana within the world to eventually allow life to survive without it, a process which he states will take at least 1,000 years.
The Ragnarok War
As a whole once again, the planet of Aselia flourished. The people went through an age of industrial revolution, and eventually they learned once more how to master machines and magitechnology. Three major countries were formed: Fenrir, Odin, and Thor. The three countries lived in relative harmony for some time, but eventually, Odin and Fenrir started to engage in open conflict with each other, and Thor prepared itself to try to maintain peace between both countries. It was then that a comet known as Samier was spotted in the sky, possibly heading straight for Aselia. Scientists denied that it would reach them, claiming that their supercomputers told them that the comet's tail may graze the planet, but there is zero chance of a direct hit. It is not known whether this was simply a lie used to calm the people or whether their calculations were wrong, but either way, the comet did hit the planet, directly impacting the kingdom of Thor and destroying it completely, also causing horrendous damage to Odin and Fenrir, plunging the world back into a medieval state.
Tales of Phantasia
With no memories of the three kingdoms of old, the people of Aselia were left to rediscover magitechnology on their own. New settlements were built and eventually new countries were formed, with the two most powerful cities in the world becoming Alvanista and Midgards. At around 4200 on the Aselian calendar, the city of Midgards began investigating magitechnology following the discovery of the ruins of Thor. However, because of this, they were attacked by a man named Dhaos who destroyed them all with his army of monsters. Later, their information on magitechnology was taken by the world's other cities and used to build machines of their own. The city of Euclid benefited greatly from these designs and soon grew to become as great a power as Midgards once was.