Gaia

Overview
Gaia (or Gaea), is the name for the plane in which most of the events of the As The Last Leaf Falls series, among many others, occur. Unkbeknownst to many, Gaia is not simply a planet but a primordial: a sentient, ageless being of planetary proportions. Gaia has a rather curious disposition for a primordial, often manifesting in a physical form from time to time to observe humans.

Despite being ageless, Gaia has been depicted in many stories to be in a state of slow decay, mostly as a result of humanity's actions.

Gaia's Early Days
Legends and speculations on the prehistory of Gaia often depict it as a "place filled with goodness"; a primordial unique in that no demons merged with it, making it a planet filled only with positive concepts. This was partly true in that the demons who were supposed to exist were locked away by the first human kingdom, Utopia, in an artifact known only as the Book. The event, known as the Fall of Utopia, occured when the queen Pandora, accidentally released the demons from the Book, filling the world with evil. This event has been mostly considered to be the first catalyst of Gaia's slow "death".

The War of Gods
A long period of chaos and unrest spread throughout Gaia after the Fall. Of what little accounts remain from that time, the planet became a colossal battlefield, as the newly awakened demons now clashed with the deities for the planet's supremacy. Eventually, the war ended in the deities'  favor, ridding most of the demons' corporeal forms, but not without terraforming Gaia, among other lasting damages, turning the planet into what it is at present.

Age of Legends
An age marked by adventures and myths with spirits, monsters and the like, hence the name. Many races, mythical and otherwise flourished during this period, as well as magic. Many religious orders and writings trace their origins from this time.

Age of Magic
A period that started with the establishment and domination of sorcerer guilds, this age was the start of human civilization's rise to power. At the time, humans were becoming increasingly curious about the world and turned to widespread exploring and colonization.

This age also saw a decline in the mythical races, both natural and intentional, as the wild places of the world steadily became human lands.

The Akasha Incident
An event which saw Akasha- a mortal embodiment of Destruction- challenging the gods to bring about a new reality by ripping open the Fabric of Concepts and changing it from within. While total annihilation was ultimately avoided, Akasha's attempt caused great and permanent damage to Gaia, its deities, and even the Universe as a whole.

This event, though engineered by a human, was believed to be of Destruction's will, and a sign of its inevitable return.

Age of Man
The world underwent significant changes in the aftermath of the Akasha Incident. For one, mythical races, most of which were already considered extremely rare, were seen in much less frequency. The presence of magic sharply declined, as more and more people lost the ability to use and feel it in their surroundings. Even the deities have distanced themselves from worldly affairs, leaving humanity in a world reeling from near destruction. This age, aptly named after man, was a huge crossroads that saw humanity rising up from the ashes, and magic fading into antiquity.

Humanity managed to rebuild and reorganize during this time, though developing what was then a deep, almost paranoid fear of magic. Because of this, the old guilds were quickly replaced with noble heirarchies; a system often overshadowed in the past because of the abundance of magic. The demand for mechanical technology also exploded almost overnight, making what little remained of magical technology obsolete or luxuries reserved only for the select few.

It was in this time that the human kingdoms merged, forming large nations spanning entire seas and continents.

Age of Decline
The ever expanding human civilization on Gaia was not successful without a price. Continuous destruction of nature took its toll on man as it became increasingly harder for them to sustain their high-maintenance lifestyles. Even so, humanity chose to turn a blind eye on what was becoming a serious threat to their existence.

Eventually,  whole ecosystems collapsed, exctinctions were widespread, and none but a few pockets of nature concealed and preserved by Gaia's will remained. The rest of the world were reduced to a barren wasteland, with humanity barely surviving through barricading themselves within enclosed capsule colonies.