World Establishment (development materials) – p. 40 of the FFIX Ultimania

And here is some very fascinating information from the FFIX Ultimania, translated by curiousACfan. Here is the “World Establishment” section, which outlines some of the finer points of the worlds of Terra and Gaia in FFIX.

Gaia
The world that serves as the stage for FFIX. In its civilization, machines are becoming more dominant than magic. Its civilization is young — covering only a portion of the planet’s surface.

Terra
A world with a highly advanced magical civilization. Terra’s people made use of the ultimate magical art, Fusion, in order to attain eternal life. In modern times, Garland watches over the people of Terra until the Fusion process ends and the day comes that they awaken once more.

Fusion
Fusion is cast when the crystal of the world of Terra’s people becomes old. They seek out young planets whose cores have not yet grown through receiving the experiences of living things, assimilating the pure crystals of such young worlds and circulating the power of souls through each person of Terra to finish the process — this is Fusion.

Crystals
At the center of planets, the presence which governs the cycle of souls. Crystals send out souls to be born as living creatures, and when they die, the memories from their lifetimes are sent back to the crystal with their souls. Crystals grow through the accumulation of these memories, and from these complexities, are able to create ever more complex creatures. As crystals grow, their radiance increases and the planet becomes richer. If the circulation should become unable to continue, the accumulation of memory ends, the planet begins to decay, and the crystal itself is returned to the cosmos along with the planet.

Gaia’s crystal has a blue radiance, while Terra’s crystal has a red radiance.

The fusion of Gaia and Terra
Unable to find a young planet with a pure crystal, Garland was driven to the limit and had no choice but to select the young planet Gaia for Fusion. [See Figure 1]

However, Gaia’s crystal was not pure and rejected the process; Gaia’s entire civilization was destroyed in the subsequent cataclysm, and the surface of the world was left in ruin.

The effect of the incomplete Fusion on living creatures and nature was the production of many sub-races, as well as several structures from Terra shifting to the surface of Gaia; as for Terra itself, it was shifted inside of Gaia. Also, because of the incomplete Fusion, Terra’s moon remained and adjusted to Gaia’s original, giving Gaia two moons. (Note: The locations from Terra that ended up on Gaia are Gulug Volcano, the Desert Palace, Ipsen’s Castle, Oeilvert, and, of course, the Iifa Tree.)

The moons receive their crystals’ radiance, which is why Gaia’s moon is blue and Terra’s moon is dyed red. Also, in the sea near Esto Gaza is “the Shimmering Island,” the “interval of both dimensions (Gaia and Terra),” where the radiance of the crystals emanates (for more details on the moons, refer to P.43, “The relationship between the moons and the radiance of the crystals”).

In order to facilitate the recovery of the ruined environment, Garland transplanted Terra’s magical tree Iifa to Gaia. This incident was 5000 years ago.

[Figure 1] Picture from development (Illustration: Hideo Minaba)
Gaia World
•The Shimmering Island (portal entrance) [top arrow]
•Gaia’s moon
•Overlap of both worlds
•Gaia’s crystal [bottom arrow]

The Iifa Tree [the “bridge” in the middle of the diagram]

Terra World
•Overlap of both worlds
•The Shimmering Island (portal exit) [top arrow]
•Terra’s moon
•Terra’s crystal [bottom arrow]