Gaia is referred to as the "spirit of the Earth" in Final Fantasy: The Spirits Within. It is the central component in the Gaia Theory propagated by Dr. Sid and his wife, but was regarded as fairytale by others, including General Hein.
The Earth Gaia was finally proven to exist when Aki and a colleague, General Gray Edwards fell in a crevice near the Leonid Meteor impact site, when both were searching for the eighth and final Spirit to complete the wave pattern that can erase the Phantoms from existence. The Earth Gaia was shown as an amorphous blue sea, similar to the color of the spiritual energy, or souls that are extracted whenever a living thing is in contact with the Phantoms.
The Alien Gaia is in essence similar to Earth's Gaia in that it is, or was, the spirit of its planet and all of its planet's spirits are connected to it. Shown as enormous red creeping vines, similar to the nature of the Phantoms, the Alien Gaia is hostile to its current environment and all living things become victim to the hatred carried by it.
Gaia was the goddess or personification of Earth in ancient Greek religion, one of the Greek primordial deities. Gaia was the mother of all: the heavenly gods, the Titans and the Giants were born from her union with Uranus (the sky), while the sea-gods were born from her union with Pontus (the sea). The Greek word "γαῖα" (transliterated as gaia or gaea) is a collateral form of "γῆ" meaning Earth. Her equivalent in the Roman pantheon was named Gaea (Terra in more ancient documents). This is alluded to in Final Fantasy IX with the existence of Gaia's twin world.
The mythological name Gaia was revived in 1979 by James Lovelock, whose Gaia hypothesis proposes that living organisms and inorganic material are part of a dynamic system that shapes the Earth's biosphere, and maintains the Earth as a fit environment for life. In some Gaia theory approaches the Earth itself is viewed as an organism with self-regulatory functions. This theory is especially alluded to in Final Fantasy: The Spirits Within's take on Gaia as the planet's soul.
The concept of Gaia in Final Fantasy: Spirits Within resembles the Gaia hypothesis that proposes that living organisms and inorganic material are part of a dynamic system that maintains the Earth as a fit environment for life.
- The concept of Gaia is similar to the Lifestream of Final Fantasy VII. Dr. Sid's Gaia Theory also mirrors the elements of the game's Lifestream and Spirit Energy. The story is written by Hironobu Sakaguchi, and thus it is understandable that there are parallels to the series. Additionally, the world of Final Fantasy VII, known in-game as the Planet, is officially called Gaia.
- Similar concepts of a planet's soul or life energy has also been seen in Final Fantasy IX, where the main planet where the game takes place is also called Gaia.