Gaia (The Spirits Within)

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 Gaia Theory
A theory created by Dr. Sid and his wife, the Gaia Theory claims that every living thing has a spirit. This theory was shared with other scientists, but it was unpopular as there was no evidence that such entity existed. Dr. Sid and his wife kept it to themselves, until the scientist lost his wife in a Phantom invasion over Toronto.

The theory was then shared with Aki Ross and was then made known to the ruling Council as a hypothesis. General Hein became the greatest adversary to the theory, demanding evidence for Dr. Sid's claims. A few members of the Council, however, allowed Dr. Sid time to prove this theory when Aki Ross revealed that her body had successfully contained a Phantom spirit inside her.

Earth Gaia
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 eight 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.

Alien Gaia
The Alien Gaia was instead shown as red creeping vines, similar to the nature of the Phantoms and other Phantom-like entities whose anatomy is partly made up of long, creeping tentacles. Like the Phantoms, the Alien Gaia is hostile to its current environment and all living things became victim to the hatred carried by the Phantoms.