Final Fantasy: The Spirits Within

Gaia is the life force of the planet that gives creatures on the planet life. Every living creature has this spirit inside it, including humans. The researchers discover the 7th spirit is any phantom spirit that comes in contact with Gaia. Therefore, the phantom virus within Aki automatically becomes the final spirit since it is already in direct contact with her spirit, and the wave is complete. Gray sacrafices himself in order to transmit the completed wave into the alien life-stream, which eliminates the phantoms, and saves the world.