Phantom (The Spirits Within)

Phantoms in the movie Final Fantasy: The Spirits Within are initially depicted as alien invaders. Arriving on Earth on a large chunk of meteorite, the Phantoms invaded with little to no resistance. Every living thing touched by a Phantom will have its life and soul consumed. Phantoms come in many forms; though the invaders are mostly humanoid, there are also large insect-like and fish-like Phantoms.

A discovery was made that Phantoms could not enter through certain electromagnetic fields. To repel the invasion, Earth scientists proposed the creation of barrier cities; cities enveloped in EM fields. Due to the invasion, barrier cities are mostly concentrated on the city center. Phantoms are left to wander the entire Earth.

Eventually, Aki Ross discovered from her dreams after being infected by a Phantom, that the Phantoms are actually spirits or ghosts of aliens from another planet. A cataclysmic weapon unleashed in the midst of the civil war on the alien planet wiped out its entire population. The aliens carried on their hatred even until death, which explains why most Phantoms are hostile. The meteorite from which they arrive is actually a chunk from the alien planet, which carried with it the alien ghosts and the ghost of the alien "Gaia". At the end, the spirits Aki found and the Phantoms cancel out each other, erasing all existence of Phantoms from the planet.