Hametsu no Mars

Some time after a space mission to Mars ends in destruction, strange monsters called "Ancients" begin appearing around Tokyo. A group of specialists consisting of three girls and one troubled young boy must fight the Ancients until they can come to understand exactly what it is they are fighting. When one of the Ancients tells them that they are the true invaders of Earth, they must search within themselves to grasp what truly is reality.

(Source: Anime News Network)