its an old 3D animation movie(like pixar’s movies, actually not sure) just with a more anime kinda style.

the story starts with the main hero going to some event and then an alien invasion starts and after that we have a time skip and we see that humans now live underground. the main hero decides to take his girlfriend up the surface or something and his girlfriend gets killed.

after that he join the army and we see a scene where he fight and faints and and wakes up in this power rangers looking headquarters where he gets a robot and meets other people with robots.

i remeber that after that there was a fight in the desert and that the final fight was in this icy place?

thank you  very much.