In the near future a dimensional rift has opened near the floor of the Pacific Ocean and from it emerge gigantic, Godzilla-sized monsters that want to destroy mankind. In response, the human race comes together to create giant robots to battle them. They are operated by two humans, since the technology that enables them to operate the machines takes two brains, one for the right side, one for the left side. Often, it's relatives who pilot, such as two brothers or a father and son, since their brains are similar.
The main character is Raleigh Becket, who loses his brother in one of the battles with a particularly ferocious creature. He survives, but chooses to spend the next five years in obscurity, working on a massive wall in Alaska. Now, the robot program is being discontinued and in place a series of giant walls are being constructed around major cities, to keep out the monsters. Of course, they don't work.The attacks keep getting worse--and one scientist manages to meld his mind with one of the brains of the creatures--and discovers what the reason for the invasion is.
This is one of the best giant monster movies ever made--it's like a realistic version of Ultraman or Johnny Sokko and his Flying Robot. Highly recommended.