The plot of the movie tells about War of mankind with alien guests. People always considered that newcomers will arrive from far galaxies, but they came to us from sea depths. In the Pacific Ocean the portal which connects our planet with another dimension opened. Newcomers came to people not with good intentions, and with the purpose to seize the planet.
They thought that a lot of time for this purpose isn't required, but people didn't give up and showed them worthy resistance. War which would will seemed very short, dragged on for many years. This opposition claimed with itself a set of the lives and settled practically all resources. However people could create huge robots by means of which they continue fight with alien monsters кайдзю . Forever to stop this War and to get rid of newcomers, people need to destroy a portal, and it is a difficult task.