This film begins with humanity working on two separate plans to counter Godzilla. The first is Project "M", and boils down to the 97th iteration of "build a giant robot to fight him".
Specifically, a giant robotic Penguin. Godzilla will never expect that.
Both plans are about to be rendered moot - though it will take the human characters a long, long time to admit that - by the arrival of a new, alien monster. You see, in previous films, some of Godzilla's cells ended up space. There, a scientist character explains to us, they were drawn into a black hole, expelled from a while hole, exposed to intense cosmic radiation, and then fused with a crystalline life-form to form SpaceGodzilla.
Godzilla Movie Scientists: they can come up with flights of fancy like the black hole white hole cosmic radiation crystals malarkey above, but they suck at naming things.
Anyway, SpaceGodzilla looks like a toothier, tuskier version of Big G with massive crystals growing out of his back. He's got all of his earthly counterpart's powers (although his energy blast looks different), and in addition can fly and has a tractor beam. How can such a beast possibly be stopped?
Obviously the answer is "By Godzilla and the Giant Penguin Robot working together", but the movie takes quite a while to get to that point. To be fair, that's because it is working to show that the team-up is necessary. We have to have the scene where SpaceGodzilla defeats Big G, and the scene where it defeats the giant robot, before we can have the scene where the humans (reluctantly) use the robot to help Godzilla.
The battle and destruction sequences of this film are obviously the selling point, and if you're a kaiju fan you'll probably like it. The script is a bit unevenly paced though, and it is sorely lacking in human characters who aren't thoroughly irritating. Check it out only if "guys in monster suits" movies are your thing.