From publisher blurb:
The “Big Book of Kaiju” is many things. It’s a collection of giant monsters culled from the annuls of movie history. Any fan of the genre will be able to recognize a favorite monster here. It is also a game master aid for the “Mecha vs. Kaiju” game, powered by Fate Core, offering statblocks for adversaries to throw against players. And finally it is an aid to players of “Mecha vs. Kaiju,” giving them an insiders look at how citizens of Japan and the world view the creatures that daily menace their lives.
If you play other Fate games it is unnecessary to have the Mecha vs Kaiju Core Book to use this supplement. Each kaiju is fully stated out with unique stunts and is usable in any Fate game. However, if you want your players to have a chance of beating any but the weakest version of these monsters, it's best to have a mecha at your side!