When strange crystals fall from the sky and start making the monsters of the world behave differently, the Global Defense Force (GDF) is convinced it is another invasion attempt from the Vortaak. Meanwhile on Monster Island, Godzilla feels an urge to break out and destroy these strange power crystals before too much damage is done. That's the setup and story behind
Godzilla Unleashed, but then again, stories in fighting games, especially brawlers like this one, are little more than fanfare and an excuse to string together fights.
As you progress through the story, you will have locations from around the world open up to you. You will fight everywhere from Tokyo to New York and even the crashed Vortaak Mother Ship. While each location looks different, they are basically the same. Sure Monster Island has more mountains that you will have to walk around and the Vortaak Mother Ship has an alien design, but they tend to blend together in my mind.
Most missions involve either stopping all of the enemy monsters or destroying all of the larger power crystals (the smaller ones regenerate and act as health or energy boosters for the fighters). I found it interesting how the game handles friends and foes in that in general, monsters of the same faction as you won't attack you while the others might have a shaky alliance with you depending on how you feel about the power crystals.
The monsters in the game are divided into four factions, Earth Defenders (Godzilla, Mothra, Baragon), GDF (Kiryu, Jet Jaguar, Mecha-King Ghidorah), Aliens (Gigan, Orga, Megalon) and Mutants (Desteroyah, Obsidius) and while the Mutants and Aliens tend to want to keep the crystals around, the other two factions are against them. One of the aspects of this game that I found really difficult was keeping track of just who was on my side and who wasn't while actually in the fight. I can't claim to be the biggest Godzilla fan, so I can't name each of the monsters and their affiliations off the top of my head. So because there was no visual friend or foe indicator in the game, I often found myself attacking a friend and turning him into a foe (not good).