No biggie,so they proceed to the impact point but lo and behold, the enemy is there too and they still wanna fight (BTW, that's the battle you see in the intro). So the moon comes mighty close, and BLAM! it opens up like a puzzle box because its actually the prison of Bahamut! (the dragon racking a major kill count in the intro) The old dude tries to save the army, but it doesn't really work and a lot of em get fried. So now, the old dude tries to seal the free dragon (That's the whole pillars of light routine in the intro movie), but apparently Bahamut has better magic resistance than he thought, and the spell fails.

With no tank to take aggro, Bahamut gets pissed at the mage dude and starts charging its ultimate. Seeing this, the old dude knows the raid is going to wipe, so he casts a shield on the main heroes to freeze them save and sound in time. After a time, the heroes unfreeze and join in on the rebuilding effort with the remaining survivors.

Thats the story in a nutshell.