Hold up a second! Are you looking for the game that this story takes place in? Find it here!
This page is for the Story Mode of Battle of the Universes, entitled "War of the Worlds".
Chapter 1: "The Great Airship Armada"
It's the Worldly Comet Festival in the Mushroom Kingdom where Mario and Luigi are celebrating. Suddenly, a portal opens up, not only bringing out Bowser's airships but also Numbuh 1! The brothers rush to fight through the enemies, but are taken down by them.