story.
In the exciting new season of Bakugan, the VESTROIAN star system is made up of six planets each home to a different species of Bakugan. Experimental weaponry causes the Bakugan to be transported to Earth, where humans welcome them, until teenagers start pairing with Bakugan and gain the ability to grow to giant size; during this time filled with fear, the Catastrophe takes place. (Source: 9Go!)
