It's summer in Graviton City, and the girls all have a break from school! A-Ko decides to lose a few inches, C-Ko makes a list of all the cool things that she'll buy, and B-Ko vows to get A-Ko out of the way once and for all so that she can have C-Ko to herself. To this end, she designs a new giant mecha, better than all the others. But her father steals her designs and uses them to attack the crashed alien spacecraft (now high-class restaurant) in an attempt to steal the advanced technology of the aliens.