Three weeks after the incident that left Captain Napolipolita's ship balancing on top of Graviton City, A-Ko and the gang go on summer vacation. While A-Ko ponders losing some weight and B-Ko devises another plan to defeat her redheaded rival to win C-Ko, Napolipolita and Spy-D experience severe homesickness - begging for a way to return to their home planet. Meanwhile, Hikari Daitokuji - B-Ko's father and the CEO of the Daitokuji Financial Group - arms the local military with new mecha to attack Napolipolita's ship and obtain its advanced technology.
