In the year 2004, a five-member alien invasion force lead by Sgt. Keroro of the planet Keron should have taken over Earth. However, a human science-fiction fan named Fuyuki foils this plan when he has a nightmare of an alien invasion and wants to stay in bed. In an attempt to get his brother out of bed, his sister Natumi shouts that she sees an alien. At that moment, the wallpaper disguise fails and the Hinata family sees Sgt. Keroro. Now Keroro must reunite with his four lost members, take over the Earth, remain friends with Fuyuki, do the housework, and build Gundam models without getting caught by Earth authorities who might want to dissect him.