Unsuspecting inhabitants of the planet Earth are going about their business, enjoying a bright and particularly beautiful sunny day, when a young Japanese boy spots a shiny object falling from the sky... Has an alien invasion finally begun?
Elsewhere in Japan, Keroro, frog sergeant and leader of the Space Invasion Army Special Tactics Platoon of the 58th Planet in the Gamma Planetary System, has discovered the perfect hideout. He infiltrates the home of the Hinata family in an attempt to establish a headquarters that he and his troops could use to prepare for world domination... but earthlings Fuyuki and Natsumi Hinata are too much for him to handle! Natsumi instinctively calls them out of hiding, leaving the hapless sergeant no option but to reveal his secret identity. The two siblings soon welcome the sergeant to their home, all thanks to Fuyuki's generos—err... curiosity.
The Sergeant has successfully infiltrated his first target area! Or has he? Join Keroro Gunsou in his dastardly attempt to take over the world!