Keroro Gunso is the story of an alien frog commando team stranded on Earth when their invasion force abruptly abandons them. The 4-'men' platoon is headed by Sergeant Keroro ("keroro” is onomotopaeic, considered in Japan to be a sound made by a frog), who is taken in by the very family whose house he attempts to invade.
The show, divided into fifteen-minute episodes, follows Sgt. Keroro’s attempts to take over Earth while building Gundam models in his spare time. Hilarious puns, jokes and spoofs of other animes pepper Keroro Gunso, along with funny and touching storylines and characters.
The manga series by Yoshigiki Mine ran in Monthly Shounen Ace starting in 1999, and has since then been licensed for north american distribution and published by Tokyopop as Sgt. Frog, however, the anime (which is still ongoing on TV-Tokyo and is directed by Junichi Sato of Sailormoon fame) has not been picked up.
The storyline is basically kept simple, like I said before, Keroro is a frog-like alien sent from his home planet on a mission to conquer Earth. But when his cover is blown, his battalion abandons him and he ends up in the home of the Hinata family. Also, while there, he's forced to do household chores and sleep in a dark basement that was once supposedly a prison cell haunted by the ghost of an innocent girl. He even spends his free time assembling Gundam model kits. During his stay, Keroro meets up with subordinates who were also stranded during their failed invasion.