Episode 313
Keroro's mother receives a letter from him that wildly exaggerates how close they are to finishing invading, so she shows up on Earth to "help." Then, on Mothers' Day, Aki decides to join the Keroro Platoon and become an invader for the day! Source: crunchyroll
Aired 08/05/2010EP 313 - Episode 313
Sgt. Frog
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. 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.
(Source: Anime News Network)