Keroro, Visitor from the Future / 623, Tragedy of the Radio Star
A robot comes from the future to help Keroro be less of a screw-up... but not in the way you'd expect. It's 623's final radio show, and Natsumi's invited! Can she resist the urge to shatter the mystery? Source: crunchyroll
Aired 05/03/2011EP 354 - Keroro, Visitor from the Future / 623, Tragedy of the Radio Star
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)