Sgt. Frog Episode 199: Kururu, Kururun Idol Legend / Keroro, Resetting My Mind!
Episode 199 of 358 of Sgt. Frog, aired February 16, 2008, 25 minutes. Available with English subtitles and dub where released.
Episode summary
Kululu becomes a really popular idol. He takes advantage of it to be even more of a jerk than ever. And then Keroro decides the platoon needs to return to their roots as invaders... by acting like stereotype villains, complete with costume changes! Source: crunchyroll