Sgt. Frog Episode 10: Sgt. Frog Versus the Cavitians of Cavity 9!
Episode 10 of 358 of Sgt. Frog, aired June 5, 2004, 25 minutes. Available with English subtitles and dub where released.
Episode summary
Keroro has a cavity and it is up to the platoon and the Hinatas to battle the enemy invaders in his mouth with Kururu's invention, with a slight parody of Gundam.