Chibi Kero: Kerobouru no Himitsu!?
English name: Chibi Kero: Secret of the Kero Ball!?
Genres: Comedy
Type: Special, Episodes: 1
Aired: Mar 17, 2007
Studio: Sunrise
Source: Unknown
Rating: G - All Ages
Synopsis:
A young Keroro tries to impress Pururu by showing off the Kero Ball, a ball borrowed by Giroro from his brother Garuru. While testing the buttons, he accidentally transports the 4 tadpoles inside the ball. To get out, they must win the pinball maze. In the outside world, a young blue tadpole Kururu picks up the ball and hears the cries of help. He makes a deal to free those trapped inside if he gets a plate of curry rice. A deal is a deal and with the Kero Ball, a plate of curry rice is produced for Kururu. Unfortunately, the plate grows bigger and bigger and bigger. It got so big, that Kururu was immersed in the curry. The yellow curry slowly transforms the blue Kururu into the "yellow devil" and as the film is about to fade into black, "Kukuku" is heard.

(Summary found on Veoh.com)