Chibi Kero: Secret of the Kero Ball

One day, Giroro goes to see Keroro and brings his brother’s powerful Kero Ball with him. With the arrival of Zeroro and Pururu, the group is complete; but as the enthusiastic green alien attempts to impress the girlish Pururu with the Keronian weapon, something goes awry and the quartet end up trapped within the Kero Ball! Now if the young gang wants to escape, they must endure a bizarre and hellish arcade-style army training...