Kero 0: Shuppatsu da yo! Zenin Shuugou!

Synopsis

This episode serves as a prequel to the main Keroro Gunsou series, designated as episode 0. KeroZero premiered in theaters alongside Keroro Gunsou Movie 4. On the day the Keroro battalion was set to depart from Keron Planet for Planet Earth, an alien enemy force attacks the Keron space station, where Giroro and Zeroro (who would later be known as Dororo) await Keroro's arrival.