"Keroro Gunsō: KeroZero Shuppatsu da yo! Zen'in Shūgō!" is a direct-to-video anime special that serves as a continuation of the popular "Keroro Gunsō" (Sgt. Frog) series. The story revolves around the Keroro Platoon, a group of frog-like alien invaders from the planet Keron, who have been stranded on Earth. Led by Sergeant Keroro, the platoon includes the hot-headed Private Second Class Tamama, the tech-savvy Corporal Giroro, the enigmatic Lance Corporal Dororo, and the eccentric Sergeant Major Kururu. Despite their initial mission to conquer Earth, the platoon has largely abandoned their invasion plans, instead integrating into human life and forming bonds with the Hinata family, particularly with siblings Fuyuki and Natsumi.

The narrative begins with the Keroro Platoon receiving a mysterious message from their home planet, Keron, instructing them to return immediately. The message is cryptic, and the platoon is unsure of the reason for the recall. Despite their reluctance to leave Earth, they prepare for departure, reflecting on their time spent with the Hinata family and the friendships they have formed. However, as they prepare to leave, a new threat emerges: a rogue Keronian faction known as the KeroZero, led by a shadowy figure with a personal vendetta against the Keroro Platoon. This faction seeks to exploit Earth's resources and destroy the planet, putting both the platoon and their human friends in danger.

The Keroro Platoon must now confront the KeroZero faction while grappling with their own feelings about leaving Earth. The story explores themes of loyalty, friendship, and the complexities of identity as the platoon questions their roles as invaders versus their attachment to their adopted home. The Hinata siblings play a crucial role in supporting the platoon, with Fuyuki's optimism and Natsumi's determination providing emotional grounding. The narrative builds toward a climactic battle where the Keroro Platoon must use their unique skills and teamwork to protect Earth and their newfound relationships.

Throughout the special, the series maintains its signature blend of humor, action, and heartfelt moments. The interactions between the platoon members and the humans highlight the growth of their bonds, while the introduction of the KeroZero faction adds a layer of tension and stakes to the story. The special concludes with a resolution that reaffirms the platoon's commitment to Earth and their human friends, leaving the door open for future adventures.