"Chibi Kero" centers around the adventures of Keroro, a diminutive alien frog from the planet Keron, who initially arrives on Earth with the intent to invade it. However, his plans are thwarted when he is discovered by the Hinata family, particularly by the young siblings Fuyuki and Natsumi. Instead of carrying out his mission, Keroro becomes a houseguest of the Hinata family, forming an unlikely bond with them. Over time, Keroro’s priorities shift, and he becomes more invested in Earth’s culture, particularly its hobbies like building Gundam models and indulging in anime and manga.

Keroro is not alone in his mission; he is part of the Keroro Platoon, a group of frog-like alien soldiers. The platoon includes Giroro, a militaristic and serious-minded soldier; Tamama, a cheerful yet volatile recruit with a dual personality; Kururu, a mischievous and highly intelligent inventor; and Dororo, a stealthy and kind-hearted ninja who often feels overlooked. Each member of the platoon has distinct traits and motivations, contributing to the series’ comedic and episodic structure. While they occasionally attempt to revive their invasion plans, their efforts are consistently derailed by their own incompetence, personal interests, or the interference of the Hinata family and other Earth residents.

The series blends humor, science fiction, and slice-of-life elements, often parodying popular anime, manga, and cultural phenomena. Keroro’s interactions with the Hinata family and his platoon members drive much of the narrative, with episodes focusing on their daily misadventures, from failed invasion attempts to mundane activities like household chores or school events. The dynamic between the characters, particularly Keroro’s growing attachment to Earth and its inhabitants, forms the emotional core of the series. Despite its comedic tone, "Chibi Kero" occasionally explores themes of friendship, belonging, and the clash between duty and personal desires, making it a multifaceted and engaging story.