"Keroro Gunsō," also known as "Sgt. Frog," centers on the misadventures of Keroro, a bumbling yet ambitious frog-like alien from the planet Keron. Keroro is part of an invasion force sent to conquer Earth, but his plans are derailed when he is discovered by the Hinata siblings, Natsumi and Fuyuki. Instead of carrying out his mission, Keroro becomes a houseguest in the Hinata household, where he is forced to perform chores in exchange for shelter. Over time, Keroro forms an unlikely bond with the family, complicating his original objective.

Keroro is joined by four other members of the Keron Platoon: Giroro, a militaristic and disciplined soldier; Tamama, a hyperactive and emotionally volatile recruit; Kururu, a mischievous and brilliant inventor; and Dororo, a stealthy and pacifistic ninja. Each member of the platoon has distinct personality traits and motivations, often leading to humorous and chaotic situations. Despite their initial goal of conquering Earth, the platoon frequently becomes distracted by mundane human activities, such as video games, manga, and pop culture, which they find endlessly fascinating.

The series blends episodic comedy with occasional overarching storylines. Many episodes focus on the platoon’s comedic attempts to carry out their invasion plans, which are invariably thwarted by their own incompetence, the Hinata family’s interference, or the intervention of other characters, such as Aki Hinata, the siblings’ mother, who is a powerful and mysterious figure. Other recurring characters include Angol Mois, a kind-hearted alien princess with destructive powers, and Nishizawa, a classmate of Natsumi and Fuyuki who harbors a crush on Natsumi.

As the series progresses, the Keron Platoon’s relationship with the Hinata family and the people of Earth deepens, leading to moments of genuine camaraderie and emotional growth. While the invasion plot remains a recurring theme, it often takes a backseat to the platoon’s comedic exploits and their gradual integration into human society. The series explores themes of friendship, cultural exchange, and the absurdity of war, all while maintaining a lighthearted and humorous tone.