"SGT Frog" centers on Keroro, a frog-like alien from the planet Keron who leads the Keroro Platoon, a group of amphibious invaders sent to conquer Earth. However, Keroro’s plans are thwarted when he is discovered by the Hinata siblings, Fuyuki and Natsumi, who take him captive. Instead of continuing his mission, Keroro becomes a houseguest in the Hinata household, where he develops a fascination with Earth’s culture, particularly Gundam models and anime. Over time, his initial goal of invasion is overshadowed by his growing attachment to life on Earth and his reluctance to harm the humans he has come to care for.

The Keroro Platoon consists of five members, each with distinct personalities and roles. Keroro, the self-proclaimed leader, is often lazy and comically inept, more interested in hobbies than conquest. Giroro, the weapons expert, is the most serious and dedicated to the invasion mission, though he harbors a soft spot for Natsumi. Tamama, the youngest and most energetic, has a dual personality that shifts between sweet and explosive. Kururu, the tech-savvy and mischievous inventor, often creates gadgets that backfire or cause chaos. Dororo, the stealth specialist, is a pacifist who struggles with his role in the platoon due to his aversion to violence.

The series blends episodic humor with occasional overarching plotlines, often focusing on the platoon’s failed attempts at invasion or their interactions with the Hinata family and other Earth residents. The Hinata siblings play key roles in the story: Fuyuki, a gentle and curious boy with an interest in the supernatural, and Natsumi, a strong-willed and athletic girl who frequently clashes with Keroro. Their mother, Aki, is largely indifferent to the aliens’ presence, while their father, who rarely appears, remains unaware of the platoon’s existence.

Recurring themes include the clash between duty and personal desires, as the platoon members grapple with their loyalty to Keron and their growing affection for Earth. The series also explores friendship, family dynamics, and the absurdity of everyday life, often through slapstick comedy and parodies of popular culture. Despite their initial mission, the Keroro Platoon’s antics rarely result in genuine harm, and their presence becomes a source of humor and occasional heartwarming moments as they integrate into human society.