Mysterious giant structures known as Dragon Tails suddenly appear at iconic locations across the globe, from New York to Sydney. The Keroro Platoon, a team of frog-like alien soldiers from the planet Keron on a mission to invade Earth, launches a worldwide investigation. During their research in Paris, the excitable and youngest member, Tamama, vanishes without a trace.

The search leads the rest of the platoon—ambitious Sergeant Keroro, hot-headed Corporal Giroro, eccentric Sergeant Major Kululu, and honorable Lance Corporal Dororo—to the historic island commune of Mont-Saint-Michel in France. There, they encounter a mysterious young girl named Shion, who carries a mystical artifact known as the Dragon Book. Shion possesses a hidden power that can transform others into dragons. One by one, she uses the book to turn Keroro and his comrades into fearsome, powerful dragons.

Shion’s goal is far more dangerous than a simple transformation. She seeks to revive an ancient, colossal creature called the Earth Dragon, a being from prehistoric times. Legend warns that if the Earth Dragon returns, it will absorb all the energy from the planet and fly away, leaving Earth a barren, lifeless husk. While Shion believes this resurrection will serve a greater purpose, the result would be total annihilation. As the Keroro Platoon finds itself transformed into the very monsters that could trigger the apocalypse, Keroro finds himself in an unexpected position: gaining immense draconic power might finally be the key to conquering Earth, but at the cost of destroying the world he has come to enjoy living on. The story follows their struggle against Shion's plan and the awakening of the Earth Dragon, with the help of their human friends Fuyuki and Natsumi Hinata, as they face a worldwide calamity that threatens everything.