The story is about a boy named Mangchi. He is small, but he possesses a magical hammer that helps him get around all his problems. Mangchi lives on a small distant island called Candlestick because everywhere else has turned into a wasteland because of some big catastrophe. When Princess Poplar from the kingdom of Jemius is being pursued by henchmen of the conspirator Moonk, Hammerboy sides with her, ready to unleash all his latent powers in order to save humankind. The movie premiered at the Big Apple Anime Fest on August 30 2003, and went into wide release in South Korea on August 6, 2004.

An original anime advertising Urawa City in Saitama, Japan.

In the land of Ryoza, the neighboring provinces of Shin-Ou and Tai-Kou have been at peace. Queen Shinou is the ruler of Ryoza and her greatest general, Grand Duke Taikou, defends the kingdom with his army of powerful war-lizards known as the "Touda." Although the two regions have enjoyed a long-standing alliance, mounting tensions threaten to spark a fierce civil war. Within Ake, a village in Tai-Kou tasked with raising the Grand Duke's army, lives Erin, a bright girl who spends her days watching the work of her mother Soyon, the village's head Touda doctor. But while under Soyon's care, a disastrous incident befalls the Grand Duke's strongest Touda, and the peace that Erin and her mother had been enjoying vanishes as Soyon is punished severely. In a desperate attempt to save her mother, Erin ends up falling in a river and is swept towards Shin-Ou. Unable to return home, Erin must learn to lead a new life with completely different people, all while hunting for the truth of both beasts and humanity itself, with tensions between the two regions constantly escalating. [Written by MAL Rewrite]