"Ar Tonelico" is an anime series based on the video game series of the same name, set in a world where humanity resides on floating continents due to the devastation of the planet's surface. The story revolves around the coexistence of humans and Reyvateils, a race of artificial beings capable of harnessing the power of song to manipulate the environment and perform advanced technological feats. The narrative primarily unfolds on the floating continent of Sol Ciel, where the Tower of Ar Tonelico, a massive structure housing the Reyvateils, serves as the central hub of civilization.

The protagonist, Lyner Barsett, is a young knight tasked with protecting the Reyvateils and maintaining the balance of their world. Lyner's journey begins when he is sent on a mission to investigate disturbances in the Tower, which threaten the stability of Sol Ciel. Along the way, he encounters Aurica Nestmile and Misha Arsellec Lune, two Reyvateils with contrasting personalities and abilities. Aurica is gentle and reserved, while Misha is bold and outspoken. Both Reyvateils play crucial roles in the story, as their songs are essential to maintaining the Tower's functions and combating the growing threats to their world.

As Lyner delves deeper into the mysteries of the Tower, he uncovers a conspiracy involving the misuse of Reyvateil technology and the emergence of a rogue faction seeking to exploit their power. The narrative explores themes of coexistence, the ethical implications of advanced technology, and the struggle to preserve a fragile world. The characters face moral dilemmas, personal growth, and the consequences of their actions as they work together to protect their home.

The series also introduces secondary characters, such as Radolf Schnaizen, Lyner's mentor, and Jack Hamilton, a scientist with a vested interest in Reyvateil research. These characters contribute to the overarching plot, providing additional layers of conflict and resolution. The story builds toward a climactic confrontation that tests the bonds between humans and Reyvateils, ultimately determining the fate of Sol Ciel and the Tower of Ar Tonelico. The anime blends elements of fantasy, science fiction, and drama, creating a narrative that emphasizes the importance of unity and the power of song in shaping the destiny of their world.