"Aqua" is a two-volume manga series that serves as a prequel to "Aria," both created by Kozue Amano. Set in the early 24th century, the story takes place on a terraformed Mars, now called Aqua, where much of the planet is covered in water. The narrative centers around Akari Mizunashi, a young girl who moves from Manhome (Earth) to the city of Neo-Venezia, a replica of Venice, to pursue her dream of becoming an Undine—a gondolier who guides tourists through the city’s canals.

Akari joins the Aria Company, one of the three major gondola companies in Neo-Venezia, and begins her training under the guidance of Alicia Florence, a skilled and kind-hearted Undine known as one of the "Three Water Fairies." The series explores Akari’s daily life as she learns the ropes of her new profession, navigates the challenges of adapting to a new environment, and forms bonds with the people around her. Her interactions with Alicia, as well as her fellow trainees Aika Granzchesta from the Himeya Company and Alice Carroll from the Orange Planet, form the core of the story.

The narrative is episodic, focusing on small, slice-of-life moments that highlight the beauty and tranquility of Aqua. Akari’s experiences range from mundane tasks like learning to row a gondola to more whimsical encounters, such as discovering the unique traditions and legends of Neo-Venezia. The series emphasizes themes of friendship, personal growth, and the appreciation of life’s simple pleasures, all set against the serene and picturesque backdrop of a water-filled world.

Through its gentle pacing and focus on character interactions, "Aqua" establishes the foundation for the world and relationships that are further developed in "Aria." The series captures the charm of Neo-Venezia and the quiet determination of its protagonist, offering a heartfelt introduction to the universe that continues to unfold in its sequel.