Short episode entitled "Sono Futatabi Deaeru Kiseki ni...", which can be also considered as "Aria the Natural" episode 0.

On the planet Aqua, a world once known as Mars, Akari Mizunashi has just made her home in the town of Neo-Venezia, a futuristic imitation of the ancient city of Venice. In pursuit of her dream to become an Undine — a gondolier who leads high-end tours around the city — Akari joins as a trainee with the Aria Company, one of the three most prestigious water-guide companies in Neo-Venezia. There, she explores the beauty of the city and the world along with other trainees from Aria and rival companies, working hard for her dreams and making new friends along the way.
 
(Source: Tokyopop)
 
Note: Chapter count includes 7 extra chapters.

Akari Mizunashi continues her training to become a Prima Undine (a professional tour guide gondolier) along with her friends Aika and Alice in the peaceful city of Neo Venezia. Despite the fact that these three girls are from competing companies, they are constantly together, learning more about how to become better tour guides and more about the mysteries of Neo Venezia. 
As the group continues to meet interesting and unforgettable people through their daily routines, they will also come closer to the secrets that make the enigmatic and ever beautiful city of Neo Venezia so warm and alive. 
Welcome back to Neo Venezia: the city where miracles can be created by hand.

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