April 3rd, 2301. After 150 years of terraforming, planet Mars has become very aquatic, with water covering over 90% of its surface area, hence it has been renamed to "Aqua." A young girl named Akari Mizunashi arrives the Aquarian city of Neo-Venezia, an exact replica of the old Italian city of Venezia (Venice), hoping to become an Undine, female gondolier and tour guide. After landing her job as an intern at Aria Company, she works hard to sharpen her skills, makes new friends, and tries to adapt the laid-back lifestyle at Aqua.