One-hundred and fifty years in the future, terraforming on Mars has caused its polar ice caps to melt, covering 90 percent of the planet's surface with water and making it habitable for humans. Mars is now referred to as Aqua, the water planet. Enter Akari, who leaves Earth for Aqua to become a gondolier, known on Aqua as an undine. Aria Volume 4 continues following Akari on her adventures as she learns about the many facets that make Neo-Venezia such a unique and wondrous place.
