ARIA theme. 水星领航员Chrome主题.
本故事的时代背景在24世纪。彼时人类在火星上进行行星地球化改造工程，由于两极冰帽融解的水量超乎预期，全星球有90%被海洋覆盖，因而被人称呼为“水星”（AQUA）。在此星球上有个以过去被称为水都的威尼斯为范本所建造的城市新威尼斯（Neo-Venezia），因其仿古的建筑与承袭传统的生活方式而广受观光客喜爱，而其中有一种驾驶小舟穿梭于运河之间，带领观光客游览整座城市的职业，被称为领航员（Undine）。
出身于地球的水无 灯里，以成为能独当一面的领航员为目标而来到新威尼斯，目前在 艾莉西亚 和 亚利亚社长 的 Aria Company 中见习。身为半熟手的她，每天都持续练习操控贡多拉及观光导览。《水星领航员》一书便是在描写灯里以及她身旁的朋友在一年四季中的日常生活点滴。
Aqua and Aria take place in the early 24th century, starting in 2301 AD, in the city of Neo-Venezia on the planet Aqua—formerly Mars, which was renamed after being terraformed into a habitable planet covered in oceans around 150 years ago.[4] Neo-Venezia, based on Venice in both architecture and atmosphere,[5] is a harbor city of narrow canals instead of streets, traveled by unmotorized gondolas.[6]
At the start of Aqua, a young woman named Akari arrives from Manhome (formerly Earth) to become a trainee gondolier with Aria Company, one of the three most prestigious water-guide companies in the city. Her dream is to become an undine, a gondolier who acts as tour guide (see Terms below). As she trains, Akari befriends her mentor Alicia, trainees and seniors from rival companies - Aika, Alice, Akira and Athena and others characters in the Neo-Venezia city. Aqua covers Akari's arrival on Aqua and her early training as a Pair, or apprentice, while Aria continues her training as a Single, or journeyman, culminating in the graduation of her, Aika, and Alice as full Prima undines.
