Akari Mizunashi leaves Manhome, the Earth of her time, for Aqua, the terraformed Mars whose city of Neo-Venezia rebuilds Venice with canals and gondolas in place of streets. She apprentices at the small Aria Company under the gondolier Alicia Florence, training to become an Undine, one of the guides who ferry visitors through the waterways. Quiet, unhurried chapters follow her into the city's rhythms alongside the company's mascot cat, President Aria. These two volumes ran under the title Aqua before the story continued as Aria.