Akari Mizunashi, at the age of 15, has left everything behind to travel to Aqua, a sparkling planet covered in water. More than anything, Akari wants to be an "undine" - a female gondolier who navigates the canals of the Aquan city of Neo-Venezia. As she begins her training with the prestigious Aria Company, will she be up to the challenges that await her on the path to achieve her dream?

Winter has come - the mornings are crisp and cold, and it's hard to get out from under the covers to go practice sculling. So as a special treat, Alicia suggests that they visit a hot spring! Akari's never seen one before so she's excited to go, and all the others decide to join in as well.

It's time to ring in the new year, and everyone in Neo-Venezia has come together to celebrate! Even little Ai has come back from Manhome to take part in the winter festival. But as people gather and memories are shared, President Aria suddenly wanders off. Akari and Ai attempt to track him down, but what they find is a mysterious New Year's gift from Aqua itself.

In the still of the night, Akari is woken up by the distant sound of a train. But Neo-Venezia's trains don't run at that hour, so what was it she heard? And to make matters even more mysterious, the next day, President Aria gifts her with a train ticket. It would seem Akari is about to have another brush with the secretive spirit, Cait Sith...