In the year 2301, Aqua, a once dry planet now transformed by terraforming into a watery paradise, is home to Neo-Venezia, a stunning replica of Venice from Earth. Visitors and locals alike revel in the city's beauty, gliding through its canals on gondolas as skilled women called Undines guide them. Akari Mizunashi, a young girl from Earth, sets out to fulfill her dream of becoming an Undine by apprenticing at Aria Company in Neo-Venezia. Alongside her mentor Alicia, a quirky cat named Aria, and fellow apprentice Aika, Akari navigates the challenges of training while immersing herself in the enchanting wonders of the city.