"Aria the Benedizione" is a continuation of the "Aria" series, set in the picturesque, water-filled city of Neo-Venezia on the planet Aqua, a terraformed Mars. The story centers on the daily lives and experiences of the undines, gondoliers who guide tourists through the city's canals. The narrative focuses on Akari Mizunashi, a cheerful and optimistic apprentice undine working for the Aria Company, alongside her mentor Alicia Florence and fellow apprentices Aika S. Granzchesta and Alice Carroll from rival companies.

The film explores themes of growth, friendship, and the passage of time, as Akari and her friends navigate their roles as undines and their personal journeys. A significant portion of the story revolves around Alicia's impending retirement, a pivotal moment that forces Akari to confront the inevitability of change and the importance of cherishing fleeting moments. The narrative is deeply introspective, emphasizing the beauty of everyday life and the connections formed between people.

Key characters include Akari, whose boundless enthusiasm and love for Neo-Venezia drive much of the story's warmth; Alicia, whose grace and wisdom serve as a guiding light for Akari; Aika, the spirited and sometimes brash apprentice from Himeya Company; and Alice, the reserved yet talented undine from Orange Planet. Their interactions and shared experiences highlight the camaraderie and mutual support that define their relationships.

The plot is episodic, with a focus on small, meaningful moments rather than a grand overarching conflict. Scenes often depict the undines guiding tourists, participating in festivals, or simply enjoying the serene beauty of Neo-Venezia. These moments are interwoven with reflections on personal growth and the bittersweet nature of transitions, culminating in a heartfelt exploration of Alicia's legacy and Akari's readiness to step into a more independent role.

"Aria the Benedizione" maintains the series' signature tranquil and reflective tone, offering a poignant conclusion to the themes of mentorship and the passage of time that have been central to the franchise. The film serves as both a celebration of the characters' journeys and a meditation on the enduring beauty of life's simple pleasures.