"Aria the Avvenire" is a three-episode OVA series that serves as a continuation and epilogue to the "Aria" franchise, which includes "Aria the Animation," "Aria the Natural," and "Aria the Origination." Set in the futuristic, water-covered world of Neo-Venezia on the planet Aqua, the story revisits the lives of the undines, young women who work as gondoliers and tour guides, showcasing their growth and the bonds they share.

The narrative unfolds through the perspective of Akari Mizunashi, a cheerful and optimistic undine working for the Aria Company. Alongside her friends and fellow undines, Aika Granzchesta of Himeya Company and Alice Carroll of Orange Planet, Akari reflects on their journey from apprentices to full-fledged Prima undines. The series interweaves past memories with present moments, highlighting pivotal events that shaped their careers and friendships. Key flashbacks include Akari's early days as a trainee under her mentor Alicia Florence, Aika's struggles to live up to her family's legacy, and Alice's gradual opening up to others despite her reserved nature.

The central theme of "Aria the Avvenire" revolves around the passage of time and the enduring connections between people. Each episode explores the characters' growth, not only as undines but as individuals who have learned to appreciate the beauty of their world and the people around them. The series also introduces a new character, Ai, a young girl from Manhome (Earth), who represents the next generation of undines and symbolizes the continuation of the legacy that Akari and her friends have built.

The OVA maintains the franchise's signature tranquil and heartwarming tone, emphasizing the serene beauty of Neo-Venezia and the gentle, slice-of-life moments that define the characters' lives. Through its focus on nostalgia, friendship, and the cyclical nature of life, "Aria the Avvenire" provides a fitting conclusion to the "Aria" series while celebrating the enduring spirit of its characters and their world.