"Aria the OVA ~Arietta~" is a self-contained story set in the serene, futuristic city of Neo-Venezia on the planet Aqua, a terraformed Mars. The narrative centers on Akari Mizunashi, a cheerful and optimistic apprentice gondolier, or "Undine," working for the Aria Company. The OVA explores themes of friendship, nostalgia, and personal growth, capturing the essence of the larger "Aria" series.

The story begins with Akari reflecting on her early days as a trainee under her mentor, Alicia Florence, the graceful and talented prima Undine of Aria Company. Through a series of flashbacks, Akari recalls her initial struggles and insecurities as a novice, contrasting them with her current confidence and skill. The narrative shifts between past and present, highlighting Akari's journey and the bond she shares with Alicia. A pivotal moment occurs when Akari discovers an old photograph of Alicia and her former mentor, Aria Company's founder, Grandma. This discovery prompts Akari to reflect on the transient nature of time and the importance of cherishing moments with loved ones.

The OVA also introduces a subplot involving Akari's friends, Aika S. Granzchesta and Alice Carroll, who are apprentices at rival gondola companies. Their interactions provide lighthearted moments and reinforce the camaraderie that defines the series. The story culminates in a poignant scene where Akari and Alicia share a quiet gondola ride, symbolizing the passing of wisdom and the enduring connection between mentor and student.

The main characters are portrayed with depth and consistency. Akari's unwavering optimism and curiosity drive the narrative, while Alicia's calm and nurturing demeanor serves as a guiding force. Aika and Alice add dynamic energy to the story, balancing Akari's introspective moments with humor and camaraderie. The OVA maintains the tranquil, slice-of-life tone of the "Aria" series, emphasizing the beauty of everyday experiences and the importance of human connections.