A spring wind blows through Neo Venezia. Akari wakes early and notices President Aria missing from the houseboat. She finds him on the roof,staring toward the city. At the Aria Company dock, Akari meets Aika and Alice. They discuss the beginning of the new season and the return of warmer weather. While practicing rowing alone later, Akari spots a small girl crying near a bridge. The girl introduces herself as Azusa. She failed the entrance exam for Orange Planet because the examiners said her height would make it impossible to control a gondola. Akari offers Azusa a ride in her gondola. She shows Azusa how to use leverage and body position rather than height to row effectively. Azusa follows Akari’s movements and successfully propels the gondola a short distance. Akari then takes Azusa to the main canal and points out several short undines working competently. Azusa’s expression changes from despair to determination. She thanks Akari and runs off. Days later, Akari sees Azusa again at the Orange Planet training facility. Azusa has been accepted as a trainee. She explains that she convinced the examiners with a practical demonstration of her rowing. Akari congratulates her. The episode ends with Azusa starting her first lesson while Akari returns to her own practice. The next challenge appears when Aika announces that her promotion exam for Prima Undine is scheduled in one week.

Aika receives a letter from her grandmother,the former owner of the Himeya company, summoning her to the main office in Neo-Venezia. Aika fears her grandmother intends to reprimand her or impose a heavy responsibility. Akari accompanies Aika to the office, and they meet Aika's grandmother, who welcomes them warmly. The grandmother presents a pair of old rowing gloves that belonged to a legendary undine who once taught her. The gloves show signs of long use. She gives the gloves to Aika without further instruction. Aika interprets the gift as a demand to emulate that undine's perfect skill. The grandmother clarifies that she wants Aika to find her own goal, not to copy another, and tells her to discover what she truly wishes to achieve as an undine. Returning to their gondola, Aika reflects on her fear of failure. She decides to stop comparing herself to Akari or Alice and resolves to pursue her Prima examination by focusing on her own pace and strengths. Aika rows back with renewed calm. The Prima examination now stands as her immediate hurdle.

Akari and Alicia prepare breakfast together. Alicia compliments Akari's omelette. Aria社长 shows Akari a newspaper article about the Ca' d'Oro building,scheduled for relocation from Earth to Neo-Venezia the following week. Akari joins Alice at Himeya to study with Aika. The three discuss other relocated structures, including Teatro La Fenice and Cafe Florian. Aika suggests they visit Cafe Florian for tea. On the way, they encounter a young pastry chef selling heart-shaped chocolates in glass bottles at Piazza San Marco. A small boy buys a bottle but trips and shatters it. The chef stops Akari from touching the broken glass and gives the boy a new bottle. Akari purchases two bottles, one for herself and one for Ai. The group proceeds to Cafe Florian, where they enjoy latte and admire the interior paintings. The owner chats with them briefly. As they leave, they notice the pastry chef has vanished from the square. Days later during practice, the three pass the Ca' d'Oro construction site. Akari spots the pastry chef staring at the building before he walks away. Alice observes that he has not sold chocolates for two days. The following day, Akari works a gondola tour with Alicia. While framing a photograph for a tourist, she sees the chef through the viewfinder and notices his stressed expression. After Alicia departs for a gondola association meeting, Akari returns to St. Mark's Square. She follows the chef into Cafe Florian, overhears him praising the paintings, and initiates a conversation. The chef invites her to meet him the next evening. Akari arrives at the agreed time. The chef appears with his stall and thanks her. He explains that he reflected on the broken bottle incident and considered better ways to bring happiness to people. He created new bottles shaped like Neo-Venezia's buildings. The chef asks Akari to select two bottles for herself and Aria社长. They enter Cafe Florian for tea. The owner explains that the cafe's paintings were relocated from Earth before Venice's submersion, giving them historical value. Akari tells the chef that architects embed their thoughts into buildings, and similarly, he embeds his thoughts into the chocolates, which makes people smile. Encouraged, the chef decides to resume selling. After tea, they encounter the same young boy, who says he has missed the chef. The chef happily announces he will open his stall immediately. Akari reflects that a sweet and adorable new presence has arrived in Neo-Venezia.

Alice Carroll graduates from middle school and feels confident about her future as an undine. Athena invites Alice on a picnic through the countryside canals outside Neo-Venezia. During the boat ride,Athena asks Alice to treat her as a regular customer rather than a mentor. Alice navigates the canals while Athena praises her handling skills and composure. As they pass through a lock, an undine from another company wishes Alice good luck. Alice admits she struggles with singing canzone, the only area where she lacks confidence. Athena reassures her that expressing genuine love for the song matters more than technical perfection. They arrive at the Hill of Hope, where Akari, Aika, and company officials wait with a promotion exam setup. Alice performs a canzone for the examiners, then Athena removes both of Alice's Pair gloves. The removal of both gloves promotes Alice directly to Prima Undine, skipping the Single rank entirely. Athena bestows the title 'Orange Princess' upon Alice for this unprecedented achievement. The next episode follows Alice as she adjusts to her new responsibilities as a Prima and the changing dynamics with her fellow trainees.

Alice works her first day as a Prima undine. Akari and Aika secretly observe Alice from a distance. Aika steps on Aria President's tail,and the scream reveals their hiding place. Alice asks for their honest opinions about her performance. Aika says Alice moved as stiff as a toy robot. Alice agrees and adds she looked like a zombie. Akari suggests moon-gazing that night to lift Alice's spirits. The three friends gather that evening with moon-viewing rice dumplings. Aika secretly invited Al, a Gnome, but he has not arrived. Alice teases Aika about her feelings for Al. Flustered, Aika leaves to find Al. Al explains his overtime work delayed him. While walking together, Aika climbs onto a well and falls inside. Al reaches down to pull her up but loses balance and falls in as well. Both fail to climb out. Maa President appears, and Aika throws the cat out of the well to fetch Alice. Inside the dark well, Al explains how Aqua's two moons influence each other through gravity. He presses his back against Aika's back to demonstrate. Aika becomes emotional and cries, saying they are too close. Her stomach growls, breaking the tension. Akari and Alice arrive and lower a rope to pull them out. After escaping, Al takes Aika's hand as they walk back. Aika does not pull away. The episode closes with Al still holding her hand, leaving the status of their relationship uncertain.

Akari meets a mailman named Udo wearing a bright orange uniform. Udo delivers a handwritten letter each morning to Shima,an elderly woman running a small shop on a quiet canal. Shima opens each letter eagerly, believing her son in the city wrote them. In truth, the son stopped contacting Shima years ago. Udo composes every letter himself, signing the son's name. He writes about fictional promotions and new friends to maintain Shima's hope. Udo walks a long delivery route that takes him past Shima's shop first. Akari notices Udo pausing on a bench to write before each delivery. She follows him and sees him carefully folding paper and addressing an envelope. Udo confesses that a postman once wrote similar letters to his own mother after he left home without contact. That act of kindness saved his mother from despair, and Udo vowed to pass it on. Akari helps Udo deliver a letter during a sudden rainstorm, and Shima invites them in for tea, unaware of the deception. Returning to Aria Company, Akari faces her own upcoming evaluation for the Prima Undine rank.

Akari and Aika meet for their joint practice session. Aika announces she can no longer continue these sessions because she has achieved the rank of Prima Undine. Himeya Company grants Aika the title of Rosen Queen and assigns her to manage a new branch office. Akari notices Aika cried over this promotion and asks Alicia about it. In response,Alicia schedules Akari’s Prima examination for the following day. Akari grows too anxious to sleep that night and practices rowing alone until late. Rain falls on the morning of the exam, but Akari refuses to postpone the test. The weather clears by afternoon, allowing the examination to proceed. Alicia guides Akari through the city as part of the test. Friends and acquaintances greet Akari along the route, and Akatsuki with Woody cheer for her from the Rialto Bridge. Alicia directs Akari into an exceptionally narrow and difficult canal. Akari navigates this challenging passage successfully. Alicia then gives Akari the choice of their final destination, a decision that determines what kind of Prima she will become. Akari chooses to end the journey at the Aria Company headquarters. Alicia thanks Akari for coming into her life, removes Akari’s glove, and promotes her to Prima with the title Aquamarine. Alicia then states she has something important to tell Akari.

The morning after Akari Mizunashi passes her Prima examination,Aika S. Granzchesta, Alice Carroll, and Akatsuki Izumo confront Akari to demand confirmation about Alicia Florence's retirement. Akari confirms the news: Alicia retires from being an Undine to marry and work for the Gondola Association. Akari blames herself for not becoming more reliable sooner, believing her slow progress delayed Alicia's plans. Alicia admits she purposely held back Akari's promotion exam because she did not want to leave her apprentice. Over the following days, Alicia methodically hands over the daily operations of the Aria Company to Akari. Akari eventually breaks down crying inside the empty company office. Alicia finds her, embraces her, and confesses she delayed the exam to prolong their time together as mentor and student. The retired Mr. Mailman hires Akari for a private gondola tour and promises to refer customers to her new Prima service. All the Undines of Neo-Venezia participate in Alicia's formal retirement ceremony. At the ceremony, Alicia hands her oar to Akari as the official transfer of the Aria Company. On the final morning, Akari sees the office filled with memories of Alicia and her friends. She then opens the reception area's shutter to let in sunlight and her new beginning as the company's sole operator. In an afterword, Akari tells Ai about the other characters' futures: Athena becomes an opera singer, leaving Akira as the undisputed top Prima, and Ai arrives for her first morning as a new Pair apprentice at the Aria Company. Akari watches Ai eat breakfast and repeats Alicia's earlier gesture, telling the nervous girl she is simply happy, as the cycle of mentorship continues.