Aria the Avvenire: Sono Atataka na Sayonara wa... (Aria the Arrived: That Warm Goodbye...)
The story begins with Ai relating a story to Akari of her experiencing a "miracle" while she was practicing. She saw Cait Sith as she was traveling down an unfamiliar path. When she disembarks from her gondola to follow it, she meets two Single undines from Himeya company and Orange Planet in the middle of practice.
[Source: Anime News Network]