While investigating the legend of the mythical Pokémon Arceus, Ash, Goh and Dawn uncover a plot by Team Galactic that threatens the world.
Neo-Venezia has reached a long winter. Ai, Azusa and Anya, who were practicing jointly in the cold weather, visit the Undine Museum, led by Akira who seems not her usual self. At the museum, the trio meet its director, Asuka who is Akira's senior known as Himeya's legendary undine. The two of them are the successors to a gondola that has been carefully passed down since the founding of Himeya Company. However, Akira reveals that Aika, who is expected to inherit the gondola, has no intention of doing so. Azusa, who is not convinced, tries to find out why.
The season is fall and the city of Neo-Venezia is covered in fallen leaves. Something is bothering Anya, who works at Orange Planet. Her senior colleagues Alice and Athena haven't seen each other due to their busy schedules, which is making Athena feel sad. But for some reason, Alice seems to be avoiding her altogether. With her friends Ai and Azusa's help, Anya tries to find a definitive way for Alice and Athena to get together. But during this time, Anya learns of a situation that only she can see because of where she stands.