Flash and his friends arrive at the ocean city of Vocanctus, just in time for its annual Voice of the Ocean Festival, to give thanks and prayers to the protector of the city, the Legendary Pokémon Sirenity. While exploring the city, Flash meets Sonata Dusk, a young girl suffering from a recent tragic event, who just so happens to have a special connection to Sirenity. As Sonata finds herself targeted by the criminal Guile Hideout, hoping to use her to gain control over Sirenity for himself, Flash must help Sonata come to terms with her past and find the strength to fulfill her duties and save Sirenity and the city from destruction.
- Actually Pretty Funny: When Flash encourages Sonata, when she is afraid she will mess up performing her song in front of the whole town at the festival the next day, Flash assures her nobody will even know if she messes up because he was told only Sonata's family speaks the language they use when they sing. He comments she could sing an old TV theme song and no one would even know, making Sonata laugh.
- Adaptational Heroism: One of the movie's most significant deviations from the canon MLP series is that Sonata isn't evil, but instead a Broken Bird traumatized by the loss of her sisters and needs help overcoming her grief. The same could even be said of the Dazzlings, who never pose a threat to the protagonists and sing to Sirenity to keep Vocanctus afloat.
- Aside Glance: When Sonata explains to everyone that only her family is allowed to learn her special song, she comments that as the (apparent) Sole Survivor of her family she will need to teach it to the next generation, so only her kids and their father will learn it. As she says this, she has a coy smile and briefly glances at Flash, with only Springer noticing.
- Awesome Underwater World: As Flash and Sonata ride on Sirenity underwater, they get to see the wondrous environment around them, inhabited by all sorts of Water-type Pokémon.
- Aw, Look! They Really Do Love Each Other: Despite how the Dazzlings constantly annoy and throw insults at each other, at the end of the day they are still sisters and love each other above all else. When Sonata thought that Adagio and Aria died she entered a deep depression for a year and became a Broken Bird. When Adagio and Aria are freed from Malamar's control they remember the whirlpool they were in and then immediately ask where's Sonata when they notice her absense.
- Beware the Nice Ones: While Serenity is kind enough to protect the city of Vocanctus, it's also revealed to not be a Pokémon anyone should trifle with when it uses a whirlpool to kill Guile.
- Brainwashed and Crazy: Guile was the one responsible for Adagio and Aria's disappearance so that he can use their voices to control Sirenity. He was originally going to capture Sonata too, but she inadvertently escaped capture. He also eventually suceeds in gaining control over Sirenity, until Sonata manages to free her.
- Character Development: Over the course of the "movie", Sonata starts out as a depressed Broken Bird still traumatized by the supposed deaths of her sisters. However, thanks to Flash and his group, Sonata overcomes her grief and regains the confidence to start singing again.
- Face Fault: All of Flash's friends do this when he asks them what Sonata said to him, being the only member of the group to not hear her Love Confession for him due to the noise from the crowd.
- History Repeats: Guile, also known as Archie, the former leader of Team Aqua, was punished by Kyogre, a Legendary Water-Type, for trying to control it by having a curse placed on him. When his plan to try controlling Sirenity fails as well, he once again finds himself faced with the wrath of a Legendary Water-Type, with Sirenity drowning him.
- Karmic Jackpot: Sonata goes out of her way to help Springer get some water from the metal tap, despite having no reason to, causes her to be noticed by Flash and for him to go out of his way to rescue her and help her work through her depression by encouraging her. Essentially, one random selfless act ultimately ended up improving her life for the better.
- Love Confession: Before she performs with her sisters, Sonata confesses her crush to Flash. Ironically, everyone hears this, except for Flash because the noises of the crowd were too loud.
- Mercy Kill: Sonata notes that in a way, Sirenity drowning Guile is showing him a mercy, since without his armor he would have just kept suffering and experienced a slow and painful death anyway.
- Pet the Dog:
- Even while Sonata is in the middle of her deep depression over the loss of her sisters, she still takes the time to help Springer get some water when she notices him trying to get some from a metal tap, despite having nothing to gain from it herself. When she sees how happy he is from it she briefly cracks a small smile before running off when Flash shows up.
- While Guile did brainwash Adagio and Aria, he did keep them well-fed and healthy under his control.
- Poor Communication Kills: When Flash and Springer first enter the temple, looking for Sonata, Sirenity attacks them for intruding. Luckily Sonata calls her off, explaining that they helped her earlier and don't mean any harm.
- Reasonable Authority Figure: Mayor Novo does everything she can to protect the people of Vocanctus as Guile threatens to destroy everything with Sirenity under his control.
- Red Eyes, Take Warning: When Sirenity falls under Guile's control her eyes begin glowing a bright red color. When Sonata frees her from Guile's control her eyes go back to normal.
- Rescue Romance: A one-sided example between Flash and Sonata. Flash goes out of his way to save Sonata when she is attacked by Black and White, and after he continues to try to help her by encouraging her to work through her grief and introducing her to the rest of his friends, she starts to devlop a crush on him, including giving him a few suggestive looks. When he once again saves her from Guile and encourages her to use her power to save Sirenity, he ends up becoming the one person she trusts the most, and falls in love with him. Though Flash never realized her feelings for him himself.
- Villains Want Mercy: After Guile is defeated and his plans are ruined, he is reduced to a cowering wreck when his armor is destroyed and he is cornered by Flash, Sonata, Flash's Pokémon, and Sirenity, saying that everything was just a "big misunderstanding".
- Well-Intentioned Extremist: Guile, once known as Archie, is a terrorist who wants to flood the planet so that there would be more places for Water-type Pokémon to live.
