One day, Aida Mana received a wedding dress from her mother and grandmother that they had worn in the past. While thinking about who she would wear this besides someday herself, a mysterious man named Marsh appears, and Mana is thrown back into the past. She was happy to see her grandmother she loved and her old dog Maro, but she then realizes that Alice, Rikka and Makoto are not there because their memories have been altered. In order to save precious memories, the future, dreams, and hope, Mana transforms into Cure Heart.
One day, Mana receives a wedding dress from her mother, which was previously worn by her late grandmother and her mother. Later, whilst discussing their elementary school days with Alice, Rikka, and Makoto, Mana recalls owning a dog named Mallow, who died when she was little. That night, a mysterious man named Marsh uses a clarinet to call forth forgotten and discarded objects that still feel they have use, combining together into a giant whale-shaped blimp in the sky. Marsh, who Mana doesn't seem to recognise, starts trapping people inside film reels, forcing them to relive their past memories for eternity, depriving them of their futures. He then summons three henchmen; Purple Buggy, Silver Clock, and Mannequin Carmine, to fight against the Cures, reassembling them no matter how many times they are destroyed. Overwhelming the Cures, Marsh traps them inside their own memories, with Mana finding herself in her elementary school days when both her grandmother and Maro were still alive. Meanwhile, Sharuru and the other fairies are approached by Bebel, a former acquaintance of Marsh, who informs them that they must venture inside the memories of their partners in order to save them. As Mana tries to find a way back to the real world, she finds the memories in this world are different from her own, as Rikka and Alice are nowhere to be found, but seems to enjoy being with Mallow. With help from Bebel, Sharuru and the others dive into their partners's memories, with Sharuru joining Mana just before she learns Mallow was hit by a car, which ends her film reels when she gives into the grief of losing her beloved dog. Cautious about Bebel's words that Mana will never give up, Matthew sends his henchmen after Rikka, Alice, and Makoto, deeming them a threat. Rikka and Alice manage to find each other within their memories, soon joined by their partners, whilst Davi convinces Makoto not to run away from the reality of the Trump Kingdom's situation. Rikka and Alice fight off against their opponents whilst Makoto is assisted by the arrival of Aguri, Cure Ace. Meanwhile, Mana, who can't stand returning to a world without Mallow, receives words of encouragement from her grandmother, allowing her to hear the support of her friends and find a way back to her world along with the others. As Marsh transforms into his true form, Mana, realising that Marsh is actually Mallow himself, takes on his attack, stating she has never once forgotten him, helping him to see the light. Just then, the clarinet that had been influencing Mallow travels forward in time to try and destroy the Cures's future. Using the Miracle Bouquet Lights, the Cures travel forward in time to the day of Mana's wedding and, with help from Mallow, reach the clarinet, who proves resilient to the Cures attacks and delivers a critical blow to Mallow. Being left with no regrets, Mallow leaves behind his psyche, which gives Mana the powerful Engage Mode, allowing her to defeat the clarinet. After the girls return to the present and everyone who was imprisoned is freed, Bebel takes care of Maro's psyche, revealing herself to be Mana's grandmother.
- Aida Mana (相田 マナ Aida Mana?) / Cure Heart (キュアハート Kyua Hāto?) - The bright and energetic student council president of Oogai First Public Middle School in her second year. She is a person who believes actions speak louder than words, and will often jump in to help others without even thinking about it. Both elders and youngsters around her believe in her leadership capabilities.
- Hishikawa Rikka (菱川 六花 Hishikawa Rikka?) / Cure Diamond (キュアダイヤモンド Kyua Daiyamondo?) - The student council's secretary in Oogai First Public Middle School. She is Mana's childhood friend. She was always protected by her back then, which makes Rikka always believe in Mana, but Rikka always protected Mana when she was a troublemaker. She is also one of the ten best students in national mock exams.
- Yotsuba Alice (四葉 ありす Yotsuba Arisu?) / Cure Rosetta (キュアロゼッタ Kyua Rozetta?) - A student in Nanatsu Hashi Academy for girls, which only rich people can afford because she is the heir to the Yotsuba Zaibatsu. She is childhood friends with Mana and Rikka. She is a kind person, sweet, talented and gentle, but often flaunts wealth involuntarily.
- Kenzaki Makoto (剣崎 真琴 Kenzaki Makoto?) / Cure Sword (キュアソード Kyua Sōdo?) - The royal guard of Trump Kingdom in parallel worlds. She came to Japan to find the princess after her nation was invaded and became a super idol and extremely popular fashionista. Cool and always has a strong sense of responsibility, but harbored remorse for feeling that she did not protect the princess, and doesn't get along well with her new allies.
- Madoka Aguri (円亜久里 Madoka Aguri?) / Cure Ace (キュアエース Kyua Ēsu?) - A mysterious Cure who appears, helping the Cures. She is smart and very wise.
- Sharuru (シャルル Sharuru?) - Heart's rabbit-like fairy partner. The most passionate of all the four mascots, she has a passionate heart and always works hard. She ends her sentences with "~sharu".
- Raquel (ラケル Rakeru?) - Diamond's dog-like fairy partner. She is very reliable to the other fairies, much like her partner. She ends her sentences with "~quel".
- Lance (ランス Ransu?) - Rosetta's bear-like fairy partner. He is the youngest out of the four mascots and a little spoiled. He ends his sentences with "~(de) lance".
- Dabyi (ダヴィ Dabii?) - Sword's cat-like fairy partner. She is very independent, but she often worries about her partner. She ends her sentences with "~(da)byi" Davi is able to transform into a human, and acts as Makoto's manager under the name "DB". It is currently unknown whether or not the other fairies have human forms as well.
- Ai (アイ Ai?) - Ai, who is also called Ai-Chan by the Pretty Cure girls of this season, is the baby mascot who made her first appearance in episode 8. As a baby, she cries and mostly smiles, but never says a word as she is too young.
- Marsh (マシュー Mashuu?) - A mysterious man who plays the clarinet.
- Mannequin Carmine (マネキンカーマイン Manekinkāmain?) - A woman who works for Marsh.
- Silver Clock (シルバークロック Shirubākurokku?) - A mysterious looking clock who also works for Marsh.
- Purple Buggy (パープルバギー Pāpurubagī?) - A mysterious looking robot who also works for Marsh.
- Maro (マロ Maro?) - Mana's grandmother's pet dog and Marsh's dog form.
- Bebel (べベル Beberu?) - A mysterious mascot who turns out to be Bando Isuzu.
- Bando Isuzu (坂東いすず Bandō Isuzu?) - Mana's grandmother.
- Clarinet (クラリネット Kurarinetto?) - A sentient clarinet working alongside Marsh and the true villain.
- Princess Marie Ange
- Aida Kentaro
- Aida Ayumi
- Bando Sokichi
- Hishikawa Ryoko
- Hishikawa Yuuzou
- Yotsuba Seiji
- Nikaidou Takuya
- Momota Tsubasa
- Yashima Chihiro
- There are small differences and errors in the scene where everyone is clapping for Mana who had just been married between the trailers and the movie itself:
- Rikka, Alice and Makoto wear the dress they had in the opening. Rikka's hair is down and she is wearing a long-sleeved blue dress, Alice has the same hairstyle from before and is wearing a long-sleeved dress similar to Rikka's, and Makoto is wearing a purple dress with white long-sleeves and her hair is shoulder-length. But in the movie, Rikka's hair is in a ponytail and she is wearing a blue dress with a small blue jacket, Alice has her hair in low curled bun-like pigtails and is wearing a yellow dress covered in transparent silk, Makoto has the same short hair (not shoulder length) and is wearing a pink hair clip and a long-sleeved purple dress.
- Aguri wasn't shown at all in the trailers. She is placed on the right side of Rikka in the scene, wearing a red dress and red silk with much shorter hair. The reason why she was not in the trailers is because they came out before her debut.
- Yuuzou's hair color was pink and his skin was darker. These get fixed in the movie.
- Sebastian didn't wear his gloves. He wears them in the movie.
- Davi gets replaced by Yashima. She wears a black one-piece dress underneath a red cardigan.
- There are no lighting during the scene. The trailers had sunlight shining above the crowd.