Whilst running to the first day of her new school, the happy-go-lucky Miyuki Hoshizora encounters a fairy named Candy, who leaves behind a pink book. As Miyuki has trouble introducing herself to the class, her classmate Akane Hino helps her to break the ice. As Miyuki checks out the library later that day, she discovers a mysterious entrance, taking her to a strange place where she learns Candy is being chased by a wolf named Wolfrun, who starts making the people in the town fall into despair and steals their 'bad energy' with a goal of ressurecting someone named Pierrot. As Miyuki strives to protect Candy, she is given a magical item known as the Smile Pact, using it to transform into a PreCure named Cure Happy. As Miyuki becomes reluctant to fight, Wolfrun summons a monster known as an Akanbe to fight against her, but with help from Candy, Miyuki manages to realise her power and defeat it, receiving an item known as a Cure Decor.

As the girls prepare to go on a school trip to Kyoto, Candy becomes upset when she isn't invited. Meanwhile, Pierrot's right hand man, Joker, gives Wolfrun, Red Ogre and Majorina special blue noses which doesn't require Cure Decors to summon Akanbe. Candy tries her hardest to help the girls plan their trip, only to make things worse. She runs off, feeling she is unwanted, and gets captured by Wolfrun. Wolfrun then confronts the girls and uses the blue nose to summon a Gumball Akanbe, which proves resilient against the Cures' attacks. As the Cures find themselves helpless, Candy breaks free and, upon hearing the kind words of the Cures, brings forth new Decors which allow the Cures to perform a new attack, Rainbow Healing, to defeat the Akanbe. With their team powered up, the girls decide to take Candy along with them on their trip.

When their class is asked to learn the meaning of their names, Yayoi struggles with personal feelings regarding her deceased father and a secret they shared.