As Pretty Cures all over the world fight against Saiarks, minions of the evil Phantom Empire led by Queen Mirage, Himelda "Hime" Window, also known as Cure Princess, feels downhearted after losing yet again to the Saiark, having to be bailed out by another Cure named Cure Fortune. Blue, the god of the universe, gives Hime a Crystal of Love so that she can find a partner to fight alongside her. Excited to be able to have a friend, Hime decides to randomly throw the crystal to decide her partner, which randomly lands on a girl named Megumi Aino. Hime, along with her fairy partner Ribbon, follows Megumi as she goes about her shopping, helping others when they're in trouble.

Fearing she might lose to the Saiark yet again, Hime decides to escape with Megumi to her hideout. There, Blue explains how the Phantom Empire emerged from a sealed box known as Axia and began plaguing the world with Saiark, including Hime's homeland, the Blue Sky Kingdom. Hime, feeling she has no chance of winning against the Saiark and is a failure as a Pretty Cure, runs off, prompting Megumi and Ribbon to chase after her. Using special items called PreCards to don a magical detective outfit, Megumi, aided by her friend Yuko Omori who had ran into Hime earlier, manages to find Hime and give her some encouragement.

Blue gives Megumi and Hime some Cure Line phones, so they can keep in contact with each other, before urging them to keep their identites as Pretty Cures a secret from their friends and families. However, Megumi has a hard time keeping things a secret from Seiji, who lives next door to her. The next day, during his morning run, Seiji encounters a Newspaper Saiark being led by another one of Queen Mirage's commanders, Hoshiiwa. Arriving on the scene to find Seiji beating up by the Choiark, Megumi and Hime choose to transform in front of him to protect him. After Megumi beats the Choiarks with her new form, Cherry Flamenco, she and Hime team up to defeat the Saiark. Afterwards, the girls, along with Blue, explain their situation to Seiji, who decides to help them out in fighting against the Saiark.

Hime is transferred into Megumi's school under the Japanese name Hime Shirayuki, becoming excited at the thought of making 'one hundred friends'. Upon arriving at school however, she is overcome with fear and finds herself unable to face anyone properly. Megumi tries to get Hime to make friends with Yuko, but she becomes too afraid and turns away from her. Whilst lamenting her actions alone in the gym storage, Hime meets a teacher having his own worries about his students not listening to him. Just then, Namakeruda appears and uses the teacher to create a Cone Saiark. Hime initially struggles against the Saiark, but becomes strengthened by her desire to protect the school and make some friends, defeating the Saiark with help from her new form, Sherbert Ballet. Afterwards, Hime gives the teacher some words of encouragement before working up the courage to become friends with Yuko.

On their way to Megumi's house, Megumi and Hime end up doing a lot of good deeds, such as clearing up litter, treating a injured puppy, helping a lost child, and giving someone courage to propose to his girlfriend. After having pancakes with Megumi and her mother, Hime laments how her parents were trapped inside mirrors by the Phantom Empire, whilst Megumi tells her how she wants to help out her mother, who has a weak body, citing her as the reason she loves helping others. Hosshiiwa takes advantage of Megumi's helping nature to lure her and Hime into a trap, attacking them with a Mole Saiark. As Hosshiiwa passes off Megumi's desire to help others as self-satisfaction, Hime stands by her side, believing in the genuine good feelings from helping others, and manages to break them free from the Saiark and defeat it. Afterwards, Megumi gives Hime her thanks for standing by her beliefs.