A lonely kid finds something lost and broken in the dark, names it, loves it anyway. By the time you realize what Fu-Chan actually is, the movie has already made you complicit in her choice. Every Cure who ever fought in the name of friendship gets called to answer what that promise actually costs when the person holding it isn't trying to hurt anyone, she's just trying to belong.

Yokohama's Minato Mirai district buzzes with Pretty Cure fever after news of Fusion's defeat spreads through the city. Girls everywhere dress up as their favorite Cures and imitate them, but Sakagami Ayumi, a new transfer student, is left on her own. Walking home from school one day, she comes across a strange creature, names it Fu-Chan, and the two quickly become close friends. Yet Fu-Chan is actually a piece of Fusion and holds the power of darkness. Wanting to make Ayumi happy, it swallows up everything she dislikes, spreading chaos through her school and across the city. All twenty-eight Pretty Cures gather once again to help Ayumi get her true feelings across to Fu-Chan, and when their powers come together, a miraculous light begins to shine. The film is an action fantasy entry in the magical girl genre.