Manatsu Natsumi, a stylish teenager, embarks on a thrilling journey as she moves to the bustling city. Her fascination with the urban delights takes a fantastical turn when she encounters Laura, an actual mermaid in search of the legendary Precure. Tasked with saving the Grand Ocean, Laura enlists Manatsu, who, fueled by her unwavering resolve, transforms into Cure Summer, one of the vibrant Precure warriors. As their team expands with new allies, Manatsu must navigate her chaotic new life, defending humanity's spirit against sea invaders. Facing increasingly challenging battles, the girls must uncover the true treasures that lie within their hearts.