It's an exciting day for fashionable teenager Manatsu Natsumi, who is moving into the big city for the first time. Upon arriving, Manatsu is immediately charmed by the city's spectacles. However, things take an unbelievable turn when she encounters Laura—a real-life mermaid!

Laura is searching for the Precure, a group of radiant warriors who may have the key to rescuing Grand Ocean, Laura's home. This duty soon falls upon Manatsu, whose unwavering determination causes her to awaken as one of the Precure: the vivid Cure Summer. As new friends join the team, Manatsu needs to adapt to her hectic, new life while protecting humanity's liveliness from oceanic invaders! With each battle more difficult than the last, the girls must discover what is truly valuable to them.