Manatsu Natsuumi, an energetic girl, moves to Aozora City from Minamino Island to live with her mother, who works at the city's aquarium. Meanwhile, in the Grand Ocean Kingdom, Laura, a mermaid, is tasked to find humans who can open her assigned Tropical Pact to fight back against the Witch of Procrastination. Following the Mermaid Queen's orders, Laura heads off to Aozora City. Meanwhile, Manatsu arrives at the city, reunites with her mother and explores the city area and aquarium. While taking a break, Laura and Manatsu encounter each other with the mermaid explaining her mission while secretly intending to complete it for her own agenda. Later, a crab general of the Witch named Chongire arrives and creates a monster, a Yaraneeda, from a coconut tree to steal Motivation Power from a group of runners at a beach. Alerted by a strange energy field in an area of the city, Manatsu heads off to confront the monster, believing Laura was in danger. When Laura gets captured, Manatsu resolves to immediately do the most important thing. As a result, Laura's assigned compact opens and grants Manatsu the power to become one of the legendary warriors, the Pretty Cure, foretold in the Grand Ocean's legends. With this new power, Manatsu, now as Cure Summer, defeats the monster and rescues Laura who salvages and returns the stolen Motivation Power. After the battle, Laura and Manatsu befriend each other. Meanwhile, the Witch of Procrastination is notified of the Pretty Cure's appearance, but decides to address the issue later.
