The girls go on a picnic trip out into the woods. They decide to camp out on a creek nearby to eat for lunch. But then, they hear an ominous presence nearby. Suddenly, a girl with a turtleshell jumps out of the bushes to attack, but it foolishly falls into the river. Larimar jumps into the water to help her, but discovers the river is just shallow.
After pulling the girl ashore, they check to see if she's okay. She wakes up, then sees the girls and she became frightened. The girls tries consuling that they tried to help her after jumping out of nowhere and almost drowning in the water. Though embarrassed of her own clumsiness, she thanked the girls for saving her. But then she passes out for no reason.
So the girls took the mysterious child back home. Shortly, Sakutarō is thrilled to discover that the girl is actually a kappa, a species of legendary monsters that are neither human nor animal. He also denotes they must stay moist with water. Excited see a real kappa, he wants to thoroughly study the girl, but Airi is worried about harrassing her. She argues with him that he usually denies mythical stuff as he is obsessed in science, but Sakutarō rebutts that even science can try to understand mysteries and unconfirmed legends, to Airi's astonishment of his own hypocrisy.
Larimar tries introducing herself to the girl and to everyone. As she opens up, she also introduces her name is Miya. She then simpily tells them that she wanted to 'frightten' them. This left Larimar confused, but Sakutaro clarifies that kappas are mischevious and love to surprise people. She also tells them that she tried so many times to scare people but is unable to, and that she can't swim. In fact, she doesn't have the courage to scare anyone. And if she continues being unable to scare anybody, then her kappa cohorts will make her leave their group. So everyone decide to help her have the will to surprise people.
To start off, the Jewelpets pulls pranks on Sakutarō to display the reaction of being "surprised." Though, this leaves Sakutarō somewhat annoyed. Later, the girls make a ghostly prank on Sakutarō that he faints in fear. Miya now feels she is starting to enjoy surprising people.
Content, Larimar asks her that they test her courage, by appearing in a talent show with her. But Miya becomes concerned, saying that since she is a kappa, she is made to tricked people since early times and is not accustomed to being a 'nice kappa' to the humans. But Larimar insists she is cute and regardless of her status, she can be popular. She also assures she can use magic to help her be cute. So she casts a spell on Miya to make her pretty, giving her an idol-like costume to wear.
When everyone gets to the talent show, Miya finds herself on stage and, surprisingly attendance is low. Miya becomes nervous, but Larimar encourages her to do something. She then makes an unenthusiastic koala impression, astonishing the Jewelpets in disbelief but leaves the audience uncontent. Miya tries another attempt, by spinning two plates on two sticks. This slightly impresses the audience. So Miya continues to keep spinning, but later it becomes stale and Miya beginning to be discouraged.
Larimar tells Miya to not give up. She signals Airi to proceed with their next strategy. So Airi relays to Sakutarō to start. He presses buttons on his mobile device and starts some dance music through the stage speakers. The Jewelpets hop up on the stage and start dancing, and encourages Miya to dance with them. So Miya begins dancing along with them while spinning plates. The crowd eventually get more interested in the performance and gathering around, starting to clamour for Miya. The Jewelpets decided to help impress the crowd by using their magic to change Miya into a variety of costumes.
For the finale, Larimar signals Sakutarō to take it from here. He ultimately does so on command and he splashes Miya with water, causing the magic wears off and changing her back to her original appearance. Sakutarō then shows to the crowd that she is a kappa. The audience were stunned at sight, and Miya started to assume the worst. However, the crowd ultimately applauds believing the kappa was impressing them, and became a crowd favorite. Miya's friends all gathered around her and congratulated her for performance. Miya became pleased she was an idol and was all thanks to everyone. Larimar then stated that now she can show her resolve now that she is more confident in herself.
The girls returned to the mountains, to bring back Miya back to her other kappas. Miya is still nervous but Airi assured that she's no longer her old self. Then, Airi recieves a rain warning on her Jewel Pad. The sky started raining and begun to soak everyone wet. Though the girls arrived at the same river point where they met Miya. Larimar tells if Miya might be able to cross the river inspite of the torrental current but Luna reminded her that she can't swim. But then, the cliff breaks apart and Larimar falls into the river, getting swept up by the river's rushing current. She hangs on for life on a nearby rock.
Airi quickly asks Ruby to use her magic to rescue her. But Ruby panics as she casts her spell, then makes a useless small ship appear. Labra confidently casts her spell to save Larimar, but makes a haul of saftey equipment pile on Labra. Luna casts her spell and makes a life ring appear, then throws it at Larimar but is unable to reach her. Miya just stands there, being under the assumption on what to do to save her. Then Airi's pendant starts to glow. Airi takes it off and tries to throw it to Larimar, but Larimar loses her grip and becomes swept in by the river current.
Miya gets an idea and asks Airi to lend it to her. Airi gives it to Miya, and then Miya confidently dives into the river. Then she begun swimming towards Larimar and manages to grab her in time. Then she delievers Larimar the pendant, magically changing her into her human form. Then she casts a spell to make the heavy rain disappear. She is then seen floating in a magic bubble with Miya in hand.
Larimar thanks Miya for saving her, but Miya insists she has all the credit. Larimar also noticed that Miya is actually swimming, she replied that she must have forgot how to because she was desperate. Then, Miya's kappa friends appeared and see how gradually she has developed. They all became impressed how she grown and they all accept her. The girls then notice the other kappa and so Miya returned to them peacefully. She then says her thanks and goodbyes to all the girls, telling them they will be best friends forever. Then all the kappas vanish, Miya along with them.
- One of the costumes Miya changes into resembles Funassyi, the unofficial but well-known mascot of Funabashi, Chiba.