The Umishou team has arrived at the Ninagawas’ house on Daito Island, where they prepare for the Inter-High tournament. They meet Amuro’s family, tour the island and train a bit as well. Kaname gets closer to Mirei, but into trouble with Amuro and is kissed by a mysterious person. After forgetting to pay attention to time, they manage to make it to Inter-High just in time for the first race. Before their race on the third day Momoko is proposed to by Taku and Amuro confesses kissing Kaname. They both have a good start, but then something happens…
At the Ninagawa house on Daito Island Kaname, Makio and Momoko notice the similarities between Amuro and her mother, Kiriko. When Amuro introduces Kaname to her family, they clearly misunderstand their relationship, which causes Maaya to claim Kaname is hers. Kiriko tells Maaya she has lost to Amuro in the ‘breast department’, angering her, of course. Meanwhile, Masashi tells the Umishou members that although the island is pretty, it is also hit by typhoons all the time. The next day Amuro shows them around the island, promising to take them to her private beach as well. On their way Sanae cannot control herself any longer and strips to show off her new bikini. Momoko tells her they did not go to Daito Island to play around, but Sanae replies that there must be some time for that as well and starts using her charms on Kaname. A jealous Maaya decides to show off her bikini as well, followed by Makio. And when Sanae checks Momoko’s bag, she discovers Momoko has packed a bikini as well. After a long walk they finally arrive at Amuro’s beach, which turns out to be a cliff to jump from with a rope attached to its side to climb back up. While Amuro explains the island has no sandy beaches, Mirei promises to show Kaname her swimsuit later when they are alone.
After waking up from a dream about Mirei’s swimsuit, Kaname discovers that the room, in which all of the swimming club members are sleeping, is part of a noodle shop run by the Ninagawas, without any partition between it and the rest of the shop. When everyone else is awake, the club members follow Amuro to the local elementary and middle school’s pool for practice. There, Kaname is surprised to see Momoko is wearing a bikini as well. Just when Mirei is about to undress and join the others in the pool, a bunch of neighborhood kids arrive, making further practice impossible. Sanae wonders if the pool is still open after dark and Amuro suggest they visit the Daito cave in the mean time. Soon after arriving everyone decides to go exploring the cave on their own or in pairs. Maaya, seeing an opportunity, runs off dragging along Kaname, until he slips and glides down into another part of the cave. There, he finds Mirei, who lost Makio.
Lost inside the Daito cave, Kaname and Mirei try to find their way out. They both feel conscious about each other and when they take a break conversation turns out to be difficult. When Mirei mentions her shirt got completely soaked, Kaname notices her bikini underneath and realizes it is a very small one showing lots of skin. As Kaname gets more nervous after what he just saw, Mirei realizes the cave is inhabited by bats and in panic she starts clinging to Kaname. Meanwhile, as the sun sets, the others are waiting for them outside the cave. Amuro tries to calm everyone down by stating that when she got lost as a kid, it only took her two days to get out. Not much later Kaname and Mirei appear and they all return to Amuro’s house, where during dinner Masashi has a good laugh hearing about Kaname and Mirei getting lost. Sanae, realizing they have not seen Mirei’s swimsuit yet, tells Mirei to strip and show it to everyone. Kaname tries to change the subject, but when Masashi tells her she cannot stay for the night unless she shows her swimsuit, Mirei decides to strip, showing them a fairly normal bikini. It turns out that after returning from the cave she had a shower and changed into it. During practice that evening, Kaname is still not past the shock of expecting to see Mirei in her other swimsuit.
After practice the Umishou members are cooling down in the sea. Kaname, feeling a bit left out, is sitting on some rocks guarding everyone’s bags, while Amuro and several other girls are having a diving contest. Mirei, not participating in the diving contest, joins him and suggests he dips his feet into the ocean. Sanae spots them and comments about them being close, which causes Amuro to get jealous. Later, back at the Ninagawas’ house, Kaname notices Amuro still seems angry with him. When Sanae comments on having seen the entire island in just two days, Masashi decides to take them to a special place he has saved for last. Driving everyone to this place Masashi notices something about Amuro as well. After some time Masashi stops his pickup truck in the middle of nowhere and tells everyone to get off and lie on their backs. When he switches off the truck’s lights they see a spectacular starry sky. Then, Kaname suddenly feels a hand grabbing his hand.
Kaname is wondering who is holding his hand and starts fantasizing about who it might be, when Sanae yells she saw a shooting star. Kaname realizes that to find out who it is he has to listen carefully who is saying something until there is only one possibility left. After some time, when Momoko, Makio and Maaya are eliminated as well, the mysterious person suddenly bends over him and kisses him. Soon after this, Masashi tells them it is time to go and switches the truck’s lights back on. Kaname finds himself staring into Ikamasa’s face, but when Ikamasa starts rolling around, Kaname realizes he must have made a rolling sound he heard earlier, which eliminated Ikamasa as well. Kaname decides this leaves Amuro and Mirei and he notices both are blushing, confusing him.
After someone kissed him, Kaname is unable to sleep and the next day during training Kaname is still wondering who it was. He does notice Amuro still seems angry with him. As he wonders what to do, Momoko tells him they are almost out of drinks and orders him to get some more. While he is filling a bucket of water Mirei appears, looking for a toilet. After showing her the way, he thinks that if he grabs her hand, he might notice if she is the mysterious person. But instead he messes up and grabs her butt, causing Mirei to hastily leave, wondering if Kaname’s behavior has anything to do with the previous night. Later that day Kaname is sitting near the Ninagawa house, still thinking about all that happened when he realizes someone is staring at him. It turns out to be Amuro who came calling him for dinner. Walking back, he decides to grab her hand, but fails to recognize if it was the mysterious person’s hand. This action does cheer up Amuro, though.
The next morning Amuro is still in a good mood. Kaname, who, again, could not sleep, decides that because her mood improved after holding hands the previous day, Amuro most likely is not the mysterious person. Which leaves Mirei, who must hate him by now after he grabbed her butt. Seeing something is bothering Kaname, Ikamasa offers his help. Kaname tells him about the holding hands part and that he suspects Mirei. After making a mess of asking Mirei about it, Ikamasa tells Kaname to lie in a ditch and plans to let Mirei trip and fall on top of him. But before Ikamasa returns with Mirei, someone else trips and falls on top of Kaname: Kiriko, who was trying to recover some panties that were blown away by the wind. Arriving shortly after this, Ikamasa apologizes to Kaname, spilling his plan to Mirei, causing her to run away. When she trips, Ikamasa quickly reacts by throwing Kaname in her path to block her fall. His screaming in agony when Mirei’s knee accidentally hits a sensitive part alerts Amuro, who, seeing them like that, gets angry again.
The following morning Amuro’s mood is terrible. Kaname, recovering from Mirei’s knee and being hit with a couple of pineapples by Amuro, is still in bed thinking about all that happened, when Amuro’s sibling Riru brings him breakfast. He decides to tell Riru a story about his situation, as if it was someone else’s, but Riru quickly realizes it is about Kaname, Amuro and Mirei and tells him to confront both of them. He will first ask Mirei about that night and a bit later Riru will bring Amuro so he can ask her as well. But just when Kaname tells Mirei he believes it was her that kissed him, Amuro already arrives, overhearing him, and again she runs away. Back at the house, Masashi comments a typhoon has arrived.
Kaname calls after Amuro as she runs away. Mirei interrupts him to tell him it was not her that kissed him; she merely blushed because she saw him kiss someone. As Kaname realizes his mistake, Masashi arrives, telling them to return to the house because of the approaching typhoon. Realizing something happened between Kaname and Amuro, Masashi tells him Amuro most likely ran to “Grandma Rock”, a rock from where her grandmother used to swim. Kaname, deciding to go after her, asks for directions and leaves. Returning to the house with Masashi, Mirei realizes Kaname must like Amuro. Meanwhile, after a hazardous walk under worsening weather Kaname spots Amuro on a rock just off the cliff. Thinking she is planning to jump off it, he hurries towards her to stop her, but he trips and falls towards the sea. Luckily Amuro, still angry, manages to grab his hand, saving him.
Their backs facing each other, Kaname and Amuro are sitting on Grandma Rock. Kaname, trying to get her to talk to him, tells her he heard from her father about the rock and her late grandmother. Amuro angrily tells him her grandmother did not die and her X´s are not mementos; she plans to return them when her grandmother returns. Kaname decides to apologize for him ignoring her feelings and believing the mysterious person was Mirei. He partially blames her though, for suddenly kissing him and keeping quiet about it. A sudden wave collapsing onto the rock caused him to jump into Amuro’s arms in panic, but instead of getting angry again, Amuro laughs and calls him a wuss. She decides to kiss him and says that they are even now. When the storm dies down a bit they manage to safely return to the Ninagawas’ home and everything seems fine again. But the Umishou members are unaware that something is wrong…
The next day everyone is relaxing after breakfast and Kaname is glad everything ended well. He also notices Riru likes messing with him. But after hearing a weather forecast on a radio the time to relax comes to an abrupt ending: Kaname realizes the Inter-High tournament starts that very day. Everyone starts to panic, since it took them 10 hours to get to the island, but Masashi tells them it will take only an hour to return to Okinawa by plane. The only problem is that it only flies once a day and the next flight will leave in half an hour. They quickly pack and Masashi drives them to the airport, where they arrive just in time. Before boarding, while one of Amuro’s youngest sisters is trying to make Maaya promise she will return (the youngest Ninagawas seem to love her), Riru hands Kaname a letter. After taking his seat in the plane, he opens the letter and reads that Riru is the one that kissed him. Shocked, he finds Amuro reading over his shoulder, but to his surprise Amuro tells him it is fine if it is Riru. When Kaname clearly fails to understand why, she explains to him that Riru is not her little sister, but her little brother. As she explains Riru loves to play pranks and cross-dressing seems to be his favorite, Kaname looks out of the departing plane’s window to see Riru sticking out his tongue and lifting up his dress.
After arriving in Okinawa’s capital, Naha, the Umishou members decide to hitchhike to the tournament’s venue, since they spent all their money on the airfare. Maaya has already changed into her swimsuit at the airport, for she has to swim that very day. After several cars passed them without even one slowing down, Maaya decides that, seeing another car approaching, it is time for drastic measures and lifts up Mirei’s shirt. The car, almost crashing, stops and after Momoko explains their situation, the driver is willing to take them to the venue. Everyone manages to fit into the tiny car, although Mirei’s chest is squished against a passenger window and Maaya’s butt is in a similar position against the back window. After about half an hour they arrive just in time for Maaya’s first race; the staff was about to disqualify her for failing to show up. Despite being still exhausted from running the last bit, she manages to fire herself up and qualify for the main race. After the race, when she is back with the others, it seems people are laughing at her. It turns out her butt, when pressed against the car’s back window, got burned… except where it touched the lettering of the car owner’s shop’s name.
In the end Maaya became sixth in her main race. Ikamasa has his race on the second day of the tournament. The others find him trying to find people to play mahjong with, which causes Momoko to scold him. He angrily tells her he wants to play to improve his concentration. As they argue two guys walk into some of his tiles. Noticing Ikamasa is from Umishou they start talking trash about Umishou, angering the others. But Ikamasa seems oblivious to their comments. When Kaname escorts him to his race he does not seem tense at all and Sanae comments he has always been like that and is most likely the one that has most fun out of all of them. At poolside Ikamasa and Kaname run into the two guys from before and recognizing him they start talking trash again. Kaname wants to retort, but Ikamasa stops him and promises to show them what he can really do. As he gets ready, of course wearing his Speedos with his face on them, everyone starts laughing at his appearance, angering Momoko. She is especially angry because he did not react to the two guys earlier, but Kaname tells her Ikamasa wants to take revenge in the race. During his race he not only beats both guys, but qualified for the finals as well. Despite this he is disappointed, since he was unable to show them his ‘sleeping’. Later that day he finished last in the finals.
On the evening of the second day Amuro is all fired up, since she will have her 100 m freestyle race the next day. Momoko, on the other hand, is very tense. Sanae tells her to relax and tells the others Momoko is always tense before a big event. The other girls, trying to help, offer her to wash her swimsuit. A bit later Momoko and Sanae walk down the beach and talk about how the second and first years all have grown. Momoko tells Sanae she is already satisfied with what she has achieved the last three years and is ready to retire after the tournament. When they return they find Momoko’s swimsuit all clean… and full of tears and holes. As Momoko scolds the other girls, Sanae wonders how much they have really grown.
On the third day Momoko and Amuro prepare for the 100 m freestyle. Since her swimsuit got destroyed, Momoko has borrowed Mirei’s, expecting it to fit… sort of, in most areas. On their way to the pool they run into Ikamasa’s brother Taku, who is very happy to see her. Getting deluded he tells her even if she has lost it will be fine if she will live with him. Momoko, shocked, pushes him away and Sanae congratulates him for his courage. Makio comments it almost looked like they kissed, to which Amuro replies that she and Kaname did kiss, shocking the others. As Kaname tries to cover it up, Momoko and Amuro get ready for their race, with Taku cheering on Momoko. They both have a good start and take the lead, but Momoko feels something is wrong with her leg. After the turning point her speed is off and Kaname notices something is wrong. She struggles to go on, but something happens. Kaname, Makio and Sanae scream at her and, still in the lead, Amuro turns around wondering what happened…