After preparations for the Kantou region tournament, the Umishou team moves to an inn near the tournament, where they meet the team from Shinomiya University High School again. Tired out because of a competition against Shinomiya at the inn, the Umishou members have a terrible first day at the tournament, but they manage to recover on day two, where the team of Maaya, Sanae, Mirei and Momoko won the medley relay preliminary race against the Shindou quadruplets from Tamatsuka High School. Despite a bad performance during the finals, the medley relay team manages to qualify for the upcoming Inter-high tournament. Amuro, Maaya, Momoko and Ikamasa manage to qualify for their own events as well. Since the Inter-high tournament will be held on Okinawa, after the summer holidays those qualified for it move to Amuro’s home near Okinawa.
It is ten days before the Kantou region tournament and Momoko, not satisfied with the qualified members’ performance, wonders if there is a training method that can help them in such a short timeframe. After hearing Ikamasa’s plans for training, the best one involving a special powered suit, called Moro1, Kaname thinks of a method Momoko likes: tying a rubber cord around your waist and the other end to the pool wall. Momoko orders Ikamasa to get them some rubber cords and soon Ikamasa returns, bringing a few dubious looking ones (they lack belts and some seem to be used) and those qualified for the tournament prepare for training with them. Momoko nearly reaches the far end of the pool when she spots Amuro struggling in the next lane. Despite the rubber being stretched all the way, she wants to go on, despite Momoko’s warnings. When she gets tired, she is catapulted back to the start and is about to hit the pool’s wall when Kaname pushes Takeda into the water to absorb the crash. Training continues without further problems and when everyone is about to go home, those (including Momoko) that rode their bicycle to school, find their inner tubes missing. Because Ikamasa is the obvious culprit, Momoko decides Ikamasa has to pretend to be a horse and carry her home.
Five days before the Kantou tournament Makio and Amuro comment about the training being lighter than the previous weeks, but Maaya tells them this is normal practice right before a tournament. Momoko agrees and tells them it is the best time for mental training. For this Ikamasa takes them to a temple, run by a regular at the Ikariya restaurant, for Zen meditation. Oka, the head priest, orders them to clean the temple grounds, dressed in swimsuits, which, he claims, is part of their training. The meditation session, still in swimsuits, starts after they have finished cleaning. As everyone sits still, Oka moves around, ready to tap on the shoulder whoever lacks concentration. Amuro keeps looking at him, smiling, and when he taps her, she cheers for being tapped first and bends over, wanting to get smacked on her bottom as well. Oka decides to ignore her and when he moves on he spots Maaya playing with her cell phone. He complains to Ikamasa, also telling him he is new to Zen meditation, but Ikamasa tells him to just make it look good. Momoko overheard them and decides to take over, telling Oka to sit down and shut up and kicking out Ikamasa. After beating up a sleeping Takeda, she notices Amuro is gone. Amuro soon returns, holding her own whacking stick, which turns out to be a grave post. While dodging an angry Momoko’s stick, she accidentally breaks a 2 million yen vase. To pay for it, the swimming club has to do beggar training outside the railway station nearest to the temple, still dressed in their swimsuits of course.
The day before the Kantou tournament the Umishou team is on their way to an inn near the tournament’s site. Momoko forced Oka, the head priest, to arrange transportation for them, because he fooled them, so he lent them a kindergarten bus, which is being driven by Masashi. Of course, such a trip is eventful, as Ikamasa insists on playing games, Maaya needs attention, Mirei is getting carsick and several others need to go to the toilet. When more and more people complain they need a stop, Momoko decides to take a ten minute break. With everyone back in the bus, they continue their journey. When Kaname sits next to Momoko to go over the schedules, Momoko acts nervous and reacts to every bump in the road. Suddenly Makio runs towards them in panic, telling them they left behind Amuro. She finds Momoko clinging to Kaname and assumes Momoko is after Kaname and has left behind Amuro on purpose. More and more people start telling Momoko to turn the bus around to pick up Amuro, but she tells them they are almost at the inn. She desperately wants to reach the inn, because she has to use the toilet; during the stop she was too busy policing the others. Meanwhile, Amuro is waiting patiently in front of the store where they had their stop, wondering where everyone else is.
The night before the Kantou tournament the Umishou team arrives at the inn near the tournament’s site. In the end they did turn around to pick up Amuro (and Momoko used the toilet at the store). After dinner they decide to visit the inn’s outdoor baths. While the girls are enjoying the bath, Amuro notices Mirei is missing. Mirei, wanting to change by herself, hears people approaching the changing room. It turns out to be Shinomiya’s swimming team, who are staying at the inn as well. They realize the Umishou girls are staying at the same inn and are having a bath and say they want payback. Mirei tries to sneak out, but fails. Just when the Umishou girls want to leave the bath, Karena and the other Shinomiya girls enter the bath, challenging them to a competition. When Momoko declines, Karena threatens to shave a captured Mirei’s nether regions.
As the boys, in their own bath, wonder what is going on in the girls’ bath, the Umishou and Shinomiya girls try to agree on the type of competition. In the end an endurance competition is chosen and as Sanae is the first to drop out, Karena tells them the losers will have to shave their nether regions in front of the winners. As people start to drop out, including Karena, after making sure Tomoko and Miyuki Hara can continue. As more and more girls drop out, on the other side of the wooden fence Ikamasa gets more and more restless after hearing something about shaving. When he crashes down the fence all Umishou girls panic and stand up while covering themselves. As Karena declares Shinomiya the winner, Makio realizes Mirei is missing again. She turns out to be still in the bath, floating on her belly half unconscious and too afraid to get out, which makes Umishou the winner after all.
The first day of the Kantou tournament turns out to be disastrous for the Umishou team; none of the three participants, Amuro (50 m freestyle), Keiko (800 m freestyle) and Maaya (100 m backstroke) all fail in the preliminary rounds. It turns out everyone is still dizzy from the previous night’s endurance competition against Shinomiya. The second day, besides Mirei’s 200 m individual medley and Sanae’s 100 m breaststroke, also features the medley relay, for which Umishou’s team will be Maaya, Sanae, Mirei and Momoko. Momoko marks this as their chance to beat Shinomiya. Maaya, though, not being used to losing seems really down after her terrible race. Momoko tells her to just forget about it, but Maaya angrily runs away. Kaname, Ikamasa and Takeda go after her and Momoko tells everyone else to go to bed to get rested. Kaname’s group completely misses Maaya, who is sitting in the high grass near the river, but she is found by Mirei, who not able to sleep, decided to take a walk. Maaya tries to argue with her and ends up crying against Mirei’s chest. Mirei manages to calm her down and the girls promise to do their best tomorrow. By then Kaname’s group have found Maaya as well and Maaya beats Ikamasa for daring to watch them (he was nearest to her).
On the second day Umishou is waiting on the gallery for the day’s events to start. An overexcited and completely recovered Amuro notices a group of students all looking and dressed the same, kind of looking like a choir, next to them. Kaname tells her they are from Tamatsuka High School, a very strict music school, whose team will also perform in the medley relay. Amuro runs over for a closer look and meets one of their swimmers, Nagi Shindou, who appears to know a lot about Amuro, because, she says, Amuro is her type. Meanwhile Maaya is training in the pool, all fired up, and tells Momoko, Mirei and Sanae to join her. Amuro appears and jumps into the pool as well, colliding with a swimmer who appears to be Nagi, but for some reason is very shy. Amuro goes after her and runs into ‘Nagi’, who is on the phone. As Momoko and the others catch up with a confused Amuro, a girl, again looking like Nagi, runs into Amuro, apologizes to her and runs away, confusing her even more. At the start of the relay medley, Maaya, Sanae, Mirei and Momoko are ready. In the lane next to them Nagi and three other girls still in robes are announced. When they remove their robes the Tamatsuka team turns out to consist of quadruplets.
The medley relay event starts with Maaya for Umishou and Mimi Shindou, the shy sister, for Tamatsuka. Meanwhile, on the balcony Kaname notices the Tamatsuka students form a choir and start singing. Maaya is in the lead, but Mimi, who is in fifth position, speeds up, getting into second place while moving in perfect harmony to the song’s rhythm. By the time they have to switch, Mimi has caught up to Maaya and both finish in the same time, 0.02 seconds from a new high school record. Next up are Sanae and the timid Mayo Shindou. Despite giving it her all, Sanae is unable to match Mayo’s speed. Ikamasa, realizing the effect of the Tamatsuka choir, tells the other Umishou students to start singing as well. Amuro follows his example, but of course, both sing a different song. Meanwhile, waiting for her turn, Mirei worries about losing, but Maaya encourages her, having Momoko wonder when their teamwork got this good. By now Tamatsuka has their second switch with Ai Shindou starting and two seconds later Sanae finished, sending Mirei on her way, trying to catch up.
Mirei managed to catch up to Ai and now it is up to Nagi and Momoko to decide the winner. Momoko’s start is a bit slow and as she catches up Ikamasa strips to his underwear and starts singing the Onoshima dance song and with most of the others joining in they dance towards the Tamatsuka choir, causing a disturbance amongst its members. Momoko, noticing Nagi, missing the help from the choir, slowed down, realizes this is her chance and speeds up, managing to finish 0.07 seconds before Nagi, handing Umishou the victory. Ikamasa, who now lost his underpants as well, joins in the celebrations, but is soon carried out of the venue for indecent behavior. Despite their big victory during the preliminaries, in the finals Umishou failed to end in the top 3 and neither Sanae nor Mirei managed to win their races later that afternoon; they had used up all their energy during the preliminaries. Momoko is disappointed they failed to qualify for the Inter-high tournament, but Kaname arrives and tells her the relay medley team did qualify, due to their performance during the preliminaries, which counts as well. The next day Amuro wins the 100 m freestyle, with Momoko in second and Karena in third place.
After the Kantou tournament at the start of the summer holidays the Ninagawas are still staying at the Okiuras’ house. When Masashi comments there is a watermelon eating competition at the beach, Amuro decides to participate, dragging Kaname along with her. Masashi decides to participate as well. Waiting for the starting signal, Kaname wonders why they have to wear swimsuits when the rules are explained: whoever eats slower than a slice a minute or has to throw up finds a hatch in the floor underneath him or her opening, sending him/her into a water tank. Kaname realizes he has to win and starts eating. One by one contestants drop out (literally) until Kaname, Masashi and Amuro remain. After Amuro drops out as well, Kaname asks Masashi to let him win because he cannot swim, but Masashi refuses. After some more time, Kaname and the referee notice Masashi has fainted, making Kaname the winner. The next day Amuro brings Kaname a large plate of watermelon slices, demanding a rematch.
Some time after the Kantou tournament, in which six people qualified for four different events at the Inter-high tournament (200 m backstroke: Maaya, 100 m freestyle: Amuro and Momoko, medley relay: Maaya, Sanae, Mirei and Momoko, and 200 m butterfly: Ikamasa), Ikamasa is demonstrating an upgraded Moro1-X training suit when Kaname arrives with big news. Later that afternoon people from Swimming Magazine will arrive for an interview and to take pictures. Not wanting to have any embarrassing pictures taken, Momoko decides they need some pose rehearsals. Because Maaya has modeling experience, she decides to help them out with their poses. When the magazine people arrive and decide to start with taking pictures, the six members going to Inter-high take their rehearsed poses. The reporters think it looks unnatural and in the end they take a normal group picture, before moving on to their next location.
On a hot day while taking Lala, the Okiura’s dog, for a walk, Kaname and Amuro run into Makio and her 9 year old cousin Kiyoharu (Kiyo) Saka, who are catching insects. Kiyo complains they are only catching cicadas; he wants to catch something bigger, like a beetle. When Makio promises to catch him a beetle, Amuro tells her those will not be out until it is dark. After telling Kiyo she will catch him a beetle at night, Makio begs Kaname and Amuro to tag along with them. That night, after some preparations, Makio has caught some bugs, but Kiyo complains they are too small. A larger beetle lands on Amuro’s head, but before they can catch it, she scares it off and Kiyo complains they are useless, not wanting to go home before catching a big one. One by one they fall asleep, but Makio accidentally kicks over a bucket with some fluid to lure in insects. A bit later, Kiyo is awakened by the sound of insects and finds a large beetle sitting on his chest. He feels something prickly all over him and looking better, it turns out he is covered in beetles. His screaming awakens Makio, just in time for her to have a laugh and then see him pass out in fear when he sees a shadowy figure shaped like a very large beetle, which turns out to be Amuro with a branch caught in her hair. The next day, when the four of them visit the beach, Kiyo seems to have developed a fear of insects.
Momoko is waiting for Sanae, who appears 30 minutes late. As they celebrate making it to the Inter-high tournament, Sanae says they have one thing left to do that summer, getting boyfriends. When two guys enter the restaurant they are in and take a nearby table, Sanae decides she and Momoko should join them. The guys turn out to be college students and Sanae uses her lying skills again. After finishing eating, the four of them go for karaoke, but Momoko gets more and more annoyed by Sanae’s behavior. As Sanae tries to impress the guys, the guys, admitting they are not that good at karaoke, get into a conversation with Momoko. It turns out they have swum in the past as well and soon they are talking about swimming, when Sanae notices that not she, but Momoko gets all of the guys’ attention. She decides to try to get their attention by stripping and when Momoko asks her what she is doing, she angrily replies that Momoko was trying to get ahead of her and ignored her passionate performance. Momoko, getting angry as well, reacts that she gave up her relaxation time to hang out with her and soon the girls start fighting each other. The next day during training both are still in a foul mood.
Mirei finds enough courage to buy the penis sheath she found in a shop. Exiting the shop, carrying a bag containing the large object, she runs into the two members from the school newspaper, who had run an article on the swimming club after their successful performance at the Prefectural tournament. When she refuses to tell them what she just bought, they get suspicious and since they have some free time, they decide to follow her. Mirei, realizing she is being followed, manages to shake them by entering a very narrow space between two buildings. But when she wants to exit it after the newspaper duo left, she realizes she got stuck. She manages to move a bit, but by doing so she rips her clothes and manages to get the bag stuck. Not wanting to lose the bag and its contents, she stops moving. When it gets dark a dog finds her and when it starts humping her leg, she panics and manages to squeeze her way out of the narrow space straight into some bright light. She thinks it must be the newspaper duo and in her mind she already sees a photo of her in her ripped clothes in the school newspaper, but the person holding the light turns out to be Ikamasa, who is out cutting plants for food replacement at his family’s restaurant. Calmed down, Mirei realizes the dog ran off with her shopping bag and her newly acquired penis sheath.
When Momoko reminds everyone that this year the Inter-high tournament is held on Okinawa, Amuro offers them to stay at her home on Okinawa. Momoko thinks it is a good idea for the members participating in the tournament. The others should go later and directly to the tournament’s venue. So a week before the Inter-high tournament Momoko, Sanae, Maaya Mirei and Ikamasa, together with Kaname and Makio as support, arrive at Okinawa. Amuro, who has travelled ahead of them to make preparations, left Kaname, who has been to Okinawa once when he was a kid, some directions to her house. Following the directions they arrive at a port, where an old man is waiting for them. He tells them to get aboard his boat and soon they depart, moving further and further towards the east. After a long journey, during which the Umishou members start to fear they are captured by pirates, they finally arrive at an island’s huge cliff. Before they know it, their boat is pulled out of the water by a crane and on the shore on top of the cliff they are welcomed by Amuro and her family. It turns out their house is on the Daito Islands, 217 miles to the east of Okinawa.