The school's midterm exams have been graded, and Rentarou and the girls are about to get their test results. But first, Rentarou needs to get his phone from the classroom. The classroom is empty except for one girl. Rentarou beckons her outside, but she flatly says she already knows she'll be at the top, triggering a ZING!! when she looks at Rentarou. Despite this soulmate shock, she continues to rebuff Rentarou's suggestions to look at her scores. The boy concedes and regroups with the other three girls. Hakari ranks 25 out of 240, Shizuka ranks 44, Karane ranks 87, and Rentarou ranks 88. Rentarou then sees the top ranked student in the school, Nano Eiai, and asks the other girls if they know her.
Later that day, Rentarou and Nano are paired together in science class, where they have to look at onion cells through a microscope. As Rentarou prepares the experiment, Nano starts copying the textbook diagram into her worksheet, claiming this method to be more efficient than using a microscope. Rentarou's pleas to do the experiment properly only get her to use the microscope to look at the textbook diagram. Rentarou's daze at the school's rumors of her being an android causes him to cut his finger by accident, prompting Nano to lick the cut to clean it. Meanwhile, the other girls are working together on the experiment.
After school, Rentarou tries to get Nano to open up, but she continues to rebuff him on the ground of him being an insignificant part of her routine. But when she gets home, she finds herself swamped with thoughts about Rentarou and is unable to focus on her studies. She tries writing out the decimal expansion of pi, but it only works for a short while before she ends up writing it on every visible surface. The next day at school, she confesses to Rentarou only to try and reject him. But Rentarou, having been rejected 100 times before, knows that she does have true feelings for him, and decides to prove it to her.
Rentarou asks Nano on a date as an opportunity to prove his feelings for her, as well as allowing her a chance to determine if she is justified in rejecting him. They go to an amusement park a few days later, with Nano being befuddled by the attractions there and Rentarou taking pictures with an instant camera. The only time she shows any conspicuous emotions is quaking in fear while riding the Ferris wheel, which quickly prompts Rentarou to comfort her.
Afterward, the two of them look over the pictures Rentarou took during the date, with Nano believing that she gained nothing significant that day. But Rentarou manages to prove that she did gain something significant by trying to burn the photos, prompting Nano to snatch the photos out of his hand. Realizing that there is significance in being happy with the people you love, Nano accepts that she does in fact love Rentarou and agrees to go out with him, following this up by a kiss.
Rentarou introduces Nano to the rest of the girls, reiterating his promise to commit Seppuku if he can't be a good boyfriend to all of them. After talking about his date with Nano, Rentarou offers to take all of them on a date together. At this, Hakari suggests going to an indoor water park, whereupon Karane goes shopping for a new swimsuit after school.
On the day of the outing, Rentarou marvels at the sight of Hakari, Shizuka, and Nano in their swimsuits, while Karane shows up wrapped in a towel, claiming to be feeling chilly. Rentarou and Hakari offer to reschedule the outing, but Karane insists she'll join in once she's warmed up, with Nano suggesting an ideal bench for warming up.
Rentarou and the remaining girls start by going to the lazy river. Shizuka, who is unable to swim, gets swept away by the current, and Nano tries going against the current until Hakari pretends to have the current push her into Rentarou, prompting the two girls to argue over the Buxom Beauty Standard until Rentarou passes out from a Nosebleed.
Hakari and Nano rush him onto dry land and try to perform CPR, only for their efforts to turn into kissing. Meanwhile, Shizuka becomes stranded when her floaty gets punctured on the side wall. Setting off in search of a male staff member, Hakari and Nano are soon confronted by a trio of perverts. Nano inflicts Eye Scream on one of them, prompting his compatriots to become aggressive.
Nano volunteers to spend time with the trio of creepers so that Hakari can search for a male staff member to revive Rentarou. Hakari protests this course of action, but Nano believes that Rentarou cares more deeply for the girls he's known for longer. Hakari intervenes to refuse the creepers' company, provoking an attack that only gets stopped by Rentarou's face. After further arguing, Rentarou kisses Hakari and Nano to prove they're both his girlfriends, prompting the creepers to leave out of disgust.
Karane catches up to the group, explaining that she managed to revive Rentarou by telling him about Hakari and Nano's situation. Rentarou pleads for Nano not to be so reckless in the future, leading her to realize that Hakari was right about Rentarou caring about all of his girlfriends regardless of how long he's known them. Only now does anyone realize that Shizuka is missing, and Rentarou runs off in search of her.
Shizuka's phone runs out of battery, preventing her from signaling for help in the normal way. She sees Rentarou looking for her, and is forced to use her own voice to call out to her. Despite her soft voice in a crowded place, Rentarou manages to hear her and rescues her from the lazy river island.
Regrouping with the rest of the girls, Rentarou quickly deduces that Karane is wearing a towel not because she's chilly but because she's embarrassed. With this in mind, Rentarou strips off her towel while placating her insecurities about her appearance. With everything fully resolved, the pool date resumes in earnest.
Rentarou gets a ZING!! from a girl in the chemistry lab on the way to a pancake buffet with his girlfriends, but gets dragged away before he can identify Girlfriend #5.
The next day after school, Rentarou returns to the lab, finding an 8-year-old girl working on an experiment. The girl introduces herself as Kusuri Yakusen before providing Rentarou a cup of tea. She then prepares a human magnetization drug, which she promptly goads Rentarou to drink.
After forcing him to drink the drug and explaining the side effects after the fact, she drinks a dose of the drug with Reverse Polarity, causing the two to get stuck hugging each other. (If the doses were the same polarity, Kusuri would be upside-down from Rentarou.) Fortunately, the effect only lasts for ten minutes. Unfortunately, Kusuri has to pee. Since she routinely wears diapers to avoid interrupting her experiments, she simply relieves herself right then and there.
After the drug wears off, Kusuri starts going through a list of drugs she invented as Rentarou tries to get his mind back on track. This is when Kusuri reveals that she spiked the tea she served him with a Love Potion due to having fallen in Love at First Sight with him. Rentarou immediately tries to regurgitate the drug, not wanting to accept a confession under the influence of a drug, but his body soon becomes overwhelmed. Kusuri proceeds to administer a neutralizer, having to do so via mouth-to-mouth due to the body spasms.
After Rentarou recovers, the two of them realize that he still thinks Kusuri is cute even after being given the neutralizer, leading her to realize that the Love Potion overwhelmed him due to him already having strong feelings for her. She then confesses while prostrating herself.
Upon standing back up, Kusuri's age has more than doubled, giving her the same appearance as the girl Rentarou saw the day before. She explains that she's actually 18 years old, but a failed attempt at an immortality drug left her with an 8-year-old body that can only be reverted for ten minutes at a time with the neutralizer. (She swallowed some of it while administering it to Rentarou.) Realizing she really is his soulmate, Rentarou returns Kusuri's confession while prostrating himself.
Kusuri is ecstatic about Rentarou accepting her until she realizes she needs to change diapers.
Rentarou introduces Kusuri to the rest of the harem, with Kusuri gifting the other girls with drugs based on what she heard about them from Rentarou. Karane beats up Rentarou until Kusuri explains that the selection she came up with for her was based on things Rentarou likes about Karane. Hakari gets a "become even sexier" drug, which causes her to literally sweat all of her clothes off, prompting Rentarou to provide her his jersey to cover up. Shizuka gets a drug that gives her rabbit ears, which makes her feel euphoric when Rentarou touches them. Nano gets a hair manipulation drug, which comes with a slight risk of baldness, prompting Nano to dispose of the remaining doses when Rentarou says he loves her hair.
Kusuri provides the group with cookies and tea, but suddenly needs to go to the bathroom. She tells everyone that one of the two thermoses is for Rentarou before leaving. Everyone assumes the big one is for the girls and pour the contents for the girls. When Kusuri returns, she realizes that the girls are drinking the tea from the thermos that would hold up to Rentarou's tough grip and tries to warn the others, but it's too late. Kusuri explains that she intended to spike Rentarou with a drug that would make him want to do nothing but kiss her, and that its effect on women is comparable to being transformed into zombies.
They now have one hour to administer the neutralization drug to all four of them, or they'll be stuck in this state forever.
Rentarou and Kusuri race off for the chemistry lab in order to produce enough neutralization drug for all four of the other girls, who are much faster than normal due to the drug in their systems deactivating their rationality limiters. Kusuri suggests using a skin-burning drug to slow them down, but she accidentally splashes the vice principal, shocking Kusuri when she finds that the drug only caused the vice principal's makeup to melt off her face.
Nano sends the other girls down different hallways in order to corner Rentarou with a pincer attack. Rentarou responds by having him and Kusuri split up, leaving only Shizuka chasing him. She trips and falls, and Rentarou takes her to the nurse's office. After treating her and getting attacked by her, Rentarou hangs Shizuka onto a coat hanger and sets off in search of the others.
Rentarou is quickly spotted by Hakari and Karane, who use a meteor bullet to take down Rentarou. The two take turns kissing him, but they quickly start fighting over him, leading him to realize their original personalities are still intact. To this end, he presses their lips together, creating a distraction for them and allowing him to make his way to the chemistry lab.
Unfortunately, Nano is in the chem lab, forcing him to run and hide in a nearby locker. As Nano begins searching for Rentarou, he hopes that Kusuri was able to reach the lab and start making the neutralization drug.
But then he finds Kusuri hiding in the same locker as him.
Kusuri explains that Nano had followed her into the lab, having realized that Kusuri was helping Rentarou, and Rentarou can't make a break for the lab without giving away Kusuri's position. Kusuri laments how her obsession with drugs led to the rest of the chemistry club abandoning her in the past and resolves to stop making drugs.
Suddenly, Kusuri remembers that she has a dose of the neutralization drug on her person. Rentarou thinks she's planning to use the dose on Nano so they can return to the lab unhindered, but Kusuri drinks it herself to revert to her adult body, hoping that Nano wouldn't recognize her. This mixup causes the drug to be spilled before Kusuri can finish it, so the effect won't last as long.
Kusuri emerges from the locker and initially manages to escape Nano's attention. But she promptly gives herself away when she refers to herself in third person and gets tied up with the rope she planned to use on Nano. At this, Rentarou bursts out of the locker and makes a mad dash for the lab, getting caught by Nano in a storage closet.
Just then, Kusuri arrives and administers a neutralizer to Nano, having escaped her bonds when her neutralizer wore off. With Nano saved, Rentarou and Kusuri head off to make batches for the other girls.
After the girls awake from their bender, and Hakari and Karane bashfully claim not to remember anything from the escapade, Kusuri apologizes for the whole mishap. Rentarou explains that while she did start the whole thing, she was still able to fix her mistake. As such, Rentarou promises to continue to love Kusuri even if she continues making drugs, and resolves to help her clean up any messes made in her wake.
Kusuri thanks Rentarou and reaffirms her love for him and her drugs.
Hakari invites Rentarou and the girls to a park hosting a monthly bouquet toss. Whoever catches the bouquet will get a picture with their lover dressed in wedding apparel. The group decides to participate, with Hakari having wanted to wear the special dress since she was a child.
Also participating in the bouquet toss is the Gorira Alliance, a Japanese motorcycle gang formed in the early 21st century. With this in mind, Hakari proposes working together and deciding the winning girl after the bouquet toss is over, and so Rentarou christens his group "Rentarou's Family".
Shizuka is asked to stand on the sidelines to avoid getting hurt, and Kusuri drinks the neutralization drug to age herself up for the bouquet toss, which is being launched by the vice principal.
With the bouquet in motion, the Goriras begin throwing each other at the other contestants, covering up their actions as "training". Karane steals one of their capes so she can join the group and fight them off. In response, the Alliance unleashes a gust of wind that blasts Shizuka into the air, allowing her to catch the bouquet. But in doing so, she loses her grip on the towel that was acting like a parachute and falls to the ground, with her fall broken first by Nano, Hakari, and Kusuri's busts, and then by Rentarou diving across the walkway.
With her team's victory secured, Hakari presents the group with a fistful of chopsticks to decide who should go with Rentarou to the photo stand, intending to cheat her way there by having Nano pick first and then Hakari after that. Nano, however, suggests they all draw at the same time, and Hakari gets the winning chopstick anyway. Kusuri whines about wanting her picture taken with Rentarou, and after some discussions, everyone gathers for a group photo with Hakari in the dress.
Hakari thanks Rentarou for the picture, saying she's finally been able to live out her childhood fantasy.
And then she asks Rentarou to break up with her.
Hakari calls everyone up to the roof for a shadow game for the bonus chapter, where Rentarou has to guess who each girl is by feeling their chests. Rentarou, however, refuses to play and goes home. This leaves Karane to play in his place, with the added penalty of having to be fondled if she guesses anyone wrong.
She succeeds in guessing Shizuka and Hakari, but because Kusuri took the neutralizer without Karane's knowledge, she ends up getting fondled by the other girls in the end.
- Animated Outtakes: The Hakari Meteor Bullet didn’t work out the first time.
- Arson, Murder, and Jaywalking: Played with - the end of Chapter 8 sums the situation up thus:Hakari and Nano are in a whole lot of trouble thanks to some trashy men...!! Shizuka is stranded...!! Karane is complaining about feeling oddly chilly...! And Rentarou is knocking on Death's door...!!
- Batman Gambit: Hakari tries to rig the chopstick lottery by having Nano pick the first chopstick, knowing that when subjected to games involving random selection, she always picks the choice closest to her. This time, however, Nano decides to have all the girls choose at once. But Hakari still gets the winning chopstick anyway.
- Berserk Button: Rentarou is NOT happy to hear the creepers call Hakari and Nano shameless.
- Bitch Slap: Karane gives Rentarou several after he pulls off her towel.
- Blatant Lies: Karane insists that she's wearing a towel because she's chilly, even though (as Rentarou points out) a chilly person would not have ordered a melon soda float.
- Bound and Gagged: Kusuri gets tied up and gagged by Nano.
- Breaking the Fourth Wall: The last panel of Chapter 13 assures the reader that the story will continue a little longer.
- Brick Joke: The guy who had his eyes poked in by Nano in Chapter 8 still has his eyes poked in.
- Call-Back: Rentarou's Imagine Spot has Nano claim that saliva has anti-bacterial properties, just as she did in the previous chapter.
- Catch a Falling Star: After bouncing off the chests of Nano, Hakari, and Adult!Kusuri, Shizuka is caught by Rentarou before she hits the ground.
- Catchphrase Interruptus: Kusuri doesn’t wait for Rentarou to finish his catchphrase before introducing herself to the other girls.
- Comically Missing the Point: Kusuri is more concerned that her drugs can be blocked by makeup than she is about the sight of the Vice Principal's makeup melting off her face.
- "Could Have Avoided This!" Plot: Rentarou tells Kusuri that she didn’t need to drug him to get him to kiss her.
- Deadpan Snarker: Karane's response to Rentarou telling the girls that Kusuri hasn't done meth yet is a sarcastic "Gee, what a convincing way to put our minds at ease."
- Does This Remind You of Anything?: Kusuri mentions that if she and Rentarou drank the same polarity dose of the magnetization drug, they would be stuck upside down from one another and would get chewed out for it, since the manga isn't 18+.
- Do Wrong, Right: Nano's response to Rentarou vowing to kill himself if he can't make all the girls happy is to tell him that ingesting poison would be a more efficient way of committing suicide.
- Drawing Straws: Hakari and the girls use breakable chopsticks to decide who gets to wear the dress for the photo shoot.
- Early-Bird Cameo: Hakari's mother can be seen in Hakari's flashback.
- "Eureka!" Moment: Rentarou has one when he realises that Hakari and Karane are still the same even after becoming zombies, and uses this to get them to kiss each other and escape while they're distracted.
- Explain, Explain... Oh, Crap!: After being given the neutralization drug, Hakari claims that she and Karane can't remember anything that happened while they were under the drug's effects. Karane starts to protest that she does remember everything...then remembers that she kissed Hakari, and immediately retracts her previous statements.
- Eye Pop:
- Karane does one when she learns that Kusuri is actually eighteen.
- Kusuri does one when she realises that the girls are drinking the tea she put in the thermos meant for Rentarou.
- Rentarou does one when he sees what the effects of the drug actually are.
- He does another one when he sees Kusuri drinking the neutralization drug.
- Fake-Out Fade-Out: After Rentarou is caught and kissed by Nano, an ending caption appears. The bottom of the caption, however, mentions the next page and asks what the results of the never-ending kiss will be.
- Fastball Special: Hakari and Karane pull off one while pursing Rentarou, with Hakari as the person being thrown.
- Ferris Wheel Date Moment: Rentarou and Nano ride the Ferris wheel together during their date.
- Finger-Suck Healing: Nano performs this on Rentarou after he accidentally cuts his finger.
- For Want Of A Nail: If Rentarou had not forgotten his phone, he would not have met Nano (at least not immediately).
- Girl on Girl Is Hot: Rentarou is so awed by watching Hakari and Karane kiss that he briefly forgets to escape.
- Graceful Loser: Zigzagged. Karane thanks the Head Gorira for duking it out with her during the bouquet toss, relieved that she wasn’t trying to catch Shizuka with the other girls.
- Heroic Sacrifice: Nano attempts to perform a non-lethal one by hanging out with the creepers so that Hakari can get help for Rentarou.
- Imagine Spot:
- In Chapter 7, Rentarou has one of Nano licking his handkerchief. (It Makes Sense in Context.)
- In Chapter 10, Rentarou has one of Nano copying Kusuri's Verbal Tic.
- I'm Crying, but I Don't Know Why: After stopping Rentarou from burning the photos he took on the date, Nano starts crying and doesn't understand why she's doing so.
- Intelligence Equals Isolation: Implied with Nano. The way she reacts to the attractions, you'd be forgiven for thinking she'd never heard of amusement parks at all before this chapter.
- Intimate Healing: Kusuri has to administer the neutralizer to Rentarou via mouth to mouth due to his body spasms.
- It's All My Fault: Kusuri yells this almost word-for-word once the other girls have been given the neutralization drug.
- Kiss of Life: Hakari and Nano try to do this to Rentarou, but fail.
- Loophole Abuse:
- The Gorira Alliance use each other as battering rams during the bouquet toss, covering up their actions as training. Karane responds by stealing a cape and joining the alliance so she can fight them off.
- Kusuri gets away with taking the neutralizer during the Guess That Breast game because Hakari claims that her "default" child form is her being drugged by the immortality drug.
- Love Potion: Kusuri gives Rentarou one in a cup of tea. He proceeds to vomit it out when he learns about it.
- Oh, Crap!:
- Hakari and Nano have this reaction to seeing Rentarou floating face down in a pool of blood.
- This is Shizuka's reaction to being unable to reach the side of the pool, then getting stranded.
- Rentarou's reaction when he realises that Shizuka might have been drifting along the river all this time.
- Kusuri's reaction when she realises what the girls are drinking.
- Rentarou has this reaction twice in a row - first when he sees Nano in the chem lab, then when he realises that Kusuri is in the locker with him.
- Kusuri's reaction when she realises that she didn't have to drink the neutralization drug and turn back into her 18-year-old self - she could have just given it to Nano.
- Poor Communication Kills: The entire plot of Chapters 11, 12, and 13 could have been avoided if Kusuri had been more specific about which flask was meant for Rentarou.
- Room Full of Crazy: By the time Nano realizes that writing out the decimal expansion of pi isn’t helping her regain focus, every visible surface in her room is covered in numbers.
- School Swimsuit: Shizuka wears one at the pool.
- Shout-Out:
- Rentarou mentions Resident Evil while in the infirmary with Shizuka in Chapter 12.
- Kusuri also mentions Resident Evil in Chapter 13.
- Something Only They Would Say: Kusuri inadvertently reveals her true identity to Nano by referring to herself in the third person.
- Spit Take: Karane does one when Rentarou mentions that she was looking at Hakari and Nano's boobs a lot.
- Title Drop: At the end of the chapter, Kusuri tells Rentarou that she really, really, really, really, really loves him and drugs.
- Too Clever by Half: Hakari rigs a breakable chopstick under the assumption Nano will take the closest one on the grounds of being more efficient, only for Nano to say the most efficient course of action is to all draw at the same time.
- Wham Line: Hakari gives us a doozy:"Rentarou-kun... would you... please break up with me?"
- What Is This Feeling?: Nano asks herself this when she finds herself losing focus due to having fallen in love with Rentarou.
