Characters / Grand Blue

Peek-a-Boo

An inter-collegiate scuba diving club composed of students from Izu University and Oumi Women's University in the city of Izu in Shizuoka Prefecture, Peek-a-Boo, or PaB for short, uses the titular "Grand Blue" diving goods shop as their meeting place for club activities and the main source for equipment and diving services... when they're not busy partying hard, getting absolutely smashed, and/or running around in varying states of undress.

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As a Club

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• A Day in the Limelight: Chapter 84 is mostly a flashback for the upperclasmen as well as minor PaB, Azuma, before he joined the club.
• Artistic License – Biology: Considering the amount of booze they drink, as well as the cartoonishly outrageous alcohol content of some of the drinks they consume, it's surprising that the members of PaB still have their livers intact and haven't landed at the hospital numerous times... or landed at their graves, for that matter.
• Badass Armfold: Kotobuki and Tokita tend to fold their arms every now and then while talking.
• Bunny-Ears Lawyer: The seniors may spend their time drinking and partying, but when it comes to anything related to actual diving, they are pretty good at it.
• Cloud Cuckoo Lander: The entire club is insane with the male half being nudist alcoholics and even the sanest member having an extreme obsession with the ocean.
• The Corrupter: Played for Laughs with the club's influence on Iori and Kohei, who were initially weirded out by their seniors' tendencies, but have since begun to participate. It's implied their tolerance for alcohol has also increased because of how much they've had to drink since joining the club. It also crosses over into Corrupt the Cutie territory when Aina joins in.
• Embarrassing Cover Up: Turns out, there's a reason why Peek-A-Boo has free rein on their antics at their college campus. Ushironomiya pushed an assignment so outrageous at a student 1½ years back that the latter locked himself at a classroom and threatened to harm himself and others with a bottle of acid. In an attempt to cover it up, Ushironomiya sends Tokita and Kotobuki to defuse the situation by rendering the student drunk beyond aggression alongside Asuza (who happened to be passed out at the room without anyone noticing). However, Ushironomiya is caught by the school's admins. The incident was so bad for the school, as the whole situation was Ushironomiya's fault, that the admins had to publically commend Peek-A-Boo as an exemplary club in order to cover up the whole incident.
• Enraged by Idiocy: Chisa and Aina will react with scorn whenever Peek-A-Boo starts with their usual antics.
• Everyone Has Standards:
  • Despite the abundant alcohol consumption, frequent nudity and sex discussions, the club is disturbed by Nanaka's unhealthy affection for Chisa.
  • Sure, they're party animals, but when when it comes to diving, that's no time for jokes. The seniors always make sure to let their underclassmen know that even when it's beautiful, being underwater and making a mistake there could escalate into something dangerous.
  • For all their raunchy behavior, the boys make it a point to never let any creep come even remotely close to any of the girls. Even the tiniest bit of ill intent is bound to invite their righteous wrath.
• Heterosexual Life-Partners: Kotobuki and Toki are always together and get along well.
• Home Nudist: The guys of the diving club Peek-a-Boo frequently get naked not even caring if girls or visitors are present and will even go Streaking outside when chasing after someone.
• The Leader: Kotobuki and Tokita are the co-leaders of the club.
• Meaningful Name: "Peek-a-Boo" is a not-so-subtle nod to the nudism rampant with its male majority; even its portmanteau name "PaB" may be read as "pub", befitting its culture of alcoholism.
• Naked People Are Funny: A major Running Gag throughout the series is the boys' tendency to run around in varying states of undress, so much, that they somehow incorporate nudity in completely unrelated situations, and it somehow has bled outside the activities of the club to the point of exhibiting nonchalant exhibitionism outside common societal norms.
• Noodle Incident: Kotobuki, Tokita, Asuza and Nanaka apparently have a shared romantic past that got messy. Their relationships as of the current time are a result of them amicably breaking off whatever romantic liaisons they had for one another for the sake of their friendship. Though it seems to be resolved, some hints are given to indicate that there's still lingering feelings out there.
• The Pirates Who Don't Do Anything: Despite its ostensible activities, most members of Peek-a-Boo spend more time drinking, playing games, and walking around half- or fully naked. It's a shock for Iori and Kohei when the club actually does something diving-related.
• Situational Sociability: Played with. The members of Peek-A-Boo tend to behave better around strangers... however, give them a little confidence and they'll be naked in 5 seconds tops.
• Sleeps in the Nude: In addition to being Home Nudists the guys of Peek-a-Boo will fall asleep on the floor while still being nude with not even a blanket covering them.
• This Is Wrong on So Many Levels!: Outsiders are often bewildered at the club's sheer alcoholism, and how much it comes up whenever they interact with a club member (usually Iori or Kohei).
• Those Two Guys: Kotobuki and Tokita are usually seen together.
• Took a Level in Badass: At least in terms of alcohol tolerance, Iori and Kohei probably had average tolerance for men their age before joining the club but they're now monsters who are so used to drinking Spirytus with it's 96% alcohol content that it goes down like water for them.
• Trademark Favorite Food: In this case; drink, which is anything alcoholic. The two most famous among these are "oolong tea"^note 90% vodka + 10% whiskey and "water"^note actually vodka. The club also loves to drink Spirytus because of it's 96% alcohol content.
• True Companions:
  • Despite their vastly differing personalities and frequent loggerheads, the members of Peek-a-Boo share a great chemistry and teamwork forged through college life, drinking sessions, and the fact that scuba diving is an activity where safety is of paramount importance, and thus is best done as a team. During the Okinawa trip Aina even contemplates on how much of an improvement Peek-a-Boo is, quirks and all, compared to her former club, the Tinkerbell tennis team, where everyone else, even Captain Kudou, shunned her for her awkward attempts at socialization.
  • It's stated by Azusa that to achieve the level of mutual trust that they show among themselves, the three main senpai and Nanaka had a long story between them before the kouhai came into the fold. As Asuza states, it's not like they were sitting on their hands the whole time... and if her words are to be taken at face value, there was some saucy stuff.
• Walking Shirtless Scene: Pretty much the male portion of Peek-A-Boo in nearly every scene they're in plus no pants; Azusa also regularly walks around without a shirt, wearing just a bra to cover her top.
• Weirdness Censor: Through the gang's alcohol-fueled binges and tendency to walk around naked, Nanaka's crush on Chisa is considered the weirdest thing about their group.

The First-Years

Iori Kitahara

Voiced by: Yūma Uchida
Portrayed by: Ryo Ryusei

A freshman who has moved to Izu to attend its university's mechanical engineering program, Iori moves in with his uncle Toshio Kotegawa and cousins Nanaka and Chisa, only to get roped into Peek-a-Boo (despite his initial lack of swimming skills) which occupy the Kotegawas' family-run diving goods shop "Grand Blue". Procrastinating and somewhat selfish, but a good person nonetheless.

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• Accidental Pervert: Many times towards Chisa. In Chapter 22 he caught her in various compromising positions during an all-girls' party, such as being dared by the girls to wear a sexy two-piece bikini and later being groped by Nanaka and Azusa. And in Chapter 42 he caught her topless while undressing after she fell over the beach in a drunken stupor.
• Adaptation Dye-Job: In the manga, Iori's hair color is a very saturated teal; the anime changes this to a dull blue.
• Attractive Bent-Gender: Of all the primary boys, Iori gets this treatment the most.
  • During the "Boycon" Beauty Contest at the end of Izu University's festival, Iori gets help from Azusa to pose as her in order to humiliate Captain Kudou, who gets played for a fool via an Unsettling Gender-Reveal when he thought "Azusa" accepts his confession after Kohei pulls an earlier one on "her"; Iori ultimately wins the pageant.
  • When forced to work at the maid cafe during the Oumi Festival (alongside Kohei), Iori can pull off a maid outfit and ponytail surprisingly well, at least enough that his first-year engineering friends don't immediately recognize him. They even decide to flirt with him.
• Big Brother Instinct:
  • A flashback of his childhood has Iori finding Shiori after she got lost in the woods. Present day, while their relationship soured a lot since, Iori makes it his priority to defend his little sister from perverts, especially Kohei.
  • When trying to escape Chisa, who is livid at having been seen topless by him, Iori realizes that she stopped chasing and notices a lone shoe next to a ravine. He catches a glimpse of an unconscious person on the bottom, and thinking it's Chisa, he immediately careens down the ravine. He finds that the unconscious person is Kudou, who once regains consciousness, tells Iori that the person he was expecting must have been so dear to Iori that he saw no trouble whatsoever in throwing himself down a ravine for their sake.
  • In Chapter 49, towards the end of his, Chisa and Kohei's trip to his family-run inn (to claim Iori's passport from Shiori so he can join the upcoming Palau trip), realizing that Kohei and two male German otaku try to help him by luring her out using a mobile lolicon hentai game as a playbook, he goes to great lengths to wrestle them away from Shiori, who gives it anyways partly as gratitude to him protecting her, partly to keep him away from Carina, the other perverted German otaku.
• Book Dumb: His grades at college are abysmally bad, and his parents consider him dumb as bricks (though it's implied that they're more upset at him refusing to inherit their inn). As he had the full intention of having a fulfilling college life, it's not quite known how Iori would operate if he wasn't forced by his senpai to binge-drink almost every night.
• Boyfriend Bluff: For Chisa; following the Izu Spring Festival, he's forced to pretend as her boyfriend to make sure she doesn't get unwanted attention, lest he face the wrath of Nanaka for failing to do so. Most of the Izu University boys, especially in mechanical engineering, think the pair are a couple (thus making him a target of their jealousy), but Iori can't do a thing to refute it. He later becomes more tolerant of this, and uses it alongside Chisa as a method to prevent her from getting hit-on.
• Brilliant, but Lazy: It's implied that despite apparently being Book Dumb, his grades are bad because he is out drinking with the club every night or doing other dumb stuff with his friends. He can get decent grades if he puts an effort in, and he has also shown several times that he has a keen sense of observation skills.
• Butt-Monkey: Iori receives an awful lot of abuse from almost everyone he interacts with. As a matter of fact, Toki and Kotobuki consider both his antics and dirt-poor decision-making hilarious and highly entertaining.
• Chivalrous Pervert: In spite of the raunchy stuff that he engages into, it's shown that Iori cares a great deal about the happiness of his friends, and whenever stuff would get so heated the girls might be affected, he is the first to put his foot on the ground.
• Clueless Chick-Magnet: He has some Ship Tease with Chisa (despite their more sibling-like dynamic and being cousins by adoption), Aina and Naomi obviously have a crush on him, and Azusa and Sakurako have at least expressed some interest in him. He is not aware of any of them.
• Distracted by the Sexy:
  • Downplayed. During the Okinawa trip, Iori had to sleep elsewhere because the men's room is too small for him, Kohei, Tokita and Kotobuki. Sure enough, he had to spend the first night between Nanaka and Azusa, two of the sexiest girls in the series, which would be a good thing but for the fact that he, Kohei and Aina also had to take up diving licensure exams the next day. He tries his best to keep himself focused, such as spending the night studying and choking himself unconscious, but his libido ultimately gets the better of him when he miswrites his name as "Boobs" while taking written exams in front of Nanaka, earning him a salvo of slaps across the face from an overlooking Chisa.
  • Invoked. When he lands in an uncomfortable situation with Nanaka which leads her to believe that Iori is attracted to her, Iori states that he does find her stunning, but that this is not the kind of relationship he wants with her, as he considers her among his closest family, almost a sister. This eases Nanaka's worries.
• Disappointed in You: Being who he is and how he behaves, Iori rouses this out of plenty of people:
  • This is the default when it comes to Chisa, who through their interactions makes it more than clear that she expects an awful lot better from Iori than what little he shows her.
  • This happens aplenty when it comes to Aina, who knows him to be a better person than he shows, and has a crush on him due to having a firsthand experience of his better personality traits.
  • Played for Laughs when it comes to Tokita and Kotobuki, who place unrealistic standards on him, especially when it comes to binge-drinking and "club activities" (it doesn't help that Iori isn't as much of a Bunny-Ears Lawyer as the two).
  • His parents consider him a dumbass, though it's implied that they're more upset at him for refusing to inherit their inn.
• The Dreaded: He has an abysmal reputation at college as a nudist pervert... which is only partly true, as it's not entirely his fault. It's not until later in the story that he realizes that his prospects with women are considerably narrower than he thinks due to said reputation.
• Even the Guys Want Him: Not only can Iori rock being an Attractive Bent-Gender, but Naomi is head over heels for Iori, much to Sakurako's chagrin.
• Everyone Has Standards:
  • Despite his mutual antagonism with his little sister Shiori, he still knows better than to leave her alone with Kohei.
  • He tells Sakurako that even though he's not above criticizing and making fun of Kohei for his otaku tendencies, he's never once considered depriving him of what makes him happy or forcing him to become someone he's not.
  • Iori refuses to tolerate messing with someone's fundamental dignity or happiness, so he's very given to exact justified retribution for those wrongs. As a matter of fact, this is the main reason girls like Aina and Sakurako are attracted to him (the former, for protecting her from her former clubmates; the latter, exactly for being criticized over her harsh reaction to Kohei's hobbies).
  • Even beyond the club's standards (as shown in the club's entry of this trope), Iori does not tolerate anyone looking funny at his cousins Chisa and Nanaka, or at Aina and Azusa for that matter. This is not something wise to do with Iori present, as he'll find the most underhanded method available to him to get back at whatever idiot who dares to try.
• Famed In-Story: Downplayed, Chapter 62.5 reveals that Iori is infamous at his college as a huge pervert to the point every girl in his school recoils from disgust the moment he introduces himself.
• Foil: To Chisa. Iori did not want to inherit his parents' inn and fled his family home to live with the Kotegawas and enroll in college, while Chisa had to enroll in college to appease her mother, who disapproves of her dream of becoming a diving instructor, and thus maybe inheriting the family business. As such, Chisa and Iori find themselves sharing the same space and becoming close friends after they came from two completely opposite backgrounds, Iori having been inside and looking out, while Chisa is outside and looking in.
• The Heart: Despite his rotten personality, Iori is a surprisingly good motivator. He makes Aina realize there's no such thing as a "perpetual laughingstock", while he calls out Sakurako's criticism of Kohei's otaku lifestyle when there's more to him than just that and later comforts her after her Love Confession got rejected by Naomi.. On these occasions, his Peek-a-Boo seniors and engineering friends, respectively, follow his lead.
• Heroic Comedic Sociopath: He's not shy about throwing his friends under the bus (so long as it's minor stuff). He's so unapologetically prone to playing dirty that more than once, Sakurako has told him that she absolutely loves that side of him.
• Hidden Depths:
  • Iori has a fairly good hand-eye coordination, allowing him to easily flip Chisa's skirt with nothing but rubber balls and hold his own in a tennis match against the Tinker Bell boys.
  • Though it's overshadowed by his bad grades, poor decision-making and reactionary nature, it's shown that Iori is a deeply kind individual, a reliable friend when things get serious, and a person whose enthusiasm is his greatest asset.
  • Iori used to write songs. They are actually not that bad either, but he finds them incredibly embarrassing. He later admits he would like to form a band and get famous, showing he still enjoys making music.
  • It's shown that Iori very much wants to be the person Chisa expected him to be when he first arrived to Izu, and has manifested through his actions that he really wants to be Chisa's friend. However, the environment they're in caters to the worst side of himself, though in occasion, he has gotten the point across to Chisa. He IS the dear friend and companion Chisa wanted... but he's a party animal too.
  • His dedication to Chisa runs deeper than anyone gives him credit for. When he wins ¥300,000 at the scratch-offs after the trip to Palau, his main priority is to take her to Okinawa and dive together just as he had promised her during their first trip. This proverbially sweeps her off her feet.
• Hoist by His Own Petard: During the Okinawa trip (which also doubled as the freshmen's licensure exams), upon learning from Nanaka that he is risking failure due to his difficulty with goggle-clearing exercises, he tries his best to train in secret for fear of being teased by Kohei and Aina, and gets Chisa (and later Aina) to help submerge him in the backyard pool of their lodging. However, one onlooker mistakes the training for a crime scene, and when a cop shows up, Iori cannot leave the pool after he goes skinny-dipping later that night, causing him to fall ill the next day and miss out on the practical exams which Kohei and Aina pass.
• Hyper-Awareness: Time and time again, Iori has shown that he pays more attention to details than other people. For instance, while he knows he doesn't actually know his sister very well, he can deduce that she also has no intention to inherit their parents' inn and actually wants to be free, like him. He also manages to restore Chisa's strained views on her mother, as he notices that her mother apparently is deaf on her left ear. Iori remembers that Chisa suffers from hurting her ear when diving too long and deduces that her mother is just worried Chisa might end up deaf like her one day. On the other hand, he is quite Oblivious to Love.
• In Vino Veritas: Played with. Iori's party animal tendencies tend to bring out the worst in him, but he's at his most virtuous and truthful when dealing with his closest friends and relatives while sober. It's hidden deep behind the alcohol, but his moral barometer is peerless.
• Irony: Despite his efforts to measure up to Chisa's expectations of him (and apparent failure at it), it's shown that Iori IS already the dear companion Chisa wanted him to be... only that he's an unhinged party animal on top of that. Beggars can't be choosers, after all...
• Jerk with a Heart of Gold: On one hand, most of Iori's motivations aren't entirely for good intentions and can be obnoxious, selfish, unreasonable, and cruel to Kohei, his engineering friends, and Peek-A-Boo members (and vice versa). That said, if a third-party decides to be a dick to his friends, he will go to great lengths to give them what's coming to them, as Kudou and Sakurako found out the hard way. In addition, despite his mutual antipathy with his younger sister, Shiori, he will still act as a good brother to her when the situation calls for it.
• Just Eat Gilligan: In Chapter 59, Iori subjects the participants of a mixer to a lie detector test, where everyone is supposed to state whether they are attracted to someone present. Since it's known that Iori is attracted to Azusa and Nanaka, Sakurako demands an answer excluding these two (with the remaining girls being Aina, Chisa and Sakurako). Iori, believing it's a Morton's Fork, answers that he is attracted to multiple people, as he feared answering "Yes" would lead to him being Mistaken for Gay again. The obvious answer would have been just saying yes and letting everyone believe he's thinking of Chisa, his official girlfriend, whom he already admitted he finds attractive. Admitting that he likes at least one more person other than Chisa outrages Nanaka.
• Kissing Cousins: Played with. Iori finds Chisa and especially Nanaka attractive, but he doesn't view them as anything but his sisters. Not to mention, they are Not Blood Related at all. However, he's closer to Chisa than to any other girl in the story, which makes her a serious prospect.
• Like Brother and Sister: Iori holds Chisa and Nanaka very close to his heart. With the latter, after clearing a few misunderstandings, he clarifies to Nanaka that he regards her as a surrogate Cool Big Sis; with the latter, their relationship is akin to twins who deeply understand each other enough to think alike, such as cooking in tandem and finishing each other's sentences. His closeness with Chisa is one of the reasons Aina considers Chisa a serious prospect for Iori.
• Likes Older Women: By his own admission, Iori finds Azusa and Nanaka more attractive compared to his fellow freshmen Chisa and Aina (not to say that he doesn't consider them pretty too).
• Magnetic Hero: Iori has the tendency to make friends with anyone he spends more time with. His honesty, empathy, tolerance and respect for someone who is serious about their interests is the reason he is immediately liked by Azusa, Kaya Mizuki, Aina, Naomi and even Sakurako.
• Mistaken for Gay: Due to Iori's attempt to appeal to hardcore siscon Nanaka, Azusa thinks Iori is not only bisexual, but also in love with Kohei. He doesn't have the heart to tell her she's wrong after realizing she, who openly identifies as bisexual, is excited over someone who apparently shares the same interests as her.
• Mr. Fanservice: Besides being good-looking, among the Peek-a-Boo boys Iori (as well as Kohei) is frequently seen naked.
• My Greatest Failure: Albeit Iori usually shows little remorse about the outrageous stuff he engages into, the aspect he regrets the most is how hilariously badly he hit off with Chisa. The other stuff is no big deal, but Chisa's approval and friendship is paramount to him, even though he is remarkably bad at showing it.
• Oblivious to Love: Iori is unaware of just how much of a ladykiller he is, having already attracted the attention of Aina, Sakurako, and even Naomi.
• Oh, Crap!: In Chapter 59, during the lie detector game, Iori states that he's attracted to multiple people which triggers Nanaka's Big Sister Instinct.
• Old Shame: In-Universe, Iori wrote several original songs back in middle school and is absolutely embarrassed by them. His sister Shiori not only found them, but also gave Chisa a CD recording of those songs as performed by their father, in order to blackmail Iori into returning home for the summer break
• Pet the Dog: The reason Aina has a crush on Iori, is that he helped her during her most abject time and showed her that there are people who will accept her unconditionally.
• The Runaway: He's the son of a ryokan (a traditional Japanese inn) owner, who was originally meant to succeed the family business, but instead ran away to college, leaving his sister to inherit it.
• Saying Too Much: Iori has a nasty habit of speaking his mind too much, resulting in misunderstandings, primarily with Chisa.
• Throw the Dog a Bone: After failing to earn his professional diver's license during the Okinawa trip when he went down with a fever on the day Kohei and Aina took their exams, he finally gets it in Chapter 28, albeit barely and in a simpler, private session made for him on the waters just outside Grand Blue. Moreover, he earned it in the presence of Shiori, his younger sister and current (albeit reluctant) heiress to their family-run inn, who has been pressuring him to return home and resume the position neither of them truly wanted.
• Trauma Button: Iori states he's no longer a fan of maids due to being forced to dress as one in the Oumi Festival.
• Vitriolic Best Buds: Iori and Kohei fight about everything, yet despite their vastly different lifestyles, their personalities are seen as similar and spend most of their time together, partly due to having been inducted into the club at around the same time, and partly out of their chagrin over their upperclassmen's shenanigans.
• What Does She See in Him?: Chisa is a bit baffled when she notices that Naomi is in love with Iori. When Naomi learns that Chisa is apparently in a relationship with Iori, he excitedly asks what she likes about him and Chisa struggles to come up with an answer.
• What You Are in the Dark: During a trip, when Azusa and Iori are alone, Azusa offers to sleep with him. Iori, being aware that Azusa is probably subjecting him to a Secret Test of Character, refuses. That is to say, he clearly wouldn't mind doing it with Azusa, as he finds her very attractive.

Chisa Kotegawa

Voiced by: Chika Anzai
Portrayed by: Yūki Yoda

Toshio's youngest daughter, Iori's cousin and fellow mechanical engineering freshman at Izu University. Unlike her clubmates, she typically shies away from their "extracurricular activities", instead focusing on her studies and diving. Usually serious and no-nonsense, Chisa is shown to have little patience for the happenings at the club, and in particular, Iori's shenanigans.

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• Academic Athlete: Not only is she a competent diver, she is also a fairly intelligent student, as shown when she scores an impressive 80s on a German test Iori, Kohei and their friends flunked even with cheating. She is by far the most academically proficient among the underclassmen, though it shows that she lacks the life experience of their seniors.
• A-Cup Angst: Downplayed—while she actually has decent breasts (unlike Aina), she sometimes becomes self-conscious whenever she is reminded that she's smaller compared to the positively bulging Nanaka and Azusa. Later in the story, while tending to an ill Aina after a night of hard partying, Chisa catches multiple glimpses at Aina's bookshelf, which is filled to the brim with breast-growth books and guides. She tries to sneak one out, but Aina catches her red-handed.
• Beware the Quiet Ones: As Iori and Kohei fully know, eliciting Chisa's wrath is not a wise thing to do, even though they do it all the freakin' time.
• Boyfriend Bluff: After winning the Miss Izu contest, he declares Iori her "boyfriend" in front of the university's student body, partly to protect herself from unwanted suitors, partly to spite Iori for making her win in a most embarrassing manner. Iori later agrees with the charade, as Chisa is very prone to getting hit on.
• Broken Pedestal: Invoked and played with. It's shown that Chisa was expecting great things when Iori moved in, as she is fond of her memories with him during the time they spent as children. She is sorely disappointed when she realizes how easily he's goaded into becoming a party animal by the seniors of the diving club. It's also shown that in spite of this, she's expectant of seeing Iori getting his shit together, and has been fortunate of being able to catch glimpses of his better side.
• Celibate Heroine: Chisa seems to have no interest in dating at all and is more interested in finding diving friends.
• Chaste Heroine: When a co-worker in Palau jokes that Kohei and Iori could die from being blue-balled, she immediately believes it.
• Chekhov's Gun:
  • In Chapter 20, during the Okinawa trip, Chisa skips the third dive and joins Iori on a boat because she hurt her ear. This is an important detail, because over thirty chapters later, this clues Iori in, that Chisa likely suffers from the same problem that her mother did, which caused her to go deaf on one ear, and is one of the reasons why her mother doesn't wish for Chisa to become a diving instructor.
  • In the exact same chapter, Iori promises Chisa to come back again in Okinawa when he wins the lottery. When Iori wins the 300,000 yen in the lottery in Chapter 61, he invites Chisa to an Okinawa trip.
• The Comically Serious: She typically responds to most of her clubmates' (especially Iori's) shenanigans with no worse than an expression of exasperation.
• Dandere: Chisa is occasionally shy, but will speak her mind when angry or goaded enough via Death Glare and/or Tranquil Fury.
• Death Glare: One of her more common expressions due to having to put up with her clubmates' alcohol-fueled shenanigans on a near-daily basis.
• Dude Magnet: Everyone agrees that Chisa is very cute, which goes so far that Iori gets numerous death threats after she won a beauty contest and in her acceptance speech declared Iori to be her boyfriend. Chisa is especially sought after because the majority of the students in her courses are male.
• Dull Eyes of Unhappiness: Played for Laughs near the end of Chapter 35, after Naomi confesses to her that he likes Iori.
• Entertainingly Wrong: She has always been under the impression that her mother doesn't think too highly of her goal of becoming a diving instructor, mistaking her worries for callousness. It turns out that her mom is worried that Chisa might lose her hearing on her left ear from barotrauma like she did.
• Even the Girls Want Her: In that case it's even more extreme, because the woman that wants Chisa is her own sister, Nanaka.
• Green-Eyed Epiphany: In Chapter 77, after witnessing Aina and Sakurako bickering over who gets to spend time with Iori once Chisa "breaks up" with him, Chisa realizes that she's not quite okay with this or with making it any easier for them at the very least, so she declares that she doesn't feel like breaking up with Iori yet, throwing a wrench on their plans by starting to admit her intentions on the subject.
• Hidden Depths:
  • It's shown that deep inside, she wants to have a friendlier relationship with Iori, but he's not making it easier for either her, or for himself.
  • Chisa, under normal circumstances, is markedly kind, sweet and fun-loving, and has the virtue of a childlike curiosity for both her hobbies and sharing them with her friends.
  • Chisa is more susceptible to affection than she cares to show, as Iori has surprised her numerous times with how much he takes her into consideration for his decisions, and how much he wants to be in her life.
• I Don't Want to Ruin Our Friendship: After thinking that Iori gained feelings for her, she's very uncomfortable around him because she notices that he's always with her now. It doesn't help that one of Iori's main priorities during his college life is precisely to spend time with Chisa. Feelings or not, he's there for good.
• I Just Want to Be You: Chisa reveals she's jealous of Nanako's social skills and has wished countless times that she could be her older sister.
• I Just Want to Have Friends: She has always wanted to have diving friends of her age, which is why she was so expectant to live with Iori... that is, before Toki and Kotobuki dragged him from his feet, stripped him naked and wet his whistle almost nightly. While she's not that appreciative of the nightly partying of the club, she's deeply grateful of having Iori, Kohei and Aina for being there as friends she can dive with.
• I'm Standing Right Here: As she witnesses Aina and Sakurako formulating plans regarding Iori with full knowledge that her relationship with Iori is fake, Chisa starts feeling that her role as a fake girlfriend shouldn't mean that she would be just leaped over as if she were just an obstacle, so she decides to set it on stone and refuses to break up with Iori.
• Just Friends: This forms a great part of her relationship with Iori, as he is The Beard for her, and that sort of relationship doesn't work if the two parties are not friends to begin with. Though she is greatly dismissive of Iori every time he wants to involve her in something fishy, it's shown that Chisa does care a great deal about him, and is, for lack of a better term, one of the best friends she's ever had.
• Kissing Cousins: Invoked and subverted. She is Iori's girlfriend only at college, in a mutual effort by both Iori and Chisa to prevent her from being hit on. Neither have shown the actual interest to pursue a relationship of that nature, as they consider each other as their immediate family and by no means significant others, regardless of the fact that they're not blood-related.
• Like Brother and Sister: Chisa and Iori are so much in the same tune that it's close to being clockwork. They're so natural and comfortable when alone together that it's almost second-nature to them. It's not readily apparent to them, but it's as if they've spent their lives together. As a matter of fact, this is one of the reasons Aina thinks Chisa is a serious prospect for Iori, even when neither fully realize it.
• Like Mother, Unlike Daughter: Zigzagged. On one hand, Chisa inherited her quiet demeanor from her mother, and takes an awful lot after her; on the other hand, they rarely see eye-to-eye because her mother disapproves of her dream of becoming a diving instructor; then it is revealed her mother is merely worried she is also going deaf on her left ear, much like herself.
• Locked Out of the Loop: While the rest of Peek-a-Boo knows about Nanaka's abnormal love for her, no one is willing to tell Chisa about it for fear of how Nanaka will retaliate.
• Morton's Fork: Played for Laughs when Chisa asks Iori about a question on breasts; he deduces no matter what answer he gives, it's going to be the wrong one regardless. What she really wanted to know is if he really is heterosexual, because she just learned that Naomi likes Iori.
• Nice Girl: Played with. She's one whenever her friends approach her as civilized people... that means, almost never. On those rare occasions, she's shown to be a kind, gentle and doting girl.
• No Social Skills: As the series goes on, it becomes clear that she has little in the way of socialization, often focusing on diving. It is through interacting with fellow freshmen Iori, Kohei and Aina that she starts opening up. This is part of the reason why her mother doesn't support her desire to become a diving instructor.
• The Not-Love Interest: Played with. Aina considers her as serious competition for Iori's affections, even though he has stated that he doesn't have those intentions towards either Chisa or Nanaka. However, it has never been shown what Chisa's expectations of Iori are, as she seldom thinks about that sort of thing.
• Not So Above It All:
  • Most of the time Chisa is an introvert with a frugal approach to drinking alcohol. When she does get hammered, though, she can get quite a bit dorky, and during their first night at Palau she has taken to drinking together with Iori and Kohei, and is found sleeping on top of a dog and next to the half-naked boys by Aina the following morning.
  • Chisa has an extreme obsession with the ocean and diving, apparently having little to no interest in anything else that she listens to sounds from running bodies of water instead of music.
• Oblivious to Love:
  • Chisa has no idea of Nanaka's unsisterly love for her. Worse yet Chapter 49 implies that because of this, she is totally used to being glanced at lustfully thus doesn't see it as bad.
  • Until fairly recently, it's shown that Chisa has been largely unaware that Aina likes Iori. As such, her mother has to point out that Aina has been grooming up in an attempt to win him over, which didn't quite sit well with her.
• Only Sane Woman:
  • In a cast full of alcoholic, nudist weirdos, she stands out for her reluctance to get roped into their shenanigans and trying to bring order out of the chaos they create, so much so even her quirky obsession with diving would look normal.
  • This also applies to her classmates at college, which are a bunch of hormone-addled jerkasses.
• The Quiet One: Chisa is PaB's resident wallflower. It's shown that Chisa is not one to speak much or draw attention to herself.
• Reluctant Fanservice Girl: Chisa has her skirt flipped by Iori during the Miss Izu Beauty Contest (in order for her to win the contest and thus earn the club money), has been forced by Nanaka to wear a dress and skirt for the club's tennis match against Tinker Bell, was forced to join Azusa and an equally-reluctant Aina in a part-time job handing out flyers dressed in skimpy outfits to earn back the money she and her clubmates spent on shopping diving gear, was caught by Iori being groped by Nanaka and Azusa, and was again caught topless by Iori while undressing after she got drenched after falling onto the beach in a drunken stupor.
• School Idol:
  • After winning the Beauty Contest (albeit after some skirt-flipping antics by Iori), Chisa has become the toast of Izu University, specifically the mechanical engineering program (if only due to the sheer dearth of girls taking up the program, the male-to-female ratio being 140:3).
  • One of the graces of the beauty pageant ordeal comes from the fact that her clubmates consider her so pretty that they know for a fact that she'll win it by just participating. This praise alone makes Chisa willing to participate.
• Shared Family Quirks: When the freshmen visit Palau, they note that Chisa has taken a lot from her mother, from her dark hair to her introverted personality, as well as a tendency to be a bit of a dork in private, but also having hearing problems on their left ear. A more Played for Laughs example is a flustered Chisa will ask Azusa for advice just like her sister Nanaka.
• Shrinking Violet: While not as crippling as Aina's case, it's still obvious that Chisa is introverted and socially awkward, as shown when she gets flustered over being complimented "nice buddy" by her clubmates during her tennis doubles match with Aina, which she understandably mishears as "nice body" given that she was wearing a skimpy shirt-and-skirt combo (specifically prepared by Nanaka for her), and shies away from Iori and Kohei partying with their college friends in the former's room.
• Sibling Yin-Yang: Chisa contrasts her sister, Nanaka. While Chisa resembles her mother more, Nanaka is similar to her father. Nanaka is a very social person who often smiles, while Chisa tends to frown a lot and lacks social skills, and unlike Nanaka Can't Hold Her Liquor.
• Sugar-and-Ice Personality: Despite her serious attitude and a tendency to occasionally react negatively to the shenanigans around her, Iori compliments her that she is far kinder than she appears, such as foregoing the chance to join Kohei and Aina in deeper waters during the Okinawa trip to join Iori back on the boat, thinking he may be sulking over being left behind after failing to take the practical exam (and thus earn a diver's license that allows him to go to open waters) due to going down with a fever yesterday; he was actually merely seasick, but he nevertheless appreciates her concern.
• Tears of Joy: In Chapter 57, she tearfully thanks Iori for letting her know why her mother is so against her diving instructor goals (which is a more health-related matter than she thinks) and tells him that she's glad to have him close to her.
• The Three Faces of Eve: The Child to Aina's Wife and Azusa's Seductress, being the shortest of the three Peek-a-Boo girls and the most socially-awkward, with a childlike fascination for the sea.
• Too Qualified to Apply: Played for laughs. To Aina and Sakurako, Chisa is the rival to defeat in their pursuit of Iori due to various factors including cohabitation, attractiveness and their chemistry together, all despite the fact that Chisa is hilariously unaware of her own advantages over said rivals, and even not knowing that she's a contender to begin with. It's so egregious that Chisa and Iori organically behave as an experienced and stable couple whenever they're alone together, so much that it doesn't elicit questioning from either of them.
• Tranquil Fury: Aside from the use of Death Glare, Chisa has problems expressing her anger and retaliates using this trope instead, be it the girls from the Tinker Bell tennis club in a tennis match or Iori Saying Too Much.
• Unknown Rival: To Aina, in terms of their romantic prospects with Iori. Chisa doesn't realize this because she's not "tuned" for romance, but she's so close to Iori that Aina can't help but worry that she'd swipe Iori off his feet if she had even the slightest idea.
• When She Smiles: It's a rarity for her to crack a smile, given her serious attitude and having to put up with all the alcohol-fueled shenanigans around her on a daily basis, but when she does, she's downright adorable (such as when Iori expresses his gratitude for her showing him the wonders of scuba diving).
• You Keep Telling Yourself That: In spite of her low tolerance of how Iori behaves, it's shown that Chisa cares a great deal about him, and firmly expects better things of him rather than what little he has shown her since they've been living together. It's apparent how much she wants to respect him, but she can't. However, Chisa does see from time to time the better side of Iori, just like she wants him to be.

Kohei Imamura

Voiced by: Ryōhei Kimura (main) / Shouta Aoi, Inori Minase and Rie Kugimiya ("mix voices", Episode 8)
Portrayed by: Atsuhiro Inukai

A hardcore otaku and a fellow mechanical engineering freshman at Izu University alongside Iori and Chisa, the former with whom he has struck a relationship constantly zigzagging between friendship and enmity. Airheaded and equally procrastinating as Iori, Kohei lives in his own little world with his waifus.

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• Berserk Button: Being the otaku that he is, he hates it if someone in real-life is experiencing typical anime and manga clichés, such as a childhood friend calling someone "onii-chan", and will turn violent from jealousy.
• Birds of a Feather: It's repeatedly shown that Kohei is very similar to Iori in terms of personality being just as jealous, spiteful and willing to cheat as Iori at his worst.
• Celibate Hero: Zig-Zagged. Kohei states he's only interested in 2-D and has turned away real girls who are interested in him for that reason. That said, he actually finds Nanaka and Azusa attractive, proven by his nosebleeds when they appear half-naked, he may like Kaya Mizuki that way and he once hit on Kanako Iida, after seeing a Commonality Connection, not to mention his attraction to women who would call him "big brother".
• Comedic Lolicon: It's mixed with Pædo Hunt. Kohei has admitted to being interested in 2-D kids, but while he's mostly harmless, the rest of the cast react with fear and horror when his interests appear to be about real children. This is also the reason he later becomes attracted to fifteen-year-old Shiori, much to Iori's alarm (despite their mutual animosity), while he states that Chisa looks too much of a teenager to fit his perfect "little sister" mold.
• Commonality Connection: He gets along instantly with a duo of German otaku in Chapter 49 due to being otaku and fans of the Show Within a Show Blue Springs.
• Covert Pervert: Overlapping with Not So Stoic. While Kohei tries to act like he's not interested in "3-D women", he will jump at the chance to see Azusa or Nanaka naked, to say nothing of his infatuation with Kaya and later obsession with Shiori.
• Crazy Jealous Guy: When Kohei thinks someone is interested in Shiori, his first thought is murder.
• Forgotten First Meeting: Because he is too excited for the upcoming Kaya Mizuki concert at the time, Kohei doesn't remember haging out with Sakurako. When they meet again, he treats her as a stranger and covers in fear. He also doesn't remember meeting Yuichi Ikegoshi twice.
• Identical Stranger: Kohei looks exactly Yuichi Ikegoshi, a member of a boy band, minus having a lighter hair color. Ikegoshi later dyes his hair blond so Kohei completely resembles him.
• Harem Seeker: Kohei originally wanted to join a club filled with beautiful high school aged women, hoping to be the only man to gain a harem.
• Heroic BSoD: For much of the early stages of the freshmen's second Okinawa trip, Kohei is in a slump after learning that Kaya Mizuki is getting married.
• Hidden Depths: Chapter 64 reveals that Kohei has some good make-up skills, such as when he managed to transform Aina◊.
• Irony: The funny thing about Kouhei is that he's handsome enough to have a harem, but his own weird expectations and standards, and lack of self-awareness keep him from even recognizing the multiple hints that would lead him to having one.
• Little Sister Heroine: A major fan of this character archetype, Kohei gets very jealous over the idea that Shiori might have feelings for her older brother Iori or vice versa.
• Nice Job Breaking It, Hero: His and Iori's plan to force Chisa to set them up a mixer for their engineering friends through a rigged King's Game backfires when, holding the "King" stick in the last round, instead of picking whoever has the "1" or "3" sticks to set up a mixer (both numbers which Iori predicts may belong to Chisa) he misreads Iori's sign language and declares "4". Not only does this derail their plan, but it puts them at the mercy of Tokita... who wastes no time introducing Iori and Kohei's friends to his fellow beefcakes from the local rugby club.
• No Social Skills: Kohei has very little in the way of people skills switching from an awkward mess that talks as little as possible with people he doesn't know or not being able to shut up about the things he loves.
• Otaku: Kohei openly shows his love for anime and manga, considering his default attire is a shirt with his favorite character "Rarako-tan". However, he seemed to believe no one could really perceive him as one until he explained himself; partially true whenever a woman doesn't recognize the apparel he wears.
• Power Of Hate: After hearing a rumor that Ikegoshi is going to marry a seyiuu, he's so focused on murder that he doesn't feel any pain.
• Pretty Boy: Most of his female schoolmates admire his good looks (only to be rebuffed by his hobbies), which in turn makes him the envy of his male schoolmates.
• Proud to Be a Geek: Is absolutely shameless about his Otaku interests and worship of his favorite Idol Singer Kaya Mizuki.
• This Is Reality: Chapter 62 has Aina and her friends openly state dating is nothing like erogames to Kohei's despair.
• The Resenter: While Kohei doesn't care to get a girlfriend, he hates the idea of others having girlfriends.
• Shipper on Deck: By Chapter 51 even he can see that Aina is head-over-heels for Iori and does his best to help her out ... by ruining Iori's chances with any other girl. It's implied that he's not doing it to spite Iori (as Iori percieves), but rather, for Aina's sake.
• Spell My Name With An S: Due to the way Japanese long vowels can be romanized, his given name can be spelled Kohei, Kōhei or Kouhei. Kodansha Comics goes with the former.
• Squee: Kohei's reaction when not only does a diving store that the group goes to has diving suits based on Asuka and Rei's plugsuits but Iori has Chisa and Aina try them on.
• Voice Changeling: Kohei is capable of altering his voice, shown during the engineering gang's Coitus Interruptus antics against Yuu and Rie in Episode 8, pretending to be three different girls Yuu was simultaneously dating besides Rie.

Aina Yoshiwara

Voiced by: Kana Asumi
Portrayed by: Ren Ishikawa

A freshman at Oumi Women's University, Aina, or "Cakey" as Iori and Kohei call her, is part of the Tinker Bell tennis club, but leaves to join Peek-A-Boo. Enthusiastic and fun-loving, Aina is often the individual that points out the insanity of what happens at Peek-a-Boo.

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• Accent Slip-Up: When extremely nervous, Aina can sometimes slip into her natural accent.
• A-Cup Angst: Aina has the flattest chest among the Peek-a-Boo girls, and often feels inadequate compared to Nanaka and Azusa. After coming back from her hometown during the summer however, they have suspiciously, and surreptitiously, increased in size.
• Aborted Declaration of Love: Aina lets her budding affections out in her native dialect to Iori during their date, but immediately takes it back, pretending she was talking about olives, when she says "I love you".
• Beautiful All Along: Aina is a natural cutie; she just needs to lay off the excessive makeup she puts on whenever she goes out in public.
• Because You Were Nice to Me: She joins Peek-a-Boo as an expression of gratitude to Iori and Kohei for defending her honor and standing up to her former clubmates at Tinker Bell for humiliating her.
• Beneath the Mask: Whenever Aina has make-up on, she's bold and fearless, but without it, she's a dorky Shrinking Violet.
• Can't Hold Her Liquor: Only in terms of the series, but when she drink like the rest, she's one mean drunk; Justified when the club drinks strong alcoholic content (even diluted was "only" 30% when typically it's higher than 90%), but her drunken behavior often borders psychotic with regards to Iori's obliviousness to her affections for him. And without Iori around? She's just like the seniors.
• Clingy Jealous Girl: She usually dislikes Iori hanging out with women, usually with Chisa and Busujima.
• Corrupt the Cutie: Played for Laughs with her experience as a Peek-a-Boo member, having learned, in only a space of a few days, to participate in the boys' drunken binges and stripping down to her underwear.
• Cosmetic Catastrophe: She has a really bad taste in makeup, often applying excessive amounts of foundation, blush, lipstick, eye shadow, and eyelashes.
  • Averted when Kohei does her make-up and managed to transform her as seen in Chapter 64◊. Aina is even surprised and admits defeat.
• Covert Pervert: While Aina usually tells off Iori and Kohei for stripping on inertia, she actually does like looking at their bodies.
• Embarrassing Nickname: "Cakey", a derogatory reference to her heavy, horrid appearance upon using so much make-up.
• Everyone Can See It: Played with. Aina's crush on Iori is so transparent every Senpai in Peek-A-Boo knows how big it is, yet her same-age friends are not the introspective kind, so they are none the wiser. When she back-tracks her accidental Love Confession to him during their date, her slip-up is within earshot and totally obvious to the patrons at the restaurant.
• Fanservice Pack: Aina started out with the smallest bust size among the women in the club but after returning to the club following hard labor at her hometown, her breasts have increased in size tremendously. Neither Iori or Kohei want to ask what she did to increase them and even Chisa wanted to know; She's padding them, and badly at it.
• Heroic Self-Deprecation: Aina has issues with her body image, especially due to the fact that she has to share the limelight with Chisa, Asuza and Nanaka, who are gorgeous and way more buxom than her. This makes her think that they're competition for her in her pursuit of Iori, and as she percieves herself, she thinks that she's on the losing side compared to them.
• Hidden Agenda Villain: Played for laughs and subverted. During the mixer she sets up for Iori and his college friends, she does everything she can to sabotage any possibility Iori has to form a relationship with any of her friends both by caking them up with makeup and by intentionally telling them beforehand that Iori has a girlfriend. Playing it by ear and relying on Iori's friends' own thirst for girls, Aina successfully puts a lid on the mixer. As such, Iori considers Aina the villain in his book, not knowing that she did it because she's precisely aiming for him, so her intentions are more pure than he realizes.
• I Just Want to Be Loved: A shy, unassumingly cute girl, herself, versus a trio of bombshells, Asuza, Nanaka and Chisa, aiming to focus Iori's attentions on herself instead of them. Ironically, Aina has the best chance out of the four just due to the fact that she's actually trying. It's shown to be an uphill battle for her, but she's putting her all on it.
• I Just Want to Have Friends: After being forced to enter the "joke category" at the Miss Izu Pageant (alongside Chisa), a drunken Aina admits she just wanted to fit in with her college peers, even if it meant making a fool of herself.
• In-Universe Nickname: Iori and Kohei keep on calling her cakey to her annoyance.
• Nice Girl: Among the club members, Aina is the most openly pure-hearted and good-natured.
• Only Sane Man: Upon joining Peek-a-Boo, Aina becomes this for the club, but it doesn't last long if she starts drinking herself.
• Put on a Bus: She returns home for the summer to help her family out in their farm; Played for Laughs when Azusa makes it sound like she isn't coming back at all. Aina returns to the story in Chapter 50.
• She Cleans Up Nicely: Inverted—Aina's make-up skills kill any natural beauty due to how garishly cakey and heavy it is.
• Shrinking Violet: Without her makeup Aina is terminally shy and unable to interact with almost anyone outside Peek-a-Boo.
• Small Town Boredom: Aina is from a farm family and she seems pretty embarrassed by it.
• So Proud of You: She's deeply touched when she learns of the great lengths that Iori and Kohei were willing to go through to prevent her from being forced to leave due to her family refusing to pay for her tuition, only to learn that it was only for the summer break.
• Tears of Blood: Aina cries these when offering Shori her swimsuit in fear that her clothes will be the same as a middle-schooler's.
• Thinks Like a Romance Novel: In Chapter 62 when Aina describes when couples would have their first time together, she describes a very romantic moment that her friends state goes too far.
• The Three Faces of Eve: The Wife to Chisa's Child and Azusa's Seductress, being the most openly kind-hearted of the three Peek-a-Boo girls as well as the one with the most obvious crush on Iori.
• Trash of the Titans: As Iori, Chisa and Kohei discover on their first night at Palau, Aina isn't exactly a great dishwasher, seen with the pile of unwashed kitchenware on the sink of their lodging.
• Unknown Rival: Played with. Aina is under the impression that she has to compete with Chisa, Azusa and Nanaka for Iori's affections; Iori himself is not shy in expressing an admiration for their beauty, but he considers Chisa and Nanaka his closest family, while he doesn't pursue Azusa out of respect for the club's order, meaning that Aina has a better opportunity with Iori than she thinks.
• What Does She See in Him?: People outside the club often question her feelings for Iori, especially after she offhandedly mentions one of his quirks.
• What the Hell, Hero?: During one of their first dives together, Iori chides her for lying about how much air she had left in her tank. The senpai do not chide her, however, but tell her that she should keep in mind that she should rely on them because they're there for her.

The Upperclassmen

Ryuujirou Kotobuki

Voiced by: Katsuyuki Konishi

One of the headlining third-year members in Peek-A-Boo and studying for his mechanical engineering undergraduate.

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• The Bartender: He works part-time in a bar. His willingness to listen to his patrons especially attracts the women who visit him.
• Big Brother Mentor: A surrogate version to his underclassman Iori in the earlier stages of the series, not only teaching him the basic of scuba diving, but also giving him words of wisdom.
• Chivalrous Pervert: He is an excellent listener and he's very popular with the ladies at his bartending job for his willingness to lend a shoulder to cry on. That is, notwithstanding that he's a binge-drinking nudist.
• Cloud Cuckoo Lander: Alongside Toki, they have extremely off-the-wall logic regarding what's decent, what's acceptable and what's healthy.
• Early Installment Character-Design Difference: Kotobuki was much slimmer, but still muscular, in the first chapter; subsequent reappearances render him just as bodily wide as Tokita.
• He Cleans Up Nicely: While working as a part-time bartender at a local bar popular with college students, Kotobuki dresses up for the part, complete with mannerisms and an air of grace completely unlike what he's usually like in Peek-A-Boo.

Shinji Tokita

Voiced by: Hiroki Yasumoto

Another third-year member of Peek-A-Boo also in the mechanical engineering program.

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• Be Yourself: When preparing interview questions for an alumni event at a bar in Chapter 58, Tokita is given this advice by Iori and company after he does some practice. Tokita took the advice to heart too well to the point that he drank like crazy and stripped naked at the interview. It surprisingly worked out well with Tokita even getting the interviewer's business card.
• The Big Guy: Of the male club members he is the most musclebound (even more so than fellow senior Kotobuki), so much so he can easily take up home-moving jobs on consecutive days (in contrast to Iori and Kohei, who could barely carry furniture together).
• Hidden Depths:
  • He's the only person in Peek-A-Boo to be in a relationship.
  • He apparently can play the piano.
• Hypocrite: Iori and Kohei are pretty annoyed that he says he finds forcing coworkers to drink as unacceptable when he not only forced Iori and Kohei into Peek-A-Boo but also forced them to keep up with the club's insane drinking culture.
• Metaphorically True: When describing his experiences in Chapter 58 in a practice interview, his answers are technically true to Iori and Kohei's annoyance as they remember his actions.
• The One That Got Away: It's shown that Azusa has a thing for him, but she does not act on it because of Toki's girlfriend.
• What Does She See in Him?: At the very least Iori and Kohei were shocked that he has a girlfriend to the point of wondering if she was even human.

Azusa Hamaoka

Voiced by: Toa Yukinari
Portrayed by: Yūka Ogura

A third-year student from Oumi Women's University.

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• Adaptational Ugliness: Downplayed, but a common lament of manga readers is that the anime shortened and simplified her "sex hair" quite a bit, to make it easier to animate.
• Bedmate Reveal: How she makes her debut in the series—she casually lies next to Iori to sleep there during the night, without waking him up; he finds her next to him in the morning not knowing who she is.
• Buxom Beauty Standard: Azusa has the largest breasts among the three Peek-a-Boo girls, and Chisa—herself no slouch in terms of bust size—cannot help but feel insecure after she was barely able to fit her vest on Azusa when the latter walked into their Izu Spring Festival booth near-completely topless.
• Cloud Cuckoo Lander: Azusa loves being part of the chaos surrounding Peek-A-Boo, even undressing along with the men in their drunken escapades.
• Commonality Connection: She immediately connects with Iori and finds him adorable. Why? Because she heard from Nanaka he is also bisexual, like her.
• The Confidant: She is Nanaka's "friend" when Nanaka needs advice (specifically after Nanaka saw Iori's false porn collection which included gay porn). She also listens and gives advice to other members, like Aina's love life with Iori.
• Cool Big Sis: When she's not being a drunken mess, she would occasionally give sound advice to her underclassmen.
• Depraved Bisexual: Downplayed as Azusa is generally good-natured but she is explicit about her desire to sexually violate Nanaka to Iori; on the other hand, it's implied she also has a thing for Tokita (but couldn't get reciprocated given he already has a girlfriend), and during the Okinawa trip she also proposes to sleep with Iori.
• Didn't Think This Through: Azusa was the club's representative for the Ms. Izu pageant during the seniors' freshmen year, but despite being beautiful/sexy enough to have won it easily she got disqualified in the preliminaries because she forgot her swimsuit and appeared in the contest wearing her underwear.
• The Gadfly: She has said and done things just to mess with others for fun. For instance, Azusa explains to Iori about Aina's situation when she has to return home—she deliberately withholds the fact that Aina merely has to help her family at their farm during summer break, instead claiming she needs to leave because she's out of college expenses.
• Going Commando: Implied in Chapter 46 when the freshmen celebrate with their seniors.
• Hard-Drinking Party Girl: While everyone in Peek-a-Boo drinks alcoholic beverages, among the girls she is the most eager to join her male clubmates' binges.
• Has a Type: As she states, when it comes to boys, Toki; when it comes to girls, Nanaka.
• The Lad-ette: She has no problems playing strip games and drinking with the other Peek-a-Boo members. That said, she also shows a very feminine side privately.
• Lovable Sex Maniac: Azusa isn't shy about flirting with everyone, having sex talks or speak of her obsession with wanting to bed Nanaka, including giving Iori a chance to sleep with her once.
• Ms. Fanservice: Nanaka and her are the go-to girls when it comes to fanservice.
• Nice Girl: Ostensibly the nicest of the senior club members and the most reliable, even with her own brand of weirdness.
• One of the Boys: Among the few girls in Peek-a-Boo, she is the most eager to join the boys' activities.
• Please Put Some Clothes On: How Chisa reacts to her walking into their Izu Spring Festival booth wearing nothing on her top but a bra.
• Really Gets Around: Subverted. With Azusa's constant teasing and casualness, she gives off that vibe, but she actually finds it really rude when Iori indirectly accuses her to be promiscuous when she offers to have sex as friends with him once. She notes that she only offered this to Iori because she likes him (it was also a test).
• Secret Test of Character: She subjects Iori to one when she proposes to him to have sex. Gauging his response, Azusa determines how far he'd go to either protect or mess up their friendship, even when she was entirely willing to go through with it either way.
• Shameless Fanservice Girl: Not only is Azusa the bustiest and curviest among the Peek-a-Boo girls, but she also has little qualms stripping down to her underwear and join the boys' drunken escapades. And that's not to mention how she was introduced, sleeping half-naked next to four completely naked men.
• Shipper on Deck: She makes Iori keep up the Boyfriend Bluff with Chisa, knowing there's small sparks between them, while giving advice to Aina before the latter goes on a date with Iori. Azusa even believes an Iori/Kohei pairing is possible.
• Spanner in the Works: Iori and Kohei's attempts at getting Chisa drunk in order to force her to enter the Miss Izu Contest backfire spectacularly when not only does Azusa unwittingly prevents them from doing so, but also ultimately catches up to what they are doing and forces them to confess.
• Supreme Chef: She has the best culinary skills among the club members, which is why she was invited by Kotobuki and Tokita to teach the freshmen how to cook okonomiyaki for the Izu Spring Festival.
• The Tease: Azusa knows how to tickle her clubmates' sexual urges, and isn't shy about flirting with everyone.
• The Three Faces of Eve: The Seductress to Chisa's Child and Aina's Wife, being the curviest and most flirtatious of the three Peek-a-Boo girls.

Grand Blue Staff Members

Nanaka Kotegawa

Voiced by: Maaya Uchida
Portrayed by: Aya Asahina

Chisa's older sister, Toshio's oldest daughter, professional diving instructor, and manager of Grand Blue.

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• Ambiguously Gay: While her sexuality is never flat-out stated, her affections towards her sister are, at least to some degree, that of a sexual nature.
• Beware the Nice Ones: Nanaka is usually the most mellow character in the main cast, but as Iori comes to discover (much to his horror), anything Chisa-related is bound to set off a dangerously psychotic side.
• Boob-Based Gag: Nanaka has the largest breasts of all the main females (surpassing Azusa), and is prone to occasional bouncing. During the Okinawa trip, Iori can barely concentrate on his diving licensure exams after having to sleep between her and Azusa the night before, and even miswrites his given name as "Boobs" while taking a written test in her presence.
• Camera Fiend: Whenever Chisa is going to be cute, expect to see Nanaka have a camera with an incredibly long zoom lens to take pictures.
• Can't Hold Her Liquor: When Aina throws an all-girls' drinking party, Nanaka looks like she's hammered throughout the event; subverted when Toshio explicitly tells Iori the day after that she has high alcohol tolerance, a bad thing for Iori because he lets slip that he's in a false relationship with Chisa, which Nanaka overheard during the party.
• Chaste Hero: Extreme love for Chisa aside, Nanaka doesn't get romantic love at all. She's generally puzzled when anyone shows any form of romantic or sexual attraction. This is pointed out by Toki and Kotobuki, and later Azusa implies that between Nanaka, Toki, Kotubuki and herself, their group dynamic functions the way it does because something did happen in the past.
• Cool Big Sis: Besides being Chisa's actual older sister, she also acts as a surrogate one for her cousin Iori.
• Entertainingly Wrong: Nanaka is left under the impression that Iori is a massive pervert and a porn addict. This is Toki, Kotobuki and Kohei's fault, and due to awful timing on her part. Though he clears up most of the misunderstandings, Nanaka is still low-key wary of him.
• Forbidden Fruit: As stated in Like Brother and Sister, Iori tells her that he won't deny her beauty, but that this attraction is not something he will act upon because he respects her and considers her family.
• Innocent Fanservice Girl: Nanaka is pretty ok with stripping due to her job as a diving instructor.
• Hidden Depths: Just like Chisa, Nanaka expects good things for Iori, but her impression of him (unlike Chisa's) is built upon being Entertainingly Wrong about their mutual interactions, where Iori comes off as more of a pervert than he actually is. However, she denies him no kindness regardless.
• Like Brother and Sister: Invoked. Iori tells Nanaka that he does find her to be stunning, but after he stumbles to make his point clear and makes things awkward as hell between them, he states that this is not what he wants from her, as he considers her his sister.
• Lipstick Lesbian: Is shown to be very feminine, and currently shows no kind of attraction towards men. She is, however, shown to be quite fond of her own sister.
• Ms. Fanservice: Nanaka is one of the bustiest members of the main female cast, and is often shown in attire and/or postures that show off her generous proportions.
• My Sister Is Off-Limits: Subverted. While Nanaka is very protective of Chisa, she wouldn't mind Iori marrying Chisa, as long as Chisa is happy, and she knows Iori is a good person. However, after learning that Chisa and Iori going out is just a Boyfriend Bluff, she orders Iori to make sure no one else is hitting on her little sister.
• Nice Girl: There's little to nothing she's not willing to help with if she's asked to, that is, as long as it doesn't involve courting Chisa.
• Noodle Incident: Toki and Kotobuki are quick to tell Iori that approaching Nanaka is a lost cause, implying that they were interested in her in the past and did try themselves to approach her to no avail. Later, Azusa tells Iori that a lot happened in the past between Toki, Kotobuki, Nanaka and herself, to explain why they are such close friends now.
• Paralyzing Fear of Sexuality: Nanaka becomes a blushing mess when the topic of sex comes up and was terrified of Iori when she overheard him say he was attracted to her. He has to clear up that this is not his wish, as he considers her his older sister which relaxes her.
• Rage Breaking Point: She hits hers when she finds Iori and Chisa on top of each other in Chisa's room in Chapter 26.
• Room Full of Crazy: Given her character archetype, Nanaka's bedroom is filled with pictures of Chisa.
• Shared Family Quirks: Other than her yandere tendencies and raging lust for Chisa, by large Nanaka has inherited her father Toshio's mellow personality.
• This Is Unforgivable!:
  • Thou shall not court Chisa.
  • There are few things that make Nanaka mad, but if there's a hint that Iori is not being faithful to his agreement with Chisa to be her Boyfriend Bluff / Beard. This is connected to the possibility of someone courting Chisa.
• Yandere: Nanaka will kill anyone who attempts to flirt with Chisa, even demanding Iori ensures no man throughout the Oumi Women's University festival will hit on her; taken further when she catches Iori and Chisa in a compromising position, citing Iori must marry her sister.

Toshio Kotegawa

Voiced by: Shinji Kawada
Portrayed by: Masahiro Takashima

Chisa and Nanaka's father and owner of Grand Blue.

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• Ambiguously Brown: He has dark skin compared to his daughters, who don't share the same skin tone. Justified because he spends more time in the sun than the rest of the cast.
• Eyes Always Shut: Toshio is never seen with his eyes open before.
• Satellite Character: Aside from being a relative of Iori, there is nothing much about Toshio as he rarely appears and doesn't join PaB in their parties or trips.
• Wham Line: When Toshio is told about the possibility of Iori's affections going out of control for his cousins, he reveals his daughters and Iori are not related by blood.
  Toshio: That's crazy, even if they aren't blood-related.

Izu University

Hajime Nojima, Shinichirou Yamamoto, Yuu Mitarai and Kenta Fujiwara

Voiced by: Takuya Eguchi (Hajime), Jun'ya Enoki (Shinichirou), Natsuki Hanae (Yuu) and Robert Waterman (Kenta)

Left to right: Hajime, Yuu, Shinichirou and Kenta

A group of first-year students in the mechanical engineering program, they strike up a friendship with Iori and Kohei.

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• Adapted Out: Mitarai and Fujiwara are absent in the live-action movie.
• All Men Are Perverts: Almost all their scenes have them fantasizing of getting a girlfriend.
• Brain Bleach: In Chapter 44, Yamamoto is in love with a virtual idol that unbeknownst to him, is actually Kohei. 20 chapters later, Kohei finally reveals this to Yamamoto, much to his disguist as well as causing him to bleed from his eyes and cough out blood.
• Book Dumb: Like Iori and Kohei, all four of them are not book smart.
• Childhood Friend Romance: Mitarai is in such a relationship with Rie Ohashi, who addresses him as "Onii-Chan" during their childhood.
• Entertainingly Wrong: During the mixer in Chapter 59, Iori pulls out a lie detector and asks if the participants are interested in anyone present. Azusa and Nanaka affirm that this is the case, and since Fujiwara, Yamamoto and Nojima think that Kohei is only interested in 2D-characters and that Iori is in a relationship with Chisa, they conclude the girls are interested in one of them. What they don't know is that Azusa was thinking about Nanaka, while Nanaka was thinking about Chisa.
• Eyes Always Shut: Mitarai almost never opens his eyes.
• The Generic Guy: It's a Running Gag that Fujiwara is so physically bland and the most taciturn out of the group, no one pays any attention to him. This is particularly prominent during their visit to the Oumi Festival's maid cafe, when none of the waitresses take his order.
• Mundane Solution: When Chisa is given a group ticket for four at the Oumi Festival, the men, including Iori and Kohei, fail to impress on her why they should be invited. However, Fujiwara offers the best suggestion—if invited, he will not cause any trouble for her. The men are surprised because Fujiwara's solution of "what he wouldn't do to her" compared to their "what they would do for her" almost entices Chisa enough to say yes. Subverted when Rie gives Mitarai a group ticket after some pleading, making their efforts moot.
• Small Name, Big Ego: These guys know that they are complete losers but will tell rather long story of beign popular in their school years having a girlfriend in the past just so they could be popular.
• Virginity Makes You Stupid: Zigzagged; with a goal of losing their virginity on their minds constantly, the four can be often seen as Book Dumb, yet if push comes to shove, such as a sudden pop quiz by the Sadist Teacher, they'll turn competent and logical, scoring in the acceptable low 70s.
• Vitriolic Best Buds: They, Iori and Kohei have such a bad habit of pissing off and/or trolling each other, any outsider would be forgiven for wondering why they are even friends in the first place; that said, if any outsider decides to be a dick to them, they will stand up in each other's defense, such as Iori criticizing Sakurako's own criticism of Kohei's otaku hobbies, or standing up to Ushironomiya's sadistic teaching regimen.
• With Friends Like These...: Given the amount of fighting, sabotage and abuse these guys do to each other in the name of preserving camaderie makes one wonder how they even manage to strike a friendship in the first place.

Captain Kudou

Voiced by: Jun Fukuyama

Captain of the Tinker Bell intercollegiate tennis club.

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• Butt-Monkey: His tendencies to be a jackass is offset by the frequency of his misfortunes, such as being humiliated in front of his own fangirls at the Izu Boys' Pageant after mistakenly confessing to Iori (disguised as Azusa), feeling the wrath of Kotobuki and Tokita's brute-force tennis tactics, and getting stuck on the bottom of a cliff with Iori who also fell while escaping Chisa, whom he caught topless earlier.
• Handsome Lech: Kudou is one of the better-looking males in the cast, and in his first appearance alone he tries to hit on Azusa and Chisa, much to their chagrin.
• Hoist by His Own Petard: His Handsome Lech tendencies come back to bite him in the ass when, during the Izu Boys' Pageant, he apparently out-charms Kohei in proposing to Azusa... only for the "Azusa" among the audience to reveal "herself" as Iori in drag all along.
• Humiliation Conga: In retaliation for his humiliation of Aina, and to prove a point to her that nobody will forever laugh at someone or be forever a laughingstock, Iori, Kohei and Azusa set him up for a self-inflicted publicity disaster (see above).
• Ironic Echo: According to Aina, he told her to go home now that he and their male clubmates were done laughing at her horrid appearance. Those words get thrown back at him by Iori and Kohei after making a complete fool of himself by confessing to the former disguised as Azusa.
• Jerkass: He's a complete asshole to anyone he wants to toy with, such as exploiting poor Aina's need for friends by making her enter the Miss Izu Pageant with heavy makeup.
• Manipulative Bastard: During the Beach Episode, he tries to get Iori and Kohei to let them hang out together with Peek-a-Boo in order to score with Chisa, Azusa and Nanaka. Seeing that the latter two aren't in any mood to negotiate, he challenges them to a series of tennis games. They agree, on the condition they don't hang out if they lose.
• Smug Snake: Kudou is confident in his charisma and talents, which naturally makes him prone to a lot of rude awakenings once it turns out other people can outmatch him.
• Took a Level in Kindness: By his third appearance, Kudou, while still having his own agenda, is a much more civil person. Despite his rivalry with Iori and Kohei, he is actually on good terms with Kotobuki and Toki. He also gives some advice to Iori on preparing a farewell party for the seniors.

Ushironomiya

An assistant professor in the mechanical engineering program.

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• Bad Boss: Chapter 40 shows he's just a horrible of a boss as he is a teacher. The students working in his lab only sleep 10 hours a week. The only upside are the students that graduate from his lab are well regarded due to surviving this hell.
• Insistent Terminology: Despite still being an assistant professor and awaiting Izu University's approval, he insists he's a "full professor".
• Large Ham: The man cannot say a single sentence without making an exaggerated pose.
• Laser-Guided Karma:
  • He gets his just desserts when Iori and company trick him into crushing his genitals after he forced them to do the same.
  • In Chapter 55.5, he refuses to cancel his lecture despite breaking the air conditioner making the room broiling to maintain his record. Iori and co are able to bribe him with ice cold beer provided they can also get a drink. He accepts just in time for the president of the university to see him drinking thus not recommending him for a promotion.
• Sadist Teacher:
  • He forced his students to crush their genitals via the Charpy Impact Test as revenge.
  • He refuses to cancel his lecture despite personally breaking the air conditioner to retain his record. He then ensures that the entire class has to suffer with him or they fail because he refuses to suffer alone.
• Sitcom Arch-Nemesis: The guys in Iori's class have an ongoing feud with Ushironomiya which is the focus of every chapter he appears in.

Yukiko Hayashi

One of only three women in the Mechanical Engineering program.

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Oumi Women's University

Kanako Iida, Kiyoko Kamio and Keiko Suzuki

Voiced by: Yuuko Gibu (Kanako), Yuka Iguchi (Kiyoko) and Ai Kayano (Keiko)

Top to bottom: Kiyoko, Kanako, Keiko

Aina's freshmen friends.

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• Alphabetical Theme Naming: Each of their given names start consonant-wise with a "k", and also end syllable-wise with "-ko".
• Beautiful All Along: Much like Aina, the three girls are far better-looking without all that "cakey" makeup.
• Berserk Button: They get pissed off when Aina reveals she has trouble putting on weight; Played for Laughs considering the three have far more shapely figures compared to Aina.
• The Corrupter: Played for Laughs—Keiko admits whenever someone is innocent and pure, she feels the need to corrupt them. Lampshaded upon telling Kanako about a Pun on anal sex.
• The Gadfly: The three love giving Aina a hard time about what to do with her feelings for Iori when she asks him out on a movie date. Kanako is also often a victim of the other those since they consider her the most innocent after Aina.
• The Reveal: Kanako is actually the younger sister of Idol Singer Kaya Mizuki, née Maya Iida.
• Those Two Guys: Downplayed with Kanako but she at least appears by herself occasionally and has her own character. Kiyok and Keiko on the other hand, seldom appear apart from each other.

Rie Ohashi

Voiced by: Saki Yamakita

Yuu's Childhood Friend and freshman.

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• Childhood Friend Romance: With Yuu.
• Clingy Jealous Girl: Poor Yuu usually ends up a bloody pulp if Rie hears any hint of him flirting with other women.
• Cute Bruiser: She's one of the strongest characters in the cast, comparable to Kotobuki and Tokita.
• Irony: Yuu actually has every intention of being faithful to her and be a doting boyfriend, but out of jealousy his friends like to throw him under the bus whenever he wants to be with her.
• Muscles Are Meaningless: She's as strong as Kotobuki and Tokita, who are huge walls of muscle, while Rie is very slender.
• Spell My Name With An S: Due to the way Japanese long vowels can be romanized, her family name can be spelled Oohashi, Ōhashi or Ohashi, though Kodansha Comics goes with the latter.
• Yandere: Zigzagged; on one hand, she thinks Yuu is cheating on her with other women when his friends are deliberately sabotaging him from having sex with her and Iori is Trolling him during the maid cafe event, making her physical repercussions on him more akin to that of a Tsundere, but when Yuu is caught "cheating" (he claims he merely exchanged phone numbers with a co-worker) and proposes to marry Rie in order to avoid her wrath, her Slasher Smile indicates she wants to monopolize him for herself.

Sakurako Busujima

A freshman and Iori's bane. She first shows up at the Oumi University Festival, where she attempts to hang out with Iori and his friends (especially Kohei). She works part-time at a restaurant, which is how she and Iori cross paths again, when he begins to part-time work there as well, and she volunteers to "mentor" him. Over time, she actually develops feelings for Iori.

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• Alpha Bitch: The first time she is shown, she is portrayed as extremely petty, as she steals Kohei's concert ticket when he refuses to spend time with her and her friends and instead wants to go to Kaya Mizuki's concert. She also is mercilessly abusing Iori, when he begins to work at her place and she is tasked to train him, as revenge for humiliating here earlier. After getting to know Iori better, she warms up to him and becomes more of a Lovable Alpha Bitch.
• Bad Boss: She takes advantage of being Iori's senior at their part-time job to abuse him. This is treated humorously though, and Iori takes this treatment in stride, not being phased negatively in the slightest, thus continuing the humorous cycle over and over again.
• Birds of a Feather: She actually gets along with Iori and later Kohei because they're all Green Eyed Monsters that can't stand others being in happy relationships.
• Black Comedy Rape: Invoked; Iori thinks her idea of "using her weapons" against Naomi is tricking him into a sense of vulnerability, tasering him unconscious behind his back, then dragging him to a Love Hotel to get what she wants from him.
• Clingy Jealous Girl:
  • She openly tells Iori that she would treat him even worse at work than she already did, after she learns that Naomi (the boy she's pining for) is in love with Iori.
  • She shows signs of jealousy when she learns that Iori is apparently in a relationship with Chisa, not realizing that it's just a Boyfriend Bluff. She starts talking harshly to Chisa while on their coincidentally joint-trip on an uninhabited island, and after the summer break during the mixer in Chapter 59 indirectly states her hope that Iori has broken up with Chisa, only to be visibly disturbed when Kohei mentions Iori and Chisa's trip to the Kitahara Inn and Palau. In the same chapter, she forces Iori to take the lie detector test while excluding out his choice of Azusa and Nanaka. In Chapter 62, it's implied she gives Iori a lot more shifts in their part-time job to prevent him from taking a trip with Chisa.
  • In Chapter 65, she actually follows Iori in Okinawa after hearing his vacation trip and kisses him in front of the main gang which resulted with Iori Fainting.
    • Next chapter details how she ended up finding Iori and the end of the chapter has her fighting Aina and Chisa over the "right" to "keep" Iori for the night.
• Cry into Chest: A variant, after Sakurako's Love Confession got rejected by Naomi, Iori gives her a can of beer and comforts her. She then asks Iori to turn around for her to cry unto his back, stating that she doesn't want to cry unto his chest.
• Hopeless Suitor: Unfortunately for her, Naomi is not interested in her at all, partially because of their Incompatible Orientation.
• I Just Want to Be Loved: Implied. Beneath her claims of superficial relationship goals, her dedication to pursuing Naomi made even her friends question whether her boasts are truth. As Iori realizes, they're not.
• Love at First Punch: She begins to harbor a crush on Iori for his guts to stand up to her and defend Kohei's life choices.
• Love Confession: She confesses to Naomi and gets rejected. Iori helps her get better. Later in Chapter 66, she outright tells Iori that she likes him. How Iori chooses to pursue this remains to be seen.
• Loving Bully: As much as she is attracted to Iori, she cannot help but express herself by teasing and/or trolling him, especially during his stint as her junior at a part-time job. Their bickering yet closeness (like Iori being on a First-Name Basis while they are in the presence of others) is interpreted as Belligerent Sexual Tension by Aina.
• Ship Tease: She has a subtle attraction for Iori, who doesn't recognize it partly due to his obliviousness, partly due to his disgust with her Alpha Bitch antics. Later her subtleness goes out the window when she becomes outright assertive in wanting Iori for herself, kissing him in front of her love rivals, Aina and Chisa.
• Single Woman Seeks Good Man: While apparently only being attracted to Naomi because of his good looks, it becomes apparent that she also likes him because he's a Nice Guy. For similar reasons, she seems to grow attached to Iori over time, as he tolerates all of his friends' quirks and tastes, like Sakurako apparently only liking Naomi because of his physical attractiveness.
• "Shut Up" Kiss: In Chapter 65, after finally finding Iori in Okinawa, she kisses the latter in front of the main gang which results in him Fainting. She does it to him again in Chapter 66, not that he seems to mind.
• Took a Level in Kindness: Iori's earnest attempts to support her in her relationship with Naomi (despite her being aware that Naomi likes Iori) slowly make her become a better person. While she still tries to act the Alpha Bitch in front of her friends, privately she becomes nicer.
• Tsundere: Implied to be the Harsh type for Iori. During the mixer in Chapter 59, the participants play a lie detector game, where she apparently lies (to herself as well) that there is no one present who is her type. She gets away with it, when the others comment that she was probably thinking about Kohei, who she was pining for when they first met. The implication is gone by Chapters 65 and 66; she does like Iori but hides her feelings behind her harshness. Though when she shows her sweet side, it lights up the room with how sincere she is.
• Unfortunate Name: She never gives out her surname because "busu" can also mean "ugly" and "poisonous".
• Villain Respect: She tells Iori in more than one occasion that she loves the fact that he's not shy about suggesting physical violence, blackmail, and other underhanded methods to deal with problems. Given that she's willing to do the same thing, this makes them two peas in a pod.
• Vitriolic Best Buds: While she and Iori fight like cats and dogs, they do get along well underneath it all. She later falls for Iori

Other Characters

Shiori Kitahara

Iori's little sister. Shiori is in her third-year of middle school and comes to Grand Blue to visit her brother just before summer vacation starts. After Iori went to college, she became the new heir apparent of their family's traditional inn.

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• Annoying Younger Sibling: Iori doesn't exactly appreciate her company, to say nothing of her personality, especially when she visited at a most inopportune time, just when he was preparing to continue his diving licensure exams at home. This, and a desire to escape the family business, is one of the reasons he fled for Izu.
• Aw, Look! They Really Do Love Each Other: While Iori knows almost nothing about her, he cares about her enough to know that she, like him, doesn't want to inherit the family inn. Likewise, Shiori secretly misses her brother despite resenting him for leaving her.
• Beneath the Mask: Has two. While she gives off the vibe of a naive and Hopeless with Tech Yamato Nadeshiko, who really likes her brother, she is a tech-savvy woman who doesn't like her brother because he abandoned his duty and her parents have given up on Iori in favor of Shiori. However, it's shown that even with her hidden agenda, she actually loves Iori and misses him considerably, and is markedly upset, not only at being left to inherit the inn, but also because he left her alone in the first place. Shiori doesn't want to be bound by her parents' inn either, and wishes to be free like her brother.
• Big Brother Attraction: Double Subverted. On the one hand, she despises Iori for fleeing the family inn and leaving her to fend for herself when it's supposed to be his responsibility as her older brother, no matter how much of a dunce their parents and she thinks he is; on the other hand, when she has to leave home Azusa notes that she wanted to enjoy the same kind of freedom Iori enjoys, suggesting she doesn't think so little of him.
• Bitch in Sheep's Clothing: She pretends to be a Yamato Nadeshiko when she's actually a Manipulative Bitch hoping to deter her brother from running away to college and return home to inherit the family inn because she doesn't want that duty herself.
• Celebrity Resemblance: Kohei admits to Iori that part of his infatuation for Shiori (besides being a little sister) is her resemblance to "Kirara Yoimachi", a kindergarten character from another Show Within a Show, Blue Spring.
• Clingy Jealous Girl: After spying that Iori went to a little sister cafe, that Kohei dragged him to, Shiori lies to their parents that Iori called saying he doesn't want allowance for a few months.
• Cuteness Proximity: Many people find her adorable since she resembles the anime character "Kirara Yoimachi". This unfortunately leads her to be stalked by a group of perverts of both genders.
• Death Glare: She can pull off some amazing ones.
• Hopeless with Tech: Lampshaded by Iori, who claims she doesn't know how to operate a computer to send an e-mail, given she still writes letters via pen and paper. Subverted when a stuffed animal she sends to him in the mail is a sophisticated camera/microphone receiver she built to monitor Iori's activities.
• Hyper-Awareness: She knows a pervert when she sees one, as evidenced when she realizes Carina has set her sights on her, and is rightfully horrified at Chisa's obliviousness towards Nanaka and Carina's lustful overtures, going so far as to immediately hand Iori his passport, partly so he can join the freshmen's upcoming Palau trip, partly to keep him away from Carina who has expressed an intention to marry Iori in order to get close to her.
• I Just Want to Be Free: Like Iori, she also doesn't want to run the family inn, but was forced to by their parents after Iori fled for Izu. Being forced into an unwanted position partly fuels her resentment towards Iori.
• Jerkass Realization: While she is still determined to force Iori to return home, upon seeing him in high spirits going into a diving session (where he also finally gets his professional license), as well as being invited by Nanaka to also try out scuba diving for herself, she begrudgingly admits that she has gained some insight as to why Iori chooses to stay with their uncle and cousins at Izu.
• Just a Kid: During Iori, Chisa and Kohei's trip to their family-run inn, while reviewing surveillance footage of Iori protecting her from Kohei and two male German otaku, Shiori complains that she's no longer a child her brother needed to protect.
• Kimono Is Traditional: Played with; she might be seen wearing it at nearly all times, but she hates it and only does so to maintain her Yamato Nadeshiko facade to her family.
• Please, Don't Leave Me: While she's upset at being left to inherit the family inn, it's also implied that she's more upset at the fact that her brother left her.
• Shared Family Quirks: Oh, she's Iori's sister alright! It's shown that Iori's underhanded methods to deal with his problems are shared by his sister too. She's actually quite a bit like Iori from their similar expressions when their plans fail, and their glorious death glares.
• Tsundere: Her feelings for her brother depend on the situation. She pretends to be a brocon in front of others, but behind everybody's back, she is a Manipulative Bitch who tries to get Iori to their family inn whatever it takes. Deep down however, she actually loves her brother.
• What the Hell, Hero?: She does not appreciate the fact that Iori left her behind to inherit the family business.

Kaya Mizuki

Voiced by: Nana Mizuki

An Idol Singer and voice actress of Kohei's favorite character Rarako-tan.

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• The Cameo: In-Universe, Kaya is one of the waitresses at the maid cafe during the Oumi Festival. Hilarity Ensues when Kohei realizes too late the day after Kaya's concert at the university that he was working at the cafe alongside his idol before leaving to help set up the concert.
• Casting Gag: Kaya's voice actress, Nana Mizuki, is a real-life Idol Singer. Perhaps not coincidentally, the news of her marriage occurs on Chapter 64 (during Iori, Chisa, Kohei and Aina's second Okinawa trip), published months after Nana Mizuki announced her own marriage on July 2020.
• Given Name Reveal: "Kaya Mizuki" is her stage name; she's Kanako's older sister Maya Iida.
• Idol Singer: She is popular among the otaku with Kohei being obsessed with her.

Naomi Otaya

A high school student working as a chef at Iori's part-time job.

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• The Ace: Not only does he got the looks to be a major ladykiller (in spite of his own crush on Iori), but he's also pretty accomplished for a twelfth-grader, being the club leader of his own diving club with Kotobuki even stating he's around instructor level, as well as being the head chef of a family restaurant.

• Expy: His androgynous appearance and affections for the male protagonist are a throwback to Hideyoshi Kinoshita of Baka and Test: Summon the Beasts, Kenji Inoue's prior work before Grand Blue.
• Nice Guy: Compare to Iori's first meeting with his clubmates and classmates, he is surprise what a well manner boy Naomi is.
• Straight Gay: He has an open crush on Iori.

Sayaka Kotegawa

Chisa and Nanaka's mother and the manager of Dophin diving pad at Palau, where Chisa, Iori, Kohei and Aina work part-time during summer break.

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• Ambiguously Brown: Like her husband, Sayaka has dark skin while her daughters have light skin tone.
• Anger Born of Worry: She is against Chisa becoming an instructor because she became deaf on the left ear due to diving, and Chisa happens to have the same problem.
• Because I Said So: Played with. In Chapter 55, it's revealed that Chisa's mother not only disapproved of her dream of becoming a diving instructor, but forced her to take up engineering at Izu University, creating tension between them during the freshmen's Palau trip. Then it is revealed that her mother is merely worried that Chisa is also developing barotrauma-induced hearing problems on her left ear, much like herself.
• Cool Shades: Wears one around even during late evening.
• Cruel to Be Kind: She balks at Chisa's dream of being a diving instructor with her poor social skills, though only because she fears Chisa would also become permanently deaf on her left ear much like herself.
• Disappointed in You: Sayaka is rather disappointed in Chisa for her poor social skills.
• Don't Call Me "Sir": When Iori refers her as "Auntie" during working hours, she ignores him until he calls her boss. Subverted as it turns out she isn't ignoring him but couldn't hear and only hears him after she turns her head.
• Fantasy-Forbidding Father: She dismisses her daughter's dream of becoming a diving instructor. This is due to the fact that she became permanently deaf on her left ear due to diving, and her daughter is also starting to exhibit the same signs.
• Innocently Insensitive: Turns out, she wasn't trying to be cold to Chisa; due to her deafness on her left ear, she literally could not hear a significant part of Chisa's interactions, and combined with her stoicness, left a negative view of herself on Chisa.
• Missing Mom: She is missing for most of the series until Iori and his friends visit to Palau. In fact, both her daughters haven't met her for some time.
• Only Known by Their Nickname: She is only referred as "boss" by her staff and "Auntie Kotegawa" by Iori. Her first name is unknown.
• Oral Fixation: She tends to have a lolipop in her mouth.
• Parents as People: She hasn't been much of a presence in Chisa and Nanaka's life, and in what few interactions she and Chisa had during the freshmen's Palau trip they don't exactly get along well, largely due to a combination of their similarly introverted personalities and her fear that Chisa is going deaf on her left ear like her.
• Poor Communication Kills: She's merely worried about Chisa, and, due to her own physical damages, wants her daughter to have a future outside of diving, but can't articulate herself very well. There is also the occasional problem that she literally couldn't hear her daughter, because Chisa was talking to her mother's deaf ear.
• Small Role, Big Impact: It's implied that most of Chisa's insecurities about herself come from her frayed relationship with her mother.
• The Stoic: She retains her stoicism during any situations, even when she is involved with her staff's shenanigans or lecturing her daughter.
• Strong Family Resemblance: Aside from their cold personality, Chisa also inherits her mother's eyes.

Yuichi Ikegoshi

A member of the boy band, Sips, Ikegoshi first met Iori and his friends while they are at Palau. Bearing a resemblance to Kohei, Ikegoshi chooses him to be his double after Ikegoshi is injured during a dive. Since then, Ikegoshi dyed his hair blonde, which gets people to mistaken Kohei often as him. He is engaged to Yurika Muranaka, a seiyuu.

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• Chekhov's Gun:
  • Ikegoshi managed to convince Kohei to be his double by getting an autograph from Yurika Muranaka. A few chapters later, it turns out he is engaged to her.
  • It also causes problems for him when she thought he was cheating on her after seeing Kohei fawning over Aina because of the hypnosis.
• Identical Stranger: He greatly resembles Kohei, only with darker hair. By the end of his trip at Palau, Ikegoshi dyed his hair blonde, making him identical to Kohei.
• Mistaken for Cheating: Due to his and Kouhei's Identical Stranger status, his fiance thought he was cheating on her with Aina. Hilarity Ensues.
• Tempting Fate: Despite Iori and Aina's warning that Kohei is weird, Ikegoshi still allows Kohei to be his double, believing that being weird will make things more intresting.

Carina

The sole female of a group of German Otakus whom Iori, Kohei and Chisa met during their trip to Iori's family inn. Though initially presented as the most level headed member of them, Carina is actually the biggest pervert of her group.

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• All Women Are Lustful: Likely the biggest pervert in the series, even more than Iori and his friends. All her thoughts are practically something lustful, especially when either Iori or Shiori is involved.
• Depraved Bisexual: She's obsessed with Shiori and has the idea that if she marries Iori, she gets to have sex with Shiori too.
• Everyone Has Standards: On the receiving end, Iori wants nothing to do with Carina.
• Sibling Triangle: Carina plans to marry Iori because she can have Shiori too.