[[quoteright:275:https://static.tvtropes.org/pmwiki/pub/images/rsz_51ns7kmockl.jpg]]

[[TheHero Taiyo Nakabaru]] is on a school trip to Okinawa. While he is there, he wants to go SCUBA diving off the waters of Zamimi Island, the place where his father disappeared 10 years previously. He gets off the plane at the airport and tries to help a girl with some luggage. A conversation about SCUBA Diving ensues, but when Taiyo lets slip that he wants to see the ocean that his father disappeared in 10 years ago, the girl slaps him and blames him for her mother's death. Taiyo doesn't remember anything about it. Taiyo is then introduced to the Miyara sisters: The oldest is Nagisa Miyara, a diving instructor and the owner of Blue Wave Diving rental shop. Shibuki Miyara, the girl who slapped him, is around Taiyo's age. Finally, there is Mio Miyara, a stoic girl who is younger than the rest of the cast.

However, the vacation Taiyo anticipated is quickly interrupted. He soon witnesses a strange symbol shining from the water, and immediately afterwards in shoved off a cliff, landing in the sea. In it, he sees a white humpback whale. That is not all. Because Taiyo is broke and SCUBA Diving is expensive, he winds up working for Blue Waving Diving Service. Over time, more strange incidents involving the symbol occur, the plot thickens, and more character appear. Motivations and allegiances remain uncertain, characters find themselves at cross-purposes, and the mystery of the symbol becomes ever more pressing.

The series is a mixture of Romance, SliceOfLife, Mystery, and Harem. The beginning of the story is rather slow, focusing more on Taiyo's experiences with first coming to Okinawa and the daily activities in running a dive shop.

The series can be compared to ''Manga/UmiNoMisaki'' in that they are both romance series set on fictional Okinawan islands. They both have a dreamy feel to them as well as feature character development and mystery. However, ''Umi no Misaki'' has a dreamy feeling that could be described as pleasantly relaxing. IO has a sense of supernatural, unreal urgency about it that makes it a rather gripping read once the plot gets going.

----
!!This manga provides examples of:

* AboveTheInfluence: Mio makes a number of attempts to seduce Taiyo into having sex with her, and while he steadfastly turns her down he initially wonders how long his resolve to do so can last.
%%* AbusiveParents
* AbusivePrecursors: While whether the ruins, symbols, and lights were created by people or aliens, is never explored, it still doesn't get much more abusive than forcing future generations to practice ritual murder.
* ActionSurvivor: Taiyo becomes this. He's fallen from a high cliff multiple times, survived Nitrogen poisoning, Oxygen toxicity, being attacked by a mercenary, rescuing several people from drowning, massive underwater explosions, being captured by guerillas, evaded armies, and other attempts on his life.
* AdvancedAncientAcropolis: Several. Attempting to explore one of these almost proves fatal for Taiyo and Shibuki. [[spoiler:It's eventually revealed they belonged to a prehistoric whale-worshipping culture, which Taiyo is descended from.]]
* AllWomenAreLustful: Mio repeatedly tries to seduce Taiyo, and Mar succeeds in having sex with him after drugging him with coca tea.
* AnArmAndALeg: Subverted by Henri Hans; he hasn't lost his limbs so much as become paralyzed without visible reason.
* AnimalWrongsGroup: Nirvana is seemingly an environmental activist group turned terrorist organization. [[spoiler:They're revealed to be a sector of the US military opposed to the effort to activate the ruins.]]
* AnimalNemesis: The white whale to a surprising number of people.
* AnimalMotifs: Whales show up a lot.
%%* ArcNumber: 10
* ArtEvolution: The earlier character designs feature more heavily angular lines which have the unfortunate effect of often making characters look peeved, or giving them a rape face.
* AsLongAsItSoundsForeign: Lago, a quarter-Japanese girl living in Peru. Averted for most other Europeans, who have sensible European names, including Lago's sister Mar.
* AuthorAppeal: Loads of gratuitous scenes of girls in bikinis, as well as more wet t-shirts than scientifically plausible.
* BabiesEverAfter: Taiyo and [[spoiler:Shibuki]] have a son named Kai in the epilogue.
%%* BeamSpam: Coupled with LightIsNotGood
%%* BerserkButton: Taiyo's is not being able to save people
* BigBrotherInstinct: Causes a good deal of drama late in the manga involving Mio, who has romantic feelings for Taiyo.
* BittersweetEnding: [[spoiler:The mystery is solved and the cycle is broken, but the island is mostly destroyed by a landslide caused by a nuke left at the bottom of the ocean.]]
%%* Bishonen: Taiyo
* BoxingLessonsForSuperman: The diving equipment never changes, but the skill and creativity of the characters continually pushes the boundaries of what they can do with it.
* BreakingTheFellowship: The Peru arc splits up the group, leaving Shibuki and Nagisa in Japan while Taiyo and Mio travel to Peru.
* BreakTheCutie: This series hates cute kids, especially younger siblings.
* BrokeEpisode: Quite a number of them actually, and financial stresses frequently drive the decisions that the characters make.
%%* BrokenBird: Machiko.
* BrotherSisterIncest: Narrowly averted between Taiyo [[spoiler:and Mio, who has romantic feelings for him and repeatedly expresses her intent to have his children, but is revealed to be his half-sister in the second-to-last chapter and settles for a platonic relationship with him in the epilogue]].
* ButNotTooForeign: All of Taiyo's love interests turn out to be at least a quarter Japanese.
* CallBack: Several, expecially common when the symbol is concerned.
* CerebusSyndrome: For a manga that started out being about SCUBA Diving and flirting with pretty girls, it got pretty damn dark.
%%* CharacterDevelopment
* ChasteHero: Taiyo isn't asexual, but while he is flirtatious he is very adamant on being exclusively monogamous. Towards the end, when all three of the Miyara sisters admit to having feelings for him he suggests they share him, but is punched out by Mio and Shibuki.
* ChivalrousPervert: Taiyo is a shameless flirt and definitely likes pretty women, but he's dedicated to being faithful to Shibuki and wouldn't dream of taking advantage of a girl or forcing them to do anything against their will. He's also a virgin and in no hurry to have sex.
* ConservationOfCompetence: A few guerrillas manage to give the vastly superior American special forces a good thrashing.
* CorruptTheCutie: Happens to Mio by way of character development.
* CultureClash: Ancient religious traditions and superstitions meet with modern secularism and values.
* CurbStompBattle: The guerrillas decimate the Americans. Also, Taiyo always gets his ass kicked whenever he's in a fight, especially with Martin.
%%* DarkAndTroubledPast: The rule, not the exception.
* DawnOfAnEra: Subverted. The ending ends the cycle of the strange lights and symbols, but the white whale is still very much alive. [[spoiler:At least until the final chapter, where she sacrifices herself to save Taiyo from the US Army's lost nuke. Her calf survives to carry on her legacy.]]
%%* DeathByOriginStory
* DeathGlare: Shibuki is very veeeerrryy good at giving these Taiyo, even after undergoing her ice queen defrosting.
%%* DecadeDissonance
* DefrostingIceQueen: The Miyara sisters and Mar towards Taiyo.
* DelicateAndSickly: Mio, Lago, and Henri are afflicted by a debilitating curse that makes them catalysts for the ruins in their respective regions, which causes them to fall ill repeatedly.
%%* DiabolusExMachina
* DidTheyOrDidntThey: It's all-but outright stated that Taiyo had sex with Mar, but he can't remember the details due to having been drugged.
* DidntThinkThisThrough: The consequences for doing this with SCUBA Diving are lethal.
* DisappearedDad: Kicks off the whole plot. Also the reason why Taiyo is able to spend so much time on Zamimi.
* DisneyDeath: Aida and Professor Muta's ship is destroyed and they are lost at sea, but return later.
%%* DoesThisRemindYouOfAnything
%%* Dojikko: Ai
* DoubleStandardRapeFemaleOnMale: It's strongly implied Mar had sex with Taiyo while he was drugged, against his will, and the manga's ending implies she's pregnant.
* DrivenToSuicide: [[spoiler: The fate of Taiyo's mother, who sacrificed herself to keep her son from dying.]]
%%* DysfunctionJunction
* EldritchAbomination: The white whale is implied to be an AnimalisticAbomination for much of the story, being immortal, supernatural, capable of evading the United States Navy, and seemingly appear anywhere without warning and vanish without a trace. [[spoiler:The last chapter, where she beaches herself to save Taiyo and dies giving birth to a baby white whale, implies this is not the case, though there is definitely something supernatural about her.]]
* EldritchLocation: Deep water, especially caves and the mysterious ruins, are portrayed as this.
* EndOfAnAge: Both globally and for Zamimi.
* EmpathicEnvironment: Kinjou sacrifices Lago during a torrential downpour.
%%* EvilMatriarch: Machiko.
* ExperimentalArcheology: By the US military and Machiko.
%%* FanDisservice: Surprisingly frequent.
* {{Fanservice}}: Quite a lot actually, for both sexes.
* FanservicePack: Mio physically matures quite a bit over the course of the story, due to her entering and progressing through puberty. Taiyo also does this.
* FamilyUnfriendlyViolence: During the Peru arc a soldier is shot by a rebel sniper, and then here is [[spoiler: Lago's death]]
%%* FemmeFatale: Kimjou, among others...
* FilleFatale: Mio tries to seduce Taiyo on multiple occasions despite being several years younger than him.
* ForgotICouldntSwim: Taiyo can't swim at the start of the manga, and learns how to scuba dive over the course of the series.
%%* FourEyesZeroSoul: Machiko Kimjou
%%* FreakOut: Always played for drama.
* FrenchJerk: Henri, but becomes more endearing after some Character Development.
* FreudianTrio: Mio is the maiden, Shibuki is the seductress, and Nagisa is the mother.
%%* GainaxEnding
* GeneralRipper: Jack Reynard seems to be one at first, but he was just following orders and turns out to be a decent guy.
* GenreShift: Starts as a harem comedy and quickly turns into a mystery drama.
%%* GondorCallsForAid: The village.
%%* GoryDiscretionShot: Averted
* GovernmentConspiracy: The US Government has an immense interest in the mystery and ruins.
%%* GratuitousFrench: Henri
%%* GratuitousSpanish
* HandsomeLech: Taiyo's father. [[spoiler:It turns out he's Henri's, Lago's, and Mio's father.]]
%%* HeKnowsTooMuch
* HeWhoFightsMonsters: Overlaps with WellIntentionedExtremist in many cases.
* HitAndRunTactics: The guerrillas and most armed forces in general come out of nowhere and leave just as suddenly.
* HollywoodHealing: Averted when Taiyo and Shibuki get decompression sickness.
* HookerWithAHeartOfGold: Mar Shimabukuro prostitutes herself to get money to look after her little sister.
%%* HonorBeforeReason: Martin
* HostileWeather: The weather does not like to cooperate with anyone.
%%* HumanResources: Literally.
* IAmYourOpponent: Never goes well for Taiyo. He tries to fight twice in the manga. He gets beaten badly both times.
* IDidWhatIHadToDo: Machiko's rationalization [[spoiler: for killing her son and Lago.]]
* ILetYouWin: Martin gives Taiyo the win in their fight for the right to explore Peru's ruined temple... and Mar's hand in marriage.
* IfICantHaveYou: After Taiyo rejects Mio's final attempt to seduce him and stops her from committing suicide, she tries to strangle him.
%%* ImplacableMan: Jack Reynard.
%%* INeedAFreakingDrink: Nagisa, frequently.
%%* InstantWakingSkills: Taiyo
* InterruptedIntimacy: Mio purposely does this any time Taiyo and Shibuki try to get it on.
* InterruptedSuicide: In the final chapter, [[spoiler:Mio tries to drown herself after Taiyo refuses to have sex with her due to her being his half-sister. When he saves her and still rebukes her advances, she tries to strangle him, but comes to her senses and stops.]]
* InTheBlood: Taiyo, Mio, Lago, & Henri are all catalyst [[spoiler:and have the same father]].
* IWillWaitForYou: Shibuki to Taiyo before he and Mio go to Peru.
* JerkWithAHeartOfGold: Mar, Martin, and Kimjou
* JustFollowingOrders: Jack Reynard.
* JustifiedCriminal: Mar is a pickpocket and prostitute in order to get money to look after her sick sister.
%%* KickTheDog
* LadyDrunk: Nagisa gets drunk a lot.
* LightIsNotGood: The glowing sigil that appears on Mio's chest and the chests of several other characters, the luminous ruins, and the spectral white whale associated with them are portents of ill fortune.
* LostTechnology: The technology needed to make the ruins and the symbols work.
* LoveDodecahedron: The Miyara sisters and Mar all develop romantic feelings for Taiyo.
* TheMagicGoesAway: The cycle of the lights and ruins is finally ended. And this is undoubtedly a good thing.
* Magitech: A subtle example with the symbol and the ruins.
* MissingMom: The Miyara sisters lost their mother 10 years before the story starts.
* MoodWhiplash: Big time and right out of nowhere.
* Nosebleed: Happens whenever someone has a reaction to the ruins. Played very seriously in one instance where it is indicative of life-threatening Nitrogen toxicity.
* PastExperienceNightmare: Taiyo has nightmares several times as his trauma-suppressed memories begin returning.
* NoPeriodsPeriod: During the whale watching event Mio falls ill in a way that doesn't involve her curse, and that evening Nagisa sends Taiyo out to pick up some red rice, to his initial confusion.
* OddlyVisibleEyebrows: Pops up with everyone, but is especially noticeable on the non-Japanese characters.
* PillarOfLight: In the shape of a wierd sun/eye symbol.
* PlaceOfPower: There are many of them all over the world.
* ThePlan: The reader is kept on the outside of the various plans.
* PrecociousCrush: Mio develops one on Taiyo that [[ArentYouGoingToRavishMe she makes very explicit multiple times]]. It doesn't go away until the epilogue.
* QuiveringEyes: During the more emotional scenes.
* RescueArc: Played very interestingly in that the goal isn't to physically reclaim anyone, but rather to protect them from harm.
* ReallyGetsAround: It's revealed that Taiyo's father did [[spoiler:and fathered 4 children with 4 different women]].
* RunningGag: Shibuki pulling boxing gloves out of hammerspace and decking Taiyo when he acts perverted. Mio gets in on it in the second-to-last chapter.
%%* SceneryPorn: The diving scenes.
* ShootTheDog: [[spoiler: Machiko shoots and kills Lago]].
* ShownTheirWork: All the stuff about SCUBA Diving. It's heavily detailed to the point that it can get in the way.
* SurpriseIncest: In Chapter 43, [[spoiler:Mio professes to have fallen in love with Taiyo and repeatedly makes romantic advances towards him, though ultimately nothing comes of it. In the second-to-last chapter, Taiyo learns that she is his half-sister, and Mio doesn't react well to the news when she finds out, making one last attempt to seduce him and then trying to drown herself when he refuses. When he saves her, she tries to murder him in a fit of jealous rage.]]
* SurprisePregnancy: It's implied Mar is pregnant with Taiyo's child, as when Machiko activates the temple she feels pain and heat in the vicinity of her uterus.
* TakeThatKiss: When Taiyo starts to own up to inadvertently cheating on Shibuki with Mar, Mio hushes him. When Shibuki demands an explanation, Mio tells her "What happened went something like this," and then kisses Taiyo while smirking at her sister.
* {{Tsundere}}: Shibuki starts off hating Taiyo at the beginning, but slowly and begrudgingly develops feelings for him.
%%* UnnecessaryRoughness
* UnwantedHarem: Taiyo has a number of female characters who want to get in his pants, but is dedicated to Shibuki.
%%* UrbanFantasy
%%* VillainBall: When people pick this up, they do not like to let go.
%%* WellIntentionedExtremist: Several
%%* WhyDontYouJustShootHim
* YouCantFightFate: Machiko's view, which leads to ShootTheDog