An ongoing WebSerialNovel which follows [[AlternateUniverseFic alternate versions]] of ''VideoGame/{{Touhou}}'' characters in a MagicalGirlWarrior story. Better than it sounds, with well-expressed characters and creative reinterpretations of {{Canon}} and {{Fanon}} elements. Can be read [[http://www.shrinemaiden.org/forum/index.php/topic,6913.0.html here]], with [[http://www.fanfiction.net/s/7082391/1/Dolphin_Rider_Koishi a less complete version]] readable on FanFictionDotNet. Finally completed on 24 November 2013 after three long years.

In the coastal Japanese city of Gensouto, OrdinaryHighSchoolStudent Koishi Komeiji has been living alone for the last few months (apart from her pet cat and raven) since her sister Satori vanished without a trace. Bullied and lonely, when she hears a rumour about an abandoned shrine that grants wishes, she begs for someone strong and brave to look after her. Instead a [[MineralMacGuffin strange jewel]] materialises out of thin air, and she's attacked by FishPeople only to be saved by a talking dolphin. The dolphin tells Koishi to squeeze the jewel, and she defeats the fishmen by transforming into the [[MagicalGirl "Siren"]] Dolphin Rider Koishi. Back at her apartment the now-human dolphin explains that she is a youkai, and a junior member of a human-protecting organisation called the Order of the White Pearl. Koishi and the dolphin (named Sango) must find the remaining six Sirens before the White Pearl's enemies, the Children of the Black Claw, can use their powers for evil.

Along the way Koishi ends up as a sort of WarriorTherapist, recruiting Sirens and curing MonstersOfTheWeek by forcing them to confront their psychological issues.

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See ''VideoGame/{{Touhou}}'' for tropes carried over from canon, and the [[Characters/DolphinRiderKoishi character sheet]] for character-specific tropes.

!!Tropes in ''FanFic/DolphinRiderKoishi'' include:

* AdaptationalVillainy: Rinnosuke Morichika goes from eccentric shopkeeper to [[TheDon ruthless mob boss]]. Also [[OriginalCharacter Jozu]], who was far more timid in the (unrelated) fic she debuted in.
* AdaptationDyeJob: Being an UrbanFantasy setting, most characters have more mundane hair colours than they did in the source material, [[PowerDyesYourHair except when they're using magic]]. The first sign of Koishi's magical potential is that she can catch glimpses of characters' "magic hair".
* AlternateUniverseFic
* ActuallyNotAVampire: Remilia and Flandre actually suffer from [[http://en.wikipedia.org/wiki/Xeroderma_pigmentosum Xeroderma pigmentosum]], though Remilia pretends to be a vampire as a coping mechanism ([[IJustWantToBeNormal Flandre does not]]).
* ADayInTheLimelight: While most of the Windows and PC-98 cast appear to exist in some form, the protagonist is Koishi, who has never been a playable character. Reimu only appears as a minor character, and Marisa has only been mentioned in a single line of throwaway dialogue.
* ArtificialGill: The "Rings of Breath".
* AtlantisIsBoring: Averted. Youkai society is dominated by sea-dwellers due to their greater population and lower need to hide from humans.
* AuthorAppeal: The writer is rather fond of the aquatic.
** And swimsuits. Lots and lots of swimsuits.
* BattleInTheCenterOfTheMind: This is essentially Koishi's power. [[spoiler: Ironically, she undergoes a more literal example while BrainwashedAndCrazy]]
* BloodyMurder[=/=]CastFromHitPoints: The latent powers of [[spoiler:the Scarlet family.]]
* BrainwashedAndCrazy: Characters affected by the Mindcoils.[[spoiler: These included Cirno, Tewi, Eiki, Yuyuko, and Koishi herself]]
* ByThePowerOfGrayskull: Each of the Sirens must recite a unique poem to transform.
* CallingYourAttacks
* CardSharp: Sakuya and Tewi.
* TheChosenOne: The Sirens.
* ComboPlatterPowers: The Sirens, who unlock their own latent powers in addition to gaining MagicalGirl powers.
--> In order:
** Koishi: Invoking BattleInTheCenterOfTheMind [[spoiler: and subconscious manipulation, MakingASplash]]
** Siren#2 [[spoiler:Mokou: Resurrection, PlayingWithFire]]
** Siren#3 [[spoiler:Sakuya: TimeStandsStill, CardSharp]]
** Siren#4 [[spoiler:Komachi: SpaceMaster, BFG]]
** Siren#5 [[spoiler:Youmu: DopplegangerAttack, SwordBeam]]
** Siren#6 [[spoiler:Nazrin/Shou: PowersAsPrograms, PowerArmor]]
** Siren#7 [[spoiler:Satori: {{Telepathy}}, ShockAndAwe]]
* DistantFinale: As a result of [[spoiler:Koishi being in a coma for two years after the final battle.]]
* EpiphanyTherapy: Most characters have some kind of psychological issue they must overcome before they can use their powers or be cured of a [[BrainwashedAndCrazy Mindcoil]].
* EverybodyHatesMathematics
* EveryoneIsASuper: Everyone ''[[HereThereWereDragons was]]'' a super. See HeroicSacrifice.
* FantasticFightingStyle: Flowing Tide (a soft style used by the White Pearl), and Crashing Wave (a hard style used by the Black Claw).
* GlamourFailure: Most youkai [[LittleBitBeastly retain some traits of their animal selves in human form]], such as Sango's dorsal fin, which they must hide by conventional means. [[spoiler: Upon death, these are the first features to fade away.]]
* GogglesDoSomethingUnusual: Koishi gets some glasses which [[PowerLimiter block her ability to see the magic world]]. Later she upgrades to contacts which can be turned off at will. [[spoiler: Nazrin's Ghost Rat Protocol grants her a visor with a HeadsUpDisplay]]
* HereThereWereDragons
* HeroicSacrifice: In the backstory, [[SealedEvilInACan sealing The Ravager]] required the human race to [[HereThereWereDragons sacrifice its knowledge of magic]], and Yukari Yakumo to sacrifice her life.
* HumansAreAverage: Humans' magic powers are generally weaker than those of youkai, but far more varied.
* HumansAreFlawed: [[spoiler: A big reason behind Satori's FaceHeelTurn]]
* HowDoIShotWeb: [[spoiler:Sakuya and Komachi]] (and possibly Koishi) were initially using their powers subconsciously, unaware that they had them.
* IfJesusThenAliens: After running into so many youkai, Koishi immediately believes Remilia when she claims to be a vampire. [[ActuallyNotAVampire Sango has to inform her that vampires don't exist.]]
* InTheNameOfTheMoon: The Sirens tend to do this involuntarily while transformed, much to their confusion.
* InvisibleToNormals: Everyone has a "magical appearance" which most people can't see.
* IRejectYourReality: Multiple characters have this issue.
* IsItSomethingYouEat: "...What's a haiku? Sounds like a nice topping to me."
* KarmaHoudini: Rinnosuke literally gets away with murder, by [[EveryManHasHisPrice bribing]] or discrediting everyone connected to any charge brought against him. He's not a VillainWithGoodPublicity; everyone knows he's TheDon, they just can't do anything about it. [[spoiler: until he [[YouHaveOutlivedYourUsefulness outlives his usefulness and is shot]]]]
* LaserGuidedAmnesia: Curing [[BrainwashedAndCrazy the victim of a Mindcoil]] leaves them with only a general recollection of their actions, erasing any information on magic. The White Pearl can also create this effect on purpose.
* LightHairedSwimmer: Koishi and Sango are the characters who spend the most time in water, and both have silver hair [[LockedIntoStrangeness at all times]].
* MagicalGirlWarrior: Every Siren.
* TheMasquerade: Maintained in order to [[HumansAreTheRealMonsters prevent humans from destroying themselves through magical warfare]]. [[spoiler:Became in danger of being broken due to the zoo incident, and [[TheUnmasquedWorld completely destroyed]] in the finale.]]
* MineralMacGuffin: The Tidal Teardrops.
* MonsterOfTheWeek: Humans who have been brainwashed by the Black Claw, and given "Black Keys" ([[{{Nasuverse}} not that kind]]) which let them transform into a OneWingedAngel.
* {{Mooks}}: The [[FishPeople fishmen]] who explode into fish when killed.
* MundaneUtility: [[TimeStandsStill Stopping time]] is quite useful [[CardSharp when gambling]].
* NearDeathExperience: Can partially awaken a person's latent magic powers. Koishi had one of these in her backstory, with the side effects of closing her third eye ([[RePower causing her powers to mutate]]) and [[LockedIntoStrangeness turning her hair silver]].
* NextEpisodePreview[=/=]{{Omake}}: Faithfully recreated from its MagicalGirl anime inspirations.
* OrdinaryHighSchoolStudent: Several of the cast.
* OriginalCharacters: Sango Tororetsu and Jozu Manou, dolphin and shark youkai respectively, both of whom debuted in non-AU fic by the same author (though Jozu's personality is quite different).
* PhantomZone: Watery ones are used by magic-users for duels.
* PlayboyBunny: Koishi and her allies are forced to dress up like this to infiltrate a casino.
* PotHole: Freqently used to link to pictures, [[VirtualSoundtrack background music]] or [[TVTropesWillRuinYourLife trope pages]].
* PrecisionFStrike: [[spoiler: When Komachi frees Ran from Mamizou's seal]]
* [[PowerDyesYourHair Power Dyes Your Hair To The Color It Had In Canon]]; and even if this trope isn't currently in effect, odds are the girl(s) in question will still have artificial highlights.
* RankInflation: Nitori has a confusing set of power ranks for magic-users which includes "B", "S+" and "XS+++".
* RousseauWasRight
* SingleIssuePsychology: Played straight by most characters, though Sakuya has at least two unrelated issues.
* [[spoiler: SadisticChoice: The blade Aptera was created by Yukari to destroy the Ravager, but requires an entire race's worth of magic to use. Draining either the magic of all humans or all youkai would seemingly lead to disaster in either case. Koishi works out how to TakeAThirdOption.]]
* [[spoiler: SoulJar: Teardrops can act like them, as in the case of Shou.]]
* SuperpowerfulGenetics: All humans have latent magic powers which can be guessed from their heritage.
* TakeAThirdOption: When someone is Mindcoiled, normally the choice is to leave them BrainwashedAndCrazy or [[MercyKill kill them]]. Koishi instead chooses to engage in a BattleInTheCenterOfTheMind to destroy the Mindcoil. [[spoiler:Though Nitori believes that attempting this on the wrong person could get Koishi killed.]]
** [[spoiler:Powering Aptera without draining an entire race of magic... by using the {{Masquerade}} instead.]]
* ThereAreNoTherapists: Iku, the school nurse, sort of acts as one, but there are no actual therapists in story.
* [[spoiler:TheUnmasquedWorld: The result of using the masquerade to power Aptera.]]
* UtilityMagic: Exists, but isn't used much.
-->"Koishi-san, let me get this straight. You humans have invented a system that lets you cut spare keys to any door. No fuss, no pizazz, no evidence. Youre telling me that youd rather I had to go through a lockpicking charm every time I wanted to get in here after hours? Jeez, and you say that Im crazy."
* VirtualSoundtrack
* WaterIsAir: "And of course, all of this fire was being lit underwater. Sometimes Koishi wished magic could at least make the tiniest bit of sense."
* WeaponOfChoice
** ProngsOfPoseidon[=/=]WhipItGood: Koishi. [[spoiler:Her SuperMode instead uses [[HeroesPreferSwords a sword]]]]
** HeroesPreferSwords: [[spoiler: Satori, Koishi's [[MidSeasonUpdgrade Ocean Princess form]]]]
** BareFistedMonk: [[spoiler:Mokou]]
** DeathDealer: [[spoiler:Sakuya]]
** HandCannon: [[spoiler:Komachi]]
** [[spoiler:DualWielding: Youmu, Nazrin]]
* WebSerialNovel
* WeNeedADistraction: [[spoiler: During the fight between Nazrin, Mamizou, and Komachi, Nazrin was the distraction]]
* WeirdnessCensor: See HeroicSacrifice.
-->"And what's life like in the real world? Well, imagine [[EveryoneIsASuper everyone you ever knew had some sort of superpower or magical ability]]. Everyone in your class is some sort of {{magical girl}}, and they all look like it as well - [[YouGottaHaveBlueHair crazy hair]], [[TechnicolorEyes weird eye colours]], and in your case [[ThirdEye an extra eye on top of the two you've already got]]. But again, no-one realises it, so all of that magic just goes to waste."
* [[spoiler: YouHaveOutlivedYourUsefulness: Rinnosuke]]