Dolphin Rider Koishi

A finished Web Serial Novel which follows alternate versions of Touhou characters in a Magical Girl Warrior story. It's better than it sounds, with well-expressed characters and creative reinterpretations of Canon and Fanon elements. The complete version can be read here, with a less complete version readable on Fanfiction.net.

In the coastal Japanese city of Gensoutou, Ordinary High School Student 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 strange jewel materialises out of thin air, and she's attacked by Fish People 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 "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 Warrior Therapist, recruiting Sirens and curing Monsters of the Week by forcing them to confront their psychological issues.

See Touhou for tropes carried over from canon.

"Mama’s just sleeping Papa didn’t do anything to her"
 * Adaptational Villainy: Rinnosuke Morichika goes from eccentric shopkeeper to ruthless mob boss. Also Jozu, who was far more timid in the (unrelated) fic she debuted in.
 * Adaptation Dye Job: Being an Urban Fantasy setting, most characters have more mundane hair colours than they did in the source material, except when they're using magic. The first sign of Koishi's magical potential is that she can catch glimpses of characters' "magic hair".
 * Alternate Universe Fic
 * Amnesiac Hero: Sakuya
 * Actually Not a Vampire: Remilia and Flandre actually suffer from Xeroderma pigmentosum, though Remilia pretends to be a vampire as a coping mechanism (Flandre does not).
 * A Day in the Limelight: 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 shows up for a cameo, and Marisa has not appeared.
 * Amoral Attorney: Reimu
 * Angst Aversion: Patchouli would like to have a few choice words with anyone who insists that True Art Is Angsty.
 * Artificial Gill: The "Rings of Breath".
 * Atlantis Is Boring: Averted. Youkai society is dominated by sea-dwellers due to their greater population and lower need to hide from humans.
 * The Atoner: Nitori, for her role in creating The Ravager.
 * Author Appeal: The writer is rather fond of the aquatic.
 * And swimsuits. Lots and lots of swimsuits.
 * Battle in the Center of the Mind: This is essentially Koishi's power.
 * Becoming the Mask:
 * Bloody Murder/Cast from Hit Points: The latent powers of
 * Brainwashed and Crazy: Characters affected by the Mindcoils.
 * By the Power of Grayskull: Each of the Sirens must recite a unique poem to transform.
 * Calling Your Attacks
 * Card Sharp: Sakuya and Tewi.
 * Chaste Hero: Koishi. The trope page is even potlinked.
 * The Chosen One: The Sirens.
 * Combo-Platter Powers: The Sirens, who unlock their own latent powers in addition to gaining Magical Girl powers.
 * Composite Character:
 * Consummate Liar: Tewi
 * Disco Dan: Iku
 * Drives Like Crazy: Meiling
 * Dumb Blonde: Sakuya exploits this by dying her hair to seem less suspicious.
 * Energy Absorption: can absorb magical attacks, which acts as a power source for her stronger abilities.
 * Epiphany Therapy: Most characters have some kind of psychological issue they must overcome before they can use their powers or be cured of a Mindcoil.
 * Escapism: Flandre and Patchouli have a secret love of Magical Girl manga for this reason.
 * Everybody Hates Mathematics
 * Everyone Is a Super: Everyone was a super. See Heroic Sacrifice.
 * Fake American: Sakuya
 * Fantastic Fighting Style: Flowing Tide (a soft style used by the White Pearl), and Crashing Wave (a hard style used by the Black Claw).
 * Fish Out of Water: Sango is a near-literal example, being a dolphin with limited knowledge of human customs.
 * Follow in My Footsteps: Kaguya's father, who expects her to be a brilliant pharmacist.
 * Freudian Excuse: Tewi became a compulsive liar from having to lie to herself.

"It hurt. It hurt like hell. She didn't care, she just wanted this thought to go away. The more she looked at that face, the less Kaguya looked like a heartless monster, and the more she looked like a stupid girl who made a stupid choice to win over her daddy.
 * The Gambler: Sakuya
 * Glamour Failure: Most youkai retain some traits of their animal selves in human form, such as Sango's dorsal fin, which they must hide by conventional means.
 * Goggles Do Something Unusual: Koishi gets some glasses which block her ability to see the magic world. Later she upgrades to contacts which can be turned off at will.
 * Gone Horribly Right: When the youkai were losing their ancient war against humanity their last resort was to unleash Project 046, aka The Ravager, a creature which single-handedly defeated the armies of mankind. And then didn't stop.
 * Gratuitous French: 's transformation phrase.
 * Healthcare Motivation: Sakuya has spent years trying to find a cure for the Scarlets' XP, despite it being a genetic condition and inherently incurable.
 * The Heart: Koishi
 * Here There Were Dragons
 * Heroic Sacrifice: In the backstory, sealing The Ravager required the human race to sacrifice its knowledge of magic, and Yukari Yakumo to sacrifice her life.
 * He Who Fights Monsters: Mokou trained Cirno to defend herself from bullies, but she ended up becoming the leader of the bullies.
 * Heroic Albino: Remilia and Flandre. Technically it's Xeroderma pigmentosum rather than albinism, but the effect is similar.
 * Humans Are Average: Humans' magic powers are generally weaker than those of youkai, but far more varied.
 * Humans Are Flawed
 * How Do I Shot Web?: (and possibly Koishi) were initially using their powers subconsciously, unaware that they had them.
 * If It Tastes Bad, It Must Be Good for You: Mokou's health food tastes disgusting.
 * If Jesus, Then Aliens: After running into so many youkai, Koishi immediately believes Remilia when she claims to be a vampire. Sango has to inform her that vampires don't exist.
 * I Just Want to Be Normal: Flandre. Her inability to accept her XP is her form of "madness" in this universe.
 * Ill Girl: The Scarlet sisters.
 * In the Name of the Moon: The Sirens tend to do this involuntarily while transformed, much to their confusion.
 * Invisible to Normals: Everyone has a "magical appearance" which most people can't see.
 * I Reject Your Reality: Multiple characters have this issue, most notably Tewi.
 * Irrational Hatred: Mokou.

She didn't want Kaguya to have an explanation. Explanations meant she'd need to accept that she had a reason for screwing her over beyond being a heartless bitch, and then she'd have to let the grudge go. But forgiveness was hard, so much harder than just staying angry."

"Nitori typed in the name lazily. They had to settle for the family name, Scarlet, mainly because all of them found the name Flandre so foreign they had no clue how to spell it."
 * Is It Something You Eat?: "...What's a haiku? Sounds like a nice topping to me."
 * Karma Houdini: Rinnosuke literally gets away with murder, by bribing or discrediting everyone connected to any charge brought against him. He's not a Villain with Good Publicity; everyone knows he's The Don, they just can't do anything about it.
 * Knight Templar:
 * Laser-Guided Amnesia: Curing 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.
 * Light-Haired Swimmer: Koishi and Sango are the characters who spend the most time in water, and both have silver hair at all times.
 * Little Miss Con Artist: Tewi
 * Locked Into Strangeness: The reason for Koishi's silver hair.
 * Magical Girl Warrior
 * The Masquerade: Maintained in order to prevent humans from destroying themselves through magical warfare.
 * Mineral MacGuffin: The Tidal Teardrops.
 * Monster of the Week: Humans who have been brainwashed by the Black Claw, and given Black Keys (not that kind) which let them transform into a One-Winged Angel.
 * Mooks: The fishmen who explode into fish when killed.
 * Mundane Utility: Stopping time is quite useful when gambling.
 * Near-Death Experience: 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 (causing her powers to mutate) and turning her hair silver.
 * Next Episode Preview/Omake: Faithfully recreated from its Magical Girl anime inspirations.
 * Obfuscating Stupidity:
 * Open-Heart Dentistry: Patchouli is a geneticist, but accepted a probably-misinformed request to work as the Scarlets' obstetrician because it payed well (and her own poor health made it hard to find work in her actual field).
 * Ordinary High School Student
 * Original Characters: 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).
 * Phantom Zone: Watery ones are used by magic-users for duels.
 * Playboy Bunny: Koishi and her allies are forced to dress up like this to infiltrate a casino.
 * Playful Hacker: "Princess" Kotohime.
 * Politically-Motivated Teacher: Keine
 * Pothole: Freqently used to link to pictures, background music or trope pages.
 * Power Dyes Your Hair To The Color It Had In Canon
 * Power Strain Blackout:
 * Proud Warrior Race Guy: Jozu, the race in question being "shark". Sango to a lesser extent.
 * Rank Inflation: Nitori has a confusing set of power ranks for magic-users which includes "B", "S+" and "XS+++".
 * Refusal of the Call
 * Renaissance Man: "Kawashiro Nitori. Physics professor. Magical cult leader. Bartender...?"
 * Replacement Goldfish:
 * Rousseau Was Right
 * Self-Duplication: Tewi's latent power.
 * She Is Not My Girlfriend: Koishi, in regards to Sango.
 * Shrouded in Myth: Yukari Yakumo. Even her species was a mystery.
 * Single-Issue Psychology: Played straight by most characters, though Sakuya has at least two unrelated issues.
 * Speaks Fluent Animal: Koishi's power lets her communicate telepathically with youkai, regardless of form.
 * Spell My Name with an "S": ZUN's inconsistent spelling of Flandre/Frandle/Frandoll Scarlet is referenced.

""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. You’re telling me that you’d rather I had to go through a lockpicking charm every time I wanted to get in here after hours? Jeez, and you say that I’m crazy.""
 * Spy From Weights and Measures: Nitori runs numerous service organisations as fronts for the White Pearl, allowing her to infiltrate agents into almost any location or private event. The Black Claw does similarly.
 * Stepford Smiler: Kaguya
 * Stock Animal Diet: Being a dolphin, Sango greatly prefers fish (particularly mackerel) to all other foods and will often extol its virtues.
 * Superpowerful Genetics: All humans have latent magic powers which can be guessed from their heritage.
 * Take a Third Option: When someone is Mindcoiled, normally the choice is to leave them Brainwashed and Crazy or kill them. Koishi instead chooses to engage in a Battle in the Center of the Mind to destroy the Mindcoil.
 * Teen Genius: Mokou, but only when it comes to chemistry or biology.
 * There Are No Therapists
 * This Is My Name on Foreign: As a Fake American, Sakuya Izayoi uses the pseudonym "Luna Fullerton".
 * Utility Magic: Exists, but isn't used much.

""And what's life like in the real world? Well, imagine 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 - crazy hair, weird eye colours, and in your case 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.""
 * Verbal Tic: Sango has one, phwee~. She actually does it on purpose as a form of magic sonar, and drops it when not needed.
 * Virtual Soundtrack
 * Warrior Therapist: Koishi.
 * Water Is Air: "And of course, all of this was fire was being lit underwater. Sometimes Koishi wished magic could at least make the tiniest bit of sense."
 * Weapon of Choice
 * Prongs of Poseidon/Whip It Good: Koishi
 * Bare-Fisted Monk:
 * Death Dealer:
 * Hand Cannon:
 * Web Serial Novel
 * Weirdness Censor: See Heroic Sacrifice.
 * Weirdness Censor: See Heroic Sacrifice.


 * "Well Done, Son" Guy: Kaguya's father has very high expectations of her which she struggles to live up to. The Kaguya/Mokou feud actually started when she stole from Mokou to please him, and Kaguya is implied to feel extremely guilty about it.
 * Worthy Opponent: Jozu to Sango.
 * You Can See Me?: