[[http://www.fimfiction.net/story/48739/harmony-theory Harmony Theory]] is a MyLittlePonyFriendshipIsMagic fanfic by Sharaloth.

After the defeat of Chrysalis, Celestia assigns Twilight the task of studying The Elements of Harmony. Over a thousand years later, Rainbow Dash wakes up underground, next to a dead stallion, with no memory of anything that has happened since Ponyville was assigned tornado duty, in a world very different to the one she is used to. Equestria has split in two, the magic of the world has faded, the geography, cultures and languages are not what she is familiar with and the first thing she does gets her in trouble with the Lunar Republic's police force.

After injuring herself, she is rescued by [[BadassBookworm Star Fall/Fallen Star]] and her griffon bodyguard Astrid, two spies for the Solar Kingdom. Star Fall recognises the language Rainbow speaks as Old Equestrian, that she is the most powerful and magical pegasus to have been seen in at least eight hundred years and that she is claiming to be the ancient hero Rainbow Dash.

The tensions between the two sides of Equestria only increase with the arrival of a living superweapon and it looks like Nightmare Umbra, the alicorn of war is set to return. And what does Rainbow's arrival have to do with the activities of the criminal Max Cash?

And how does all this relate to Twilight's disturbing discoveries about the Elements of Harmony themselves?

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!!This fanfic contains examples of the following tropes:

* TheAce: Rainbow Dash and [[spoiler: Applejack]]. This is due to their vast amount of innate magic, which the ponies of future Equestria have little of. Twinkle Shine even comments that Rainbow Dash was a phenom even by pre-Schism standards.
* AfterTheEnd: The Schism was an apocalyptic event which resulted in this.
* ArrangedMarriage: The griffons and changelings have eugenics programs. The Solar King also has the power to arrange this. [[spoiler: He uses this power to betrothe Star Fall to his son]].
* BadFuture: What Rainbow Dash finds herself in. While not dystopian, it's still bad compared to her Present Day. [[spoiler: Applejack and Rarity finds themselves there, too, whilst Spike is still alive]].
* BadassBookworm: Star Fall is a scholar, magic talent, spy and powerful (by modern standards) mage, able to use her abilities in a fight.
* BadassGrandpa: [[spoiler: Spike is one, having reached the present day "the long way around". The little baby dragon is now one of the biggest adult dragons still alive on the planet, and with a huge amount of political influence if he deigns to use it.]]
* BladeOnAStick: Melody chooses a spear in her fight against [[spoiler: Charisma]].
* BlessedWithSuck: Charisma's Cutie Mark decreed special talent: she's a born assassin. As a result, she constantly "hears" her subconscious not only whispering ''how'' she can kill every single being she interact with, but demanding that she ''does'' kill them. It goes without saying that this has driven her totally insane.
* BloodKnight: Charisma's talent actually encourages her to fight. And she really enjoys it.
* [[BreedingCult Breeding]] [[ThePlan Plan]]: The Solar King is bent on having powerful Royal Heirs to the point[[spoiler: that he wants an Alicorn born into the family. And he believes Star Fall is the key to this]]. So far, nopony else is in agreement with him, but nopony is able to change his mind
* CharmPerson: Max Cash, who uses a combination of ArmorPiercingQuestion and BreakThemByTalking to compel his victims into performing, as he calls it, "One. Little. Betrayal." [[spoiler:Him using an Inverted Element of Loyalty helps.]]
* CloudCuckooLander: Blaze's speeches are enough to make some fans suspect him to be Pinkie's descendant.
* CuteAndPsycho: Charisma is a pretty pink pegasus who is considered very attractive. She's also [[AxCrazy dangerously insane]].
* DeadpanSnarker: Astrid telling Star that she [[SarcasmMode regrets becoming an "unstoppable badass" instead of learning "egghead language"]] shows her to be this.
* TheDreaded: Charisma is basically considered impossible to beat in single combat and scares just about everyone who knows about her. Nightmare Umbra is even scarier as she's effectively a war goddess ponification of destruction.
* DidYouJustPunchOutCthulhu: Rainbow, Astrid and Star Fall actually manage to [[spoiler: chase off Nightmre Umbra. However, Umbra is still regaining her strength.]]
* DoesNotKnowHisOwnStrength: A variation. Rainbow ''does'' know how strong she is. What she doesn't realise at first though is how fragile everypony ''else'' is and nearly kills two police officers by accident. Even the air pressure from her sonic booms are dangerous.
* FantasticSlur: "Insect" for changeling. Also [[NicknamingTheEnemy the two sides of Equestria call each other "lunatics" and "sun-heads".]]
* FauxAffablyEvil: Max Cash can act rather polite and friendly. But it has a disturbing undercurrent. He [[EvilCannotComprehendGood barely understands friendship]] and basically is just messing with heads. While not confirmed by the writer, a lot of Max's actions are similar to the characteristics of actual sociopaths.
* GeniusLoci: The Everstorm seems sentient and malevolent.
* {{Gotterdammerung}}: Celestia and Luna are now [[spoiler: sealed in their respective celestial bodies]]. As a result, this has sapped ambient magic, causing the present day population of ponies to be dramatically weaker than those of the eras before.
* HermeticMagic: As a pegasus, Star Fall has no horn and so casts spells by drawing magic circles on spell paper.
* HealingFactor: Nightmare Umbra regenerates almost instantly from injury, [[MadeOfIron assuming you can get through her defenses]]. Her [[BloodyMurder blood fights back as well.]] Rainbow also heals extremely quickly to the point that when Star Fall boosted her HealingFactor her wounds began closing up before their eyes.
* ImpossibleTask: The Maul is an obstacle course designed to be impossible to complete which is used in training Solar Kingdom spies. [[spoiler: Rainbow completed it, but with a lot more difficulty than she expected as she didn't realise that she'd have to be dodging bullets, missiles and melee fighters at the time.]]
* InLoveWithYourCarnage: After Charisma sees what Rainbow can do, she seems impressed and starts calling her [[TermsOfEndangerment "Hot Stuff"]]. She is also pleased by Blaze's resistance to torture.
* InterplayOfSexAndViolence: Charisma is sometimes turned on by the idea of others being injured.
* InUniverseNickname: Blaze for Trail Blazer.
* IWantMyJetpack: Rainbow actually asks why they don't have jetpacks. Star Fall is actually a bit disappointed at how unimpressed Rainbow seems with the future.
* KnifeNut: Charisma raids Melody's weapons. Naturally, it's the knives she takes.
* {{Knighting}}: [[spoiler: Rainbow Dash]] gets knighted after helping defeat [[spoiler: Nightmare Umbra.]] However this is done not as a reward, but as a political tactic to draw attention away from [[spoiler: Star Fall's engagement to the prince.]] In this universe, knighthood is another form of nobility, and giving the knight an estate to manage is included in the ceremony.
* LightningBruiser: Rainbow is faster, stronger and tougher than pretty much every modern pony. There ''are'' modern supersonic pegasi, but they are [[FragileSpeedster extreme specialists]] and only the more powerful earth ponies are stronger or tougher (and probably not both).
* LivingLieDetector: Hard Boiled's magic lets him function as one of these.
* LivingStatue: [[spoiler:Apparently Rainbow Dash, Applejack, Rarity, and presumably the rest of the Mane 6 are animate sculptures who possess their respective consciousness from different periods of time.]]
* TheMagicGoesAway: The Schism [[spoiler: as part of Celestia and Luna's plan.]] This has had severely negative effects on the planet; for example, all ponies are vastly inferior in ability compared to what Rainbow Dash [[spoiler: and the other members of the Mane Six]] remember being capable of, whilst the griffons have nearly gone extinct due to the low magic levels impacting on their genetic viability.
* MakeMeWannaShout: Nightmare Umbra uses the Royal Canterlot Voice as a weapon. Sonic booms can also be weaponised.
* ManipulativeBastard: Max Cash with a little help from [[spoiler: a couple of Elements of Harmony]].
* TheMentor: Twinkle Shine for Star Fall.
* MindControl: Both an ability used by the changelings and [[spoiler: an ability Max Cash is using the Elements of Harmony for.]]
* MotorMouth: Blaze really seems to like talking.
* MySpeciesDothProtestTooMuch: [[DownplayedTrope Downplayed.]] Calumn has an existential crisis about his identity as a changeling and what that means, but changelings do not seem to be AlwaysChaoticEvil in this fic. Just [[BlueAndOrangeMorality different]].
* NotQuiteFlight: Bigwig can levitate platforms to carry himself at speeds rivaling pegasi (though with worse maneuvrability).
* OutgrownSuchSillySuperstitions: [[InvertedTrope Inverted.]] Modern Equestria is both more scientifically advanced ''and'' more religious than Rainbow is used to. She considers it strange to think of the alicorns as gods or to pray to them. Twinkle Shine lampshades how this is different from what her class might expect.
* PainfulTransformation: [[spoiler:How Twinkle Shine transforms into Nightmare Umbra is...not pleasant. It involves her bones, tendons, and flesh constantly shifitng breaking and tearing and healing as she grows wings and more than doubles in size.]]
* ThePowerOfFriendship: As one might expect for a MyLittlePonyFriendshipIsMagic fic, this turns up. But things are more complicated than you would normally expect from the trope.
* PsychicAssistedSuicide: [[spoiler: Max Cash can do this to the unconnected.]]
* PsychoExGirlfriend: Charisma is [[spoiler: Trail Blazer's]] ex.
* PunctuatedPounding: Rainbow does this to the thugs who were torturing Blaze and tried to do the same to her.
* RealityIsOutToLunch: The Everstorm induces insanity, creates illusions, moves locations, has variable gravity, logic defying weather, attacks with floating skulls and the occasional crucified zombie ursa major animated by fast growing vines among other things.
* ReasonableAuthorityFigure: Bigwig is considered a fair employer and is effective in helping calm a potential mob, [[spoiler: until Charisma intervenes.]]
* RedBaron: Charisma is called "The Asskicker" by her enemies. Also, "The Killer".
* RetiredBadass: Bigwig is former milliatary and can fight ''[[TheDreaded Charisma]]''.
* SecretIdentity: Rainbow's is [[MythologyGag Firefly]].
* SemanticSuperpower: Rainbow is able to use her talent of being fast and winning to win a bet and learn how to speak Solar in mere days. [[spoiler: Or she might be mistaken after all.]]
* ShapeshiftersDoItForAChange: Changelings take full advantage of the fact that their VoluntaryShapeshifting let's them switch gender at will. They do have a default gender though.
* [[ShowWithinAShow Book Within A Fic]]: ''Harmony Theory'' itself and ''The Magic of Friendship''. Both by Twilight.
* SlaveRace: Every griffon is pledged to serve the Solar King, as his magic is keeping their species from extinction.
* SuperSoldier: How Rainbow is viewed by those in the setting.
* TactfulTranslation:
-->'''Rainbow:''' Buck you, Bird Brain!
-->'''Astrid:''' What did she say?
-->'''Star Fall:''' She says that she's unhappy, but will accept the wisdom of your decision.
* TortureTechnician: Charisma and she enjoys it.
* TranslationConvention: There are at least three languages in the fic. All three are represented by English in the fic. A switch in languages is represented by writing the language which is spoken less in that scene in italics.
* UnskilledButStrong: Astrid claims that Rainbow is this. Gamma responds that the problem isn't that Rainbow is unskilled, but rather that she's a TechnicalPacifist.
* WalkingArmory: How Bigwig chooses to confront Charisma.
* WarGod: Nightmare Umbra is thought of this way. But she is feared rather than worshipped.
* WillingChanneler: Nightmare Umbra is possessing the willing [[spoiler: Twinkle Shine]].
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