[[http://www.fimfiction.net/story/48739/harmony-theory Harmony Theory]] is a ''WesternAnimation/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 recognizes 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 [[spoiler:,Applejack and Rarity]]. 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]].
* TheAssimilator: Nightmare Umbra can absorb the ashes of the fallen to increase her strength, and she can summon anyone she had absorbed as an undead minion.
-->'''Nightmare Umbra''': Burn, Fallen Star. Burn And Become One With Me.
* BadFuture: What Rainbow Dash finds herself in. While not dystopian, it's still bad compared to her Present Day. [[spoiler: Applejack and Rarity find themselves there, too, whilst Spike is still alive]].
* BadassBoast: Nightmare Umbra gives these a lot. Examples:
-->"Beaten? No. At My Weakest I Fought Three Of Your Best, And They Did Not Impress. The Student Who Thinks Herself A Princess? Her Magic Could Not Match Mine. The Soldier Who Forsakes Duty? Her Fury Was But The Wind, Its Might Spent On Empty Bluster. The Hero A Thousand Years From Home? She Was The Only One Who Could Challenge Me, And Even She Fell To My Power."
-->"So Be It. If A Thousand Stand Together, Then Together A Thousand Will Fall."
-->"There Is No Escape. There Is No Victory. There Is Only Me. And Death."
* 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.
* EternalEnglish: Averted. Although the languages that the two sides speak are based off of Old Equestrian, neither one can be understood by Rainbow Dash at first. That and, like real languages, Solar and Lunar are different enough that understanding one doesn't mean you understand the other.
* FantasticRacism: Most ponies have serious hatred of changelings and in the Solar Kingdom there is a strong belief in the supremacy of unicorns over other kinds of ponies. [[spoiler: It leads to some political uncertainties and a lot of angry nobles the moment the king announces that Star will marry one of his sons, who he also makes his heir to the throne]].
* 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.
* GreyAndGrayMorality: Neither the Solar Kingdom or Lunar Republic are exactly bad, both have some unpleasant parts to them and neither is really that wrong for seeing the other as a serious threat. The only black so far seems to be Cash and Nightmare Umbra, a criminal with way too much power and an immortal alicorn that causes a lot of destruction. [[spoiler: And that last one may have some goal in mind that is intended to help the world.]]
* HarmfulHealing: Healing magic caries a high risk of causing cancer, so most avoid using it unless they have no choice.
* 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.
* {{Hellfire}}: Nightmare Umbra controls Ashfire. One touch and it consumes you until nothing is left but ash, and it is almost impossible to extinguish. [[spoiler:It feeds on magic. Star Fall is able to survive it by redirecting her internal magic away from it, so it goes out from lack of fuel.]]
* 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.]]
* ImposterForgotOneDetail: Max Cash tells a story of a time in his youth when a changeling impersonated one of his friends. He fooled everybody except him. This was because Max had personally murdered the friend via drowning a short time ago. Max then killed the changeling the same way.
* 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.
* InstantExpert: Rainbow Dash [[spoiler: and later Applejack and Rarity]] learns the modern language well enough to passably speak it in a matter of weeks. [[spoiler: It's hinted that something strange might be going with them to let them do that]].
* InterplayOfSexAndViolence: Charisma is sometimes turned on by the idea of others being injured.
* InUniverseNickname: Blaze for Trail Blazer.
* IWantGrandKids: The main reason the king [[spoiler: sets up Star's marriage to Regal is the hope that they'll produce an Alicorn grandchild]]. Even though it really shouldn't work [[spoiler: he seems to have had some of his family's mystic visions that suggest she'll be somehow involved in the process of their return]].
* 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 weaponized.
* 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]].
* NoIndoorVoice: Nightmare Umbra uses the Royal Canterlot Voice at all times.
* NotQuiteFlight: Bigwig can levitate platforms to carry himself at speeds rivaling pegasi (though with worse maneuvrability).
* OrwellianEditor: Someone went to great lengths to remove any mention of the Elements of Harmony from the world. Even Twilight Sparkle's book on the subject isn't mentioned in any way even though she's basically the founding figure of modern magical studies. Similarly, no one seems to have ever heard of Discord before.
* 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 shifting, breaking, tearing, and healing as she grows wings and more than doubles in size.]]
* ThePowerOfFriendship: As one might expect for a WesternAnimation/MyLittlePonyFriendshipIsMagic fic, this turns up. But things are more complicated than you would normally expect from the trope.
* ProudWarriorRace: The Griffins
* 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.]]
** The king of the Solar Kingdom genuinely wants what's best for his kingdom and people, doesn't really subscribe to the unicorn-supremacist philosophy that some of his nobles do, understands that he has limits on his power and tries to instill the same virtues on his son. His only flaw is that he [[spoiler: also wants Star to give him an alicorn grandchild to help repair the world's political divides even though it's been made clear she can't]].
* TheReasonYouSuckSpeech: Nightmare Umbra delivers a scathing one to the Solar Kingdom nobility.
-->'''Nightmare Umbra''': '''Silence'''. To Call Yourselves Noble Is Laughable. You Claim To Worship Celestia, Yet When I Look Into Your Precious, Little, Sun-Loving Faces, I Do Not See Ponies She Would Be Proud Of. Just Look At You Now: You Trample Those Weaker Underhoof In The Hope Of Buying Yourself Another Breath Of Life. Craven Beasts, That Hope Is As Empty As Your Hearts.
* RedBaron: Charisma is called "The Asskicker" by her enemies. Also, "The Killer".
* RemovingTheHeadOrDestroyingTheBrain: Nightmare Umbra's undead minions can only be destroyed by crushing their skulls. They regenerate from anything else, including decapitation.
* {{Retcon}}: In her notes, Twilight Sparkle [[spoiler: suggests that the Elements of Harmony are capable of doing this to people and fears that they may have already done so without anyone realizing it]].
* RetiredBadass: Bigwig is former military 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: ''Harmony Theory'' itself and ''The Magic of Friendship''. Both are books written by Twilight.
* SlaveRace: Every griffon is pledged to serve the Solar King, as his magic is keeping their species from extinction.
* TheSlowPath: [[spoiler:Spike made it to the future the old fashioned way.]]
* SquareCubeLaw: Due to the reduced amount of ambient magic to [[RequiredSecondaryPowers support their bodies]], dragons have to maintain a reasonable size to survive. Max Cash goads a young and inexperienced dragon named Boomer into giving into greed. This causes him to grow gigantic and powerful, but then his body starts to collapse on itself.
* 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.
** Nightmare Umbra has incredible strength and speed, but is a poor flyer, allowing Rainbow to out maneuver her. She also has terrible aim. Still, trying to fight her is nigh impossible since her stamina is unlimited, she can't be hurt permanently, and she can rip out mountain sized chunks of earth and throw them at Mach speeds.
* WalkingArmory: How Bigwig chooses to confront Charisma.
* WarGod: Nightmare Umbra is thought of this way. But she is feared rather than worshiped.
* WeHaveBecomeComplacent: Nightmare Umbra accuses the Solar Kingdom of this.
-->'''Nightmare Umbra''': Eight Hundred Years Have I Waited, Marshalling My Power. Eight Hundred Years Have I Given You To Do The Same. When I Emerged From My Silence I Expected To See Armies Arrayed Against Me! Heroes And Sages Aiding Great Leaders In Battle Against The Only Foe That Will Ever Matter For You. A Worthy Challenge To My Dominion. What Have I Found? The Petty Rulers Of A Broken World, Sitting In Pretty Rows Celebrating The Union Of A Blushing Filly And A Pampered Fop Who You Expect To Be Your Sovereign. Are You Such Fools That You Thought Me Gone Forever? Were You Not Informed Of My Return? Did You Not See The Signs?
* WillingChanneler: Nightmare Umbra is possessing the willing [[spoiler: Twinkle Shine]].
* WouldHurtAChild: Max Cash sets fire to a school for fun.
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