Many years after sending her beloved protege to Ponyville, unease sits heavily on the heart of Equestria's Sun Princess, as her relationship with Twilight Sparkle seems to have cooled despite all they've accomplished together. On the advice of her sister, Celestia sets out to investigate and resolve the lost connection with her most faithful student.

A FanFic for ''WesternAnimation/MyLittlePonyFriendshipIsMagic'' by [[http://www.fimfiction.net/user/device+heretic [=device heretic=]]], ''[[http://www.fimfiction.net/story/5921/Eternal Eternal]]''explores the bond between the Sun Princess and her Faithful Student... as well as what, exactly, both those titles truly ''mean''.

One of the fandom's two premiere Twilight/Celestia fanfics, Eternal explores a darker take on their relationship. The other, {{Fanfic/Composure}}, is a LighterAndSofter story that explores similar themes but comes to very different conclusions.

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!!''Eternal'' contains examples of the following tropes:

* [[AnthropomorphicPersonification Anthropomorphic Ponification]]: The Sun takes on the form of [[spoiler:a radiantly cruel Celestia]].
** On top of this, [[spoiler:Celestia is 'the part of The Sun that's a pony', while The Sun is the part of Celestia that is the sun]].
* ArcWords: "Eternal Sun" is more than just one of Celestia's titles.
* AnchoredShip: Twilight and Celestia can't express their feelings.
* BreakTheCutie: The war with Discord left serious psychological scars on Celestia. [[spoiler:The Sun was also innocent, naive and trusting until Celestia ''snapped''.]]
* BrokenAce: Twilight is striving to become a Type 2. [[spoiler:Celestia already is.]]
* BrokenPedestal: Celestia fears becoming this in Twilight's eyes; Princess Luna also fears breaking hers even further by revealing more of her past to Twilight and her friends.
* DeadpanSnarker: This is how Twilight and Luna's brand of playful banter is best described, which does show itself sometimes, although the latter also revels in being sly and mysterious. [[spoiler: The Sun]] gleefully and cruelly indulges in this to harass [[spoiler: Celestia.]]
* DreamWeaver: Luna has this ability to some extent, as dreams are one of her domains.
* DrivingQuestion: What does it mean to be the "Faithful Student"?
* [[spoiler: EarnYourHappyEnding: The ending is very upbeat, especially for Celestia, Twilight and Luna, but it took a lot of hardship to get there.]]
* GreenEyedMonster: [[spoiler:Princess Luna]] eventually admits they allowed the situation to deteriorate out of jealousy over [[spoiler:Celestia and Twilight's formerly close relationship]].
** Twisted around with the minor plotline of [[spoiler:Dash and Scoots' fighting]]: a large part of the problem is that [[spoiler:Dash secretly resents Scootaloo for becoming a better Captain than she was, when joining the Wonderbolts was always ''her'' dream]].
* TheGuardsMustBeCrazy: [[spoiler:Averted when Twilight's friends first try to disobey Luna's orders and get past the guards.]]
* IDidWhatIHadToDo: Celestia's justification for [[spoiler:chaining The Sun]].
* IHatePastMe: While viewing a vision of the past, [[spoiler:The Sun Itself]] is visibly irritated by seeing their past self being friendly with [[spoiler:Celestia]].
* IKnowYourTrueName: Twilight figures out the true identity of [[spoiler:Nightmare Celestia]], giving her insight on how to defeat them. [[spoiler:It's Guilt.]]
** Also important elsewhere in the dreams, especially when [[spoiler:Nightmare MOON]] ends up coming in. [[spoiler:Her true name is ''Sister''.]] Or when dealing with ''herself'' and her own identity.
* {{Irony}}: Celestia sent Twilight to learn about and report on [[ThePowerOfFriendship the nature of Friendship]], yet both struggle to put those lessons into practice with each other.
** The Sun points out another major Situational Irony: [[spoiler:as the part of The Sun that is a pony, Celestia was always meant to ''live like one'', experiencing all the world had to offer in ways The Sun could not. Instead, she became so obsessed with being the perfect Eternal Sun Princess that she grew distant and detached, the exact opposite of what she was ''meant'' and '''''wanted''''' to do]].
* JourneyToTheCenterOfTheMind: Used to get to the heart of Celestia's problems.
* LastEpisodeNewCharacter: [[spoiler:Radiant Dawn]]
* MagicalUnderpinningsOfReality: The ramifications of Celestia's role as the Sun Princess are explored.
* [[TheWomanWearingTheQueenlyMask The Mare Wearing the Sun Princess' Mask]]
** BecomingTheMask as history unfolds. Breaking past the masks is an important theme.
* MartyrWithoutACause:
-->'''Luna:''' You're just like her. You've both turned self-sacrifice into a vanity.
* NotSoDifferent: Twilight and Celestia.
* OfficialCouple: Fluttershy and Big Macintosh.
* ThePerfectionist: Twilight, much to Celestia's alarm. [[spoiler:Celestia as well.]]
* PlotParallel: Rainbow Dash and Scootaloo are having serious issues with one another due to [[spoiler:Scootaloo becoming the Wonderbolt's captain after Dash's early retirement]]. Eventually, Twilight comes to realize how this mirrors her own problems with Celestia.
* PoorCommunicationKills: The tragedy of miscommunication is a recurring theme.
* ThePunishment: [[spoiler:The Sun ultimately forces Celestia to cycle between being Princess of the Sun and living a normal, mortal life. Celestia isn't quite sure if this falls under an {{Unishment}} or not.]]
* RidiculouslySuccessfulFutureSelf: Since ''Eternal'' is set several years after the original series, a few of the Mane Cast have hit this.
* SecretTest: Played heartbreakingly early on, when Celestia realizes Twilight sees [[spoiler:her friend's wedding]] as one of these and is desperately trying to impress her by ensuring everything's '''''perfect'''''.
* ShipTease: A running theme early on is Celestia's growing confusion about ''what'', exactly, Twilight means to her, and vice versa. [[spoiler:Rainbow Dash and Spitfire]] get plenty of their own teasing later on.
** [[spoiler: Subtly, there's ''still'' a bit of this going on even after the story ends. Twilight and Celestia undoubtedly share the deepest bonds of love, but the clearest statement we get is that of dearest friends: "one soul, two bodies." There's certainly at least a degree of romantic love there, but we aren't actually told if that ever got anywhere in the end, although Celestia does state she will be "forever Twilight's" in the closing of her final letter to her in the Epilogue.]]
* [[ThisIsSomethingHesGotToDoHimself This Is Something She's Got To Do Herself]]: Though fully aware of how ThePowerOfFriendship has seen her through in the past, Twilight repeatedly wavers at the thought of getting the others involved, and eventually resolves to do this. Both Luna and Spike argue the point using this reasoning.
* TragicDream: Twilight expresses her unfulfilled desires for Celestia by sinking into dreams.
* TragicMistake: As Twilight eventually discovers, Celestia's tragic mistake was [[spoiler:binding The Sun to avoid setting, and convincing herself the ends justified the means]].
* UsedToBeASweetKid: [[spoiler: The Sun, if she could have been considered a kid when she met Celestia.]]
* WantingIsBetterThanHaving: While [[RidiculouslySuccessfulFutureSelf all of the Bearers achieved their dreams]], one of them explicitly discovered this: [[spoiler:Rainbow Dash found leading the Wonderbolts was too restrictive and demanding for her tastes, and wound up leaving the position]].
* WasItReallyWorthIt: Celestia asked herself this after banishing Luna.
* WeUsedToBeFriends: [[spoiler:Celestia used to be close to The Sun, before her betrayal.]]
* WeddingDay: Fluttershy and Big Macintosh are getting married, giving Celestia an excuse to visit and see precisely how Twilight is doing.
* WhatTheHellHero: Somepony has to answer to this.
* AWizardDidIt: A RunningGag is Twilight's increasing frustration whenever she's informed that something has a mystical origin too complicated to explain concisely.
* YouDontWantToKnow: [[spoiler: When Celestia tell Twilight Sparkle that she is the part of the Sun that is a pony and the Sun is the part of her that is the sun, Celestia immediately says that she won't explain it as the answer is something Twilight won't like. Twilight Sparkle, however, merely wanted to know if Luna had a similar arrangement.]]
* YourMindMakesItReal: While dreaming, they still can still experience severe pain. [[spoiler: Luna attacked by Twilight's mental defenses. Twilight bound by gold chains.]] It also works outside the dream. [[spoiler:Luna ends up scared when, after smashing through a glass table in her dream, Twilight's real body has slashes across it.]]