Sometime in the [[TwentyMinutesIntoTheFuture super-present]], the fabled and mysterious Tomb of Gilgamesh is discovered by scientists who are digging around in Uruk (modern day Mesopotamia). A research center is promptly set up to study the strange energy which is being emitted by the site, but a series of events triggered by the site's discoverer, Terumichi Madoka, soon result in a global catastrophe which knocks out all electronics worldwide and turns the sky into a giant electromagnetic mirror. Terumichi (who now calls himself Enkidu, after a character in the ancient ''[[Literature/TheEpicOfGilgamesh Epic of Gilgamesh]]''), is labelled a terrorist and promptly vanishes.

Fifteen years later, his two hapless children, Tatsuya and Kiyoko, are in Japan being chased down a city street by some thugs who want to shake them down for some debts owed by their late mother. The children duck into a creepy old mansion, where they run into some gothy teenagers who seem strangely knowledgeable about their situation. The goth-teens, who call themselves the Gilgamesh, rescue the children from the thugs using mysterious [[PsychicPowers psycho-kinetic powers]], and then invite the siblings to join their side in a war which will [[TheEndofTheWorldAsWeKnowIt cleanse the Earth]] and make way for [[EvolutionaryLevels the next evolutionary stage of humanity]].

Before Tatsuya and Kiyoko can even give the matter a nanosecond's worth of thought, another group of super-powered children drop by and attempt to get the siblings to join ''their'' group, the ORGA, which is opposed to the goth-teens and their fanatical leader -- who just happens to be the sibling's [[LukeIAmYourFather long-lost father]]. The ORGA are led by [[EvilMatriarch Kageyama Hiroko]], the [[AristocratsAreEvil Countess Von Werdenburg]], an enigmatic, elegant black widow who was once a research colleague of Terumichi Madoka, and who is now his bitterest enemy. She claims that her true goal is to save humanity, but is she really all that trustworthy? (And was she really "just a colleague" of their father's? Or something ''more''?)

''Gilgamesh'' is a tale packed with intrigue. Not only does it feature the above characters, there's also a [[CorruptCorporateExecutive corrupt corporation]], with a vicious PsychoForHire, Kazamatsuri Hayato, at its beck and call, and a group of well-intentioned (but ultimately ineffectual) scientists who are trying their best to get the Earth back to normal. Throw some clones, some tragic backstory and some Ancient Sumerian Mythology into the mix, and you have a series that makes for some pretty compelling watching.

One thing to note before you dive in, however; this series is ''dark''. ''Very'' dark. ''Crows sipping coffee from an iron kettle while sitting at the bottom of a mine shaft in the middle of a moonless winter night'' dark. The art design is ugly and minimalist at times, which a cynical viewer might blame on a shrinking animation budget, but which also fits very well with the depressing and apathetic tone of the series. There are no true good guys here. The children at the center of the story never really ''know'' who they can trust, and they soon find the ambiguity of their situation every bit as dangerous an enemy as any physical monster they may face. That fact -- along with its complexity, apocalyptic themes and flawed characters -- makes it a very atypical series.

Although it does bear something of a passing resemblance to ''Anime/NeonGenesisEvangelion'', which it may have been influenced by, the manga this series is based on dates from 1972.

For the original Sumerian story, see ''Literature/TheEpicOfGilgamesh''. No relation to [[MemeticMutation GIRUGAMESH!]]. For the mightiest swordsman in all Ivalice, click [[VideoGame/FinalFantasyXII here]], or you may find him [[VideoGame/FinalFantasyV here]]. For the Argentine comic book, see [[ComicBook/GilgameshTheImmortal here]].

!!This show provides examples of:

* AdaptationDistillation: A lot was changed from Creator/ShotaroIshinomori's original 1972 work. Most noticeably, the removal of extraterrestrials. The anime does share common themes with the original, though. The brother-sister pair Tatsuya and Kiyoko, along with an onyomi Enkidu name show up in both, although the kanji for the latter differs from the original. May also be a PragmaticAdaptation.
* AfterTheEnd: An important scene after the ending credits takes place here.
* AllergicToLove: Fuko, a bit literally, with her sneezing.
* AndIMustScream: Literally, Kiyoko does, while trapped in [[spoiler: genetic matter]].
--> "Ta... tsu... ya..."
* AristocratsAreEvil: The Countess, while not outwardly ''evil'', really isn't all that nice a lady.
** The old man's son qualifies... [[spoiler: "tell them a girl in a kimono set fire to it, and ran off"]]
* BackFromTheDead: The super-powered followers of Terumichi Madoka (Enkidu) apparently all have the ability to do this, although it doesn't stop them from being KilledOffForReal if the plot demands it.
* BizarreBabyBoom: The super-powered teens were all created from embryos exposed to AppliedPhlebotinum.
* BodyHorror: Occurs when [[spoiler:Kiyoko gets pregnant]].
* BrotherSisterIncest: Tatsuya and Kiyoko only had each other to depend on, since their mother was a neglectful alcoholic. Still, their relationship seems a bit... ''closer'' than what might be construed as normal.
** Add to the bag that Tatsuya is [[spoiler:not only her brother, but also the clone of their father]].
* CloningBlues: [[spoiler:Tatsuya and the three ORGA. And to an extent, Yuki.]]
* CrapsackWorld
* CoitusUninterruptus
* CrystalDragonJesus: Instead of raiding Christianity for symbolism, this series incorporates lots of ancient Sumerian religious mythology.
* DespairEventHorizon: You hit this at about the half-way mark and it all goes downhill from there.
* DownerEnding: [[spoiler: And beginning. And middle. It's kind of a relief to see them all put out of their misery at the end.]]
* DyingDeclarationOfLove: At the end, Novem [[spoiler: confesses to Tatsuya that he loved Kiyoko.]] In fact, [[spoiler: Novem and Kiyoko's entire relationship may fall under the StarCrossedLovers, divide considering that they were from two different species who, at the point when their relationship manifests, were supposed to be fighting each other in a desperate attempt to bring about a future for the human race. How things eventually ended is ''certainly'' tragic enough to qualify. In any case, the other Gilgamesh are ''really'' not happy when they find out Novem's been sleeping with their boss's daughter.]]
* TheEndOfTheWorldAsWeKnowIt
* EverybodyKnewAlready: When the truth of Reiko is spelled out [[spoiler: that "she" is technically a boy]], everyone but Tohru (and perhaps the audience) already knew, and acts like "What? You just figured out?"
* EvilMatriarch: Kageyama Hiroko. Although apparently we are supposed to sympathize with her because of her sad past.
* GainaxEnding
* GoMadFromTheRevelation: What ever [[spoiler: Tear tells Kiyoko]] at the end of the series ([[TheseAreThingsManWasNotMeantToKnow that the audience]] [[TheUnreveal doesn't get to hear]]) seems to immediately destroy her sanity, causing her to stab the former to death. Cue SlasherSmile.
* GreyAndGrayMorality: You'll need the higgs boson and a very sophisticated calculator to figure out where to draw any morality lines. Have fun with that.
* HalfHumanHybrid
* HeadbuttOfLove: This is not just a means of giving comfort to a character, but a way the ORGA teens can exchange energy as well.
* IdenticalGrandson[=/=]GenerationXerox: this is an interesting case, because both the ORGA and Tatsuya [[spoiler: are clones of their "parents"]], however Kiyoko looks exactly like her mother, and when there is a flashback to when Kiyoko and Tatsuya's mother and father met, the exact replication [[IncestIsRelative has certain]] [[BrotherSisterIncest incestuous connotations]].
* InterspeciesRomance: [[spoiler: Kiyoko and Novem. Their relationship results in Kiyoko's pregnancy.]]
* KickTheDog: The corporate PsychoForHire engages in this a LOT.
* KillEmAll
* NoseBleed: Tatsuya gets one (but not the explosive kind) when one of the ORGA teens, Fuko, lends him some of her psychic energy through a HeadbuttOfLove mentioned above. The implications of the nose bleed are made clearer when Fuko cracks that [[DoubleEntendre she bled a little her first time, too]].
* OppositeSexClone: [[spoiler: Reiko Yuki is technically a boy as she is a clone of Chairman Toranosuke Yuki of The Mitleid Corporation.]]
* ParentalAbandonment: Kiyoko and Tatsuya.
* PsychicPowers: Dynamis.
* PsychoForHire: Kazamatsuri Hayato.
* PsychoticSmirk / SlasherSmile. [[spoiler: Kiyoko]] gives one after [[spoiler: stabbing Tear to death with the tuning fork at the end.]]
* ScaryShinyGlasses
* ShootTheShaggyDog: One of the most spiteful ever. Kiyoko, having already lost everyone and everything she cared about, having been forced into debt, despair, and work as a call-girl by the very Countess supposedly trying to "save the world" whilst ruining the lives around her, and who in lonely desperation turned to a member of the opposing Gilgamesh who then impregnated her, dies after mutating into a birthing cocoon for the hybrid lifeform. In the climactic final battles against the twisted Enkidu, his cohorts, and the Gilgamesh forces, it's revealed that they're essentially unstoppable and un-killable. This leads to the Kill 'em All deaths of pretty much everyone in the cast not already dead at this point. In the end, it's revealed that the TeaR organism responsible for the first near-apocalypse and which has instigated the horrible events of the story is actually a living manifestation of the Countess's own petty, dark, hateful, jealous, twisted heart, and that she's directly responsible for everything without realising it, despite ostensibly and ironically trying to fix it. Upon this revelation, she accepts the death of Humanity and allows TeaR to wipe out all life on Earth. To add insult to injury, in the odd, meta-void left behind, TeaR is then killed by the Gilgamesh spawn from the husk of what was left of Kiyoko, meaning that TeaR won't go on to recreate the planet in its image and it's all gone for good.
* SmugSnake: Kazamatsuri Hayato.
* SnowMeansLove: In a dream flashback which explores the relationship between the two main siblings.
* SoundtrackDissonance: The opening theme is a peppy, upbeat electronic pop song that doesn't match the series at all.
* SuperSoldier
* TeleportersAndTransporters: Besides {{telepathy}} and {{telekinesis}}, one of the superpowers held by the ORGA teenagers and the Gilgamesh.
* TheUnreveal: [[spoiler: Tear]] tells [[spoiler: Kiyoko]] something at the very end. The audience never hears what was said... but whatever it was, the latter [[GoMadFromTheRevelation does]] ''[[GoMadFromTheRevelation not]]'' [[GoMadFromTheRevelation take it well.]]
* TragicHero
* TwistEnding
* UnsettlingGenderReveal: Reiko. It certainly unsettled poor Tohru, who had been developing feelings for "her."
* WellIntentionedExtremist: Enkidu and, at times, the Countess.
* WhatHaveIDone: [[spoiler: Hiroko Kageyama. But she gets over it pretty quickly.]]
* WholesomeCrossdresser: [[spoiler:Reiko, who was apparently encouraged to cross-dress in order to make him more docile and agreeable.]]

->''[[RunningGag GUHROOGAMASH!!!]]''