''Yami to Boushi to Hon no Tabibito'' (Yami, the Hat, and the Book Travellers), a.k.a. ''Yamibou''

The Great Library: [[MagicalLibrary A place where every world is maintained within books]]. By and large, people can live out their entire lives without ever knowing it exists.

Azuma Hazuki was living out her life as a fairly OrdinaryHighSchoolStudent in one of these worlds, until her adopted sister, Hatsumi, disappeared at midnight on her [[DangerousSixteenthBirthday sixteenth birthday]]. Intruding immediately on her shock was a bird-like being called Ken-chan, which had been sent by its master to find someone called Eve...

''Yamibou'' is, simply, the story of the people whose lives were touched by Eve as she travelled through the worlds contained in the books of the Great Library, and their continued attempts to find her. From Lilith, the current guardian of the Great Library and caretaker of its books (that's supposed to be Eve's job); to Gargantua, whose life was forever altered when he witnessed Eve's apparently magical powers during her stay in his world; and finally to Hazuki, who loves her adopted sister and sought to find her at any cost; each had their own reasons to search.

Many have called ''Yamibou'' a watershed moment for serious [[SchoolgirlLesbians schoolgirl lesbian]] moments in anime (though it's been played as comedy since at least 1999 in ''SteelAngelKurumi'', and probably earlier), the recent rise of ''yuri'' in anime can easily trace its beginning to the late-2003 run of this show. Humorously enough, many of the people who watched the show for just that reason, and who had glowingly referred to it as the defining ''shoujo-ai'' series, absolutely despised the ending. (Several have since attempted to pass the mantle of "defining ''yuri'' series" to ''KannazukiNoMiko''.)

''Yamibou'' is based on an [[DatingSim "H"-game]] by Root with artwork done by Carnelian. The original game's plot is vastly different, lacking much of the ''yuri'' due to starring a nameless male main character (who was completely eliminated from the anime.)
This show provides examples of:
* AirplaneOfLove
* AllJustADream: Hazuki and Hatsumi share a very passionate scene, only to have it turn out to be nothing more than a dream--in the new world at least.
* AloofDarkHairedGirl: Hazuki has long dark blue hair and shows very little emotion to everyone but Hatsumi.
* AlternateContinuity: The series itself, compared to the game by Carnelian.
* AnachronicOrder: The first episode is broken into two parts, depicting the very start of Hazuki's quest and a later adventure within it.
* AncientKeeper
* BaitAndSwitchLesbians: [[spoiler:Hazuki never gets her girl, but will ''give birth to her'' as a daughter sometime in the future.]]
* BecauseDestinySaysSo: Eve's continued disappearances--though this may not be "destiny" so much as a basic part of Eve's character, which makes it all the more infuriating.
* BleachedUnderpants
* CharacterExaggeration: In the game, Lilith is an intelligent and cunning woman, if somewhat of a flirt. Only the 'flirt' part seemed to make the transition to the anime, leaving her a borderline bimbo with a lust for Hazuki that wasn't present previously--though even in the anime she hints at being more intelligent and compassionate than meets the eye now and then.
* CipherScything The nameless body-hopping protagonist of the game is replaced by the minor character Hazuki.
* CuteMute: Hatsumi. Subverted; she actually can talk at times.
* DangerousSixteenthBirthday: Azuma Hatsumi (Eve) disappears from any world she enters upon turning 16.
* [[spoiler:DidNotGetTheGirl: At least in the anime.]]
* EvenTheGirlsWantHer: Hazuki; however, [[SingleTargetSexuality if they're not Hatsumi, she's not interested]].
* FalseCameraEffects
* {{Fanservice}}: Covering pretty much every sub-category, too.
* FracturedFairyTale: One story involves a princess who must choose from a selection of princes who are, due to tradition, forced to dress up like frogs and hop around ...
* FriendToAllLivingThings: Quill.
* GainaxEnding: Fans are divided as to whether it's a DownerEnding or not.
** Only because we don't have a 'bullshit! ending' trope...
** It's actually three endings at once, none of which fit together. In one part, Hatsumi leaves a message, in the next, the message is entirely erased. Many fans nowadays seem to think the ending is supposed to be a Pick-and-Choose-your-ending thing.
* GaidenGame: ''Yamibou''s visual novel was given one in the form of ''Koge to Lilith no [[GratuitousGerman Nachtmusik]]''. It's basically Lilith having lots of encounters with people in [[{{Cosplay}} various outfits]]. FridgeBrilliance dictates that it's probably to make it easier to fit in wherever she goes...
** Bonus points for some of those outfits being [[ShoutOut call-backs]] to some of the older games that Carnelian worked on, like ''[[MoonlightLady KaoNoNaiTsuki]]'' and ''Machine Maiden''.
* HairColors
* HotLibrarian: In a more literal sense.
* ImmortalImmaturity: Lilith and Eve are rather immature despite being thousands of years old.
* ImmortalityBeginsAtTwenty: Gargantua and Ritsuko are bathed in the "Light of Eve" as young children, which causes them to stop aging once they finish growing up.
* JigsawPuzzlePlot
* {{Joshikousei}}
* KansaiRegionalAccent
* {{Kawaiiko}}: Lilith, among others.
* LikeParentLikeSpouse: The reason behind Lilith's crush on Hazuki is that she reminds her of her father, [[ParentalIncest whom she was in love with]].
* LoveLetter
* MagicalLibrary: The Great Library consists of books that contain every single world of the multiverse down to the smallest detail.
* MagicLibrarian
* MayflyDecemberRomance
* MedievalEuropeanFantasy
* MultipleTailedBeast: It stars two {{kitsune}}s, one with nine tails and one with just two.
* NiceHat: Right there in the title, and the picture.
* NubileSavage: Quill.
* ObfuscatingStupidity: Hatsumi is nowhere near as innocent or cute as she first appears.
* OrdinaryHighSchoolStudent: Azuma Hazuki.
* ParentalAbandonment: Hazuki and Hatsumi may well have parents, but they never appear, though Hazuki asks her mother a question in the final episode.
* PillarOfLight
* ReallySevenHundredYearsOld: Possibly. FridgeLogic suggests Hazuki has spent an improbable amount of time in various books, and it may be more like seven million. Of course, time itself is up for grabs in this series.
* {{Reincarnation}}
* SchoolgirlLesbians: At the time of its release, practically the Platonic ideal of Schoolgirl Lesbians. Wow.
* ShoutOut: Leading to possible EpilepticTrees: Hazuki shares her last name with Io Azuma, a protagonist of ROOT's previous visual novel (also with Carnelian's art), ''[[MoonlightLady Kao no Nai Tsuki]]''.
* SpellMyNameWithAnS: Upon broadcast, the most commonly-viewed fansubbed version of the anime had some rather different ideas on name spellings. Among them were Marieru instead of Mariel, Garuganchua instead of Gargantua, Jiru instead of Jill, and most noticeably, Ririsu instead of Lilith. (Curiously, they did not render Adam and Eve as Adamu and Ibu.) A re-release by a different group in 2007 used the romanizations listed in TheOtherWiki.
* SuperDeformed: Koge-chibi.
* ThemeTuneCameo
* TrappedInAnotherWorld: In several worlds, actually.
* UniversalAdaptorCast: The characters reenact the plots of several books.
* TwelveEpisodeAnime