She is beautiful. She is sweet. She is sincere. So why can't she get the guy already? The Unrequited Tragic Maiden is (usually) a female character that seems to have all the perfect characteristics to make her the ideal romantic interest or even The Ingenue of the story, but alas, for some reason the object of her affections does not view her as such. Usually this is because she is overshadowed by another female character who has captivated the heart of the guy, placing the Unrequited Tragic Maiden on the sideline only to be seen as a friend or ward.
No matter how painful her yearning for love is, the Unrequited Tragic Maiden never truly achieves her happily ever after with the one she loves. She endures it all with a sad smile and is often reduced to a tragic fate. She is the poster child of Unrequited Love. In the end she will often sacrifice herself or her happiness to make sure her beloved is happy.
Fan reactions to her tend to be mixed. Many fans will cheer and push for the Maiden's success, to the extent of calling The Hero an Ungrateful Bastard if he doesn't fall to the girl's feet (because the often never asked for pining and sacrifices are seen by fans as him owing her affection or sex no matter what he actually thinks or says) or Slut Shaming any possible female love rival (because The Hero is seen as a tool of women's validation and some think that women shouldn't act on their own romantic feelings if it interferes with others); and if the Maiden doesn't succeed, much bashing of the author shall be expected. On the other hand, others will turn against the Maiden and call her insulting names; this is especially obvious if either The Hero has another prospect love interest or female friend who's perceived as being "stronger" and "cooler" than the maiden herself, or the Maiden herself has a prospect male love interest whose (canon or not) feelings she passes up on to favor The Hero.
Compare to Hopeless Suitor and Romantic Runner Up, who is the brother of this trope but usually with a less tragic end. May wind up becoming The Lost Lenore after death if the person they loved grieves for them, blames themselves for her death or else only discovers that he loved her until it is too late. Contrast to Green-Eyed Monster, in which is more prone to sabotoge and a devious nature unlike the docile nature of the Unrequited Tragic Maiden.
This is starting to become either a Discredited Trope as romantic portrayals of females become less dependent on the male characters, or a Deconstructed Trope to showcase a point-of-view of it being an unrealistic idea of romantic love.
Examples:
Anime and Manga
Actually negated in regards to Ahiru from Princess Tutu, both by Word Of God saying that Ahiru's feelings for Mytho were less romantic and more like strong platonic admiration, and by how after Rue's Heroic Sacrifice, Ahiru confides in Fakir that she would've never been able to sacrifice her human form solely for Mytho's sake. Since Tutu's magical pendant has one of Mytho's heart shards and Ahiru depends on it since she's a duck given a human form through said pendant (not a girl who turns into duck, as fanon says), deep down Ahiru very understandably doesn't want to part from it, and she says she would've thought twice upon having to give it away - unlike Rue, who upon being on the verge of losing her beloved Mytho forever, immediately told the Raven King to eat her heart instead, which liberated Mytho from the Raven's control. In a sense, we could say that Rue, despite being an Anti-VillainDark Magical Girl, has more than one whiff of the trope, and only barely avoided either losing or dying.
It could be said that Tutu filled the role in the backstory of the series. But one of the biggest points of Princess Tutu is to have the characters fight against the rules that Drosselmeyer, as the writer of the story, wants to impose on them. This certainly includes Ahiru: as a cute duck given a human form so she would become Tutu and fill this Unrequited Tragic Maiden spot, she ultimately decides to go beyond it whether as a human or as a duck. She basically said "FUCK YOU" to the trope.
Sayaka Miki in Puella Magi Madoka Magica. She yearns for Kyousuke's love, but he shows no romantic interest in her and after Sayaka doesn't confess her love for him in time, he hooks up with Hitomi, who did come forward when she had the chance. Things do NOT end well for Sayaka.
While Sayaka has quite a bit of this trope, viewing her as such more often than not flattens her personality and in-canon conflicts. The truth is far more complex: Sayaka already had had serious self-esteem problems before becoming a Magical Girl, and when she's offered to become one and mentions that she wanted to use her wish for Kyousuke's sake, Cool Big Sis Mami immediately questions her purpose. She makes her wish for him against Mami's warnings, since she sincerely believes it would still be worth it; only then Sayaka learns that being a Magical Girlis NOT as sparkly and beautiful as she thought it was, clashing with her black and white view of the world as well as her emotional conflicts; while losing in the Love Triangle is a part of the reason why she fellout of grace , is not the only reason. But go tell that to several of her "fans", who peg the girl only as the local Unrequited Tragic Maiden and then make her a Possession Sue... when actually, she can be seen as a deconstruction of the trope, since the UTM concept relays on a painfully unrealistic view of romantic love and Sayaka's plot is a proof of it.
Shirley Fenette from Code Geass. And right when it looks like she may have had the chance to get Lelouch's love... BAM! Bullet to the gut, pool of her own blood, death in front of Lelouch.
Played with in Ano Hana The Flower We Saw That Day. Menma suffers a tragic death right after hearing Jintan deny having a crush on her. In reality, he returned her feelings while she was alive, and still liked her even when she was a ghost.
Kaede Fuyou from the SHUFFLE! TV series is a rather unusual example, as she plays this straight first... and then dips into yandere. Though she gets better, and she has rather screwed up reasons for her Yandere episode. In the original Visual Novel, whether Kaede is this or not... it actually depends on the player.
There's one in Ten Yori Mo Hoshi Yori Mo. It's not Mio Mizumori, who actually has her feelings for Shou requited very soon. It's actually Miyabi Fujiwara, the local Ojou, who falls for Shou at first, then is manipulated by Tadaomi due to her feelings... and ends up dying in a plane crash caused by Tadaomi in an attempto to kill Shou.
Shirley Marks from Captain Tsubasa, to a degree. She loves Stefan Levin deeply, can't tell him her feelings because his dead fiancée Karen was her best friend and she clearly knows he simply can't love her back. This is a pretty sucky situation, but the girl is somewhat genre savvier than usual and she attempts to not wangst and complain about it.
Openly defied in InuYasha. The Baby deals several and extremely cruel Breaking Lectures to Kagome, telling her that she's pretty much condemned to be this to Inuyasha himself, due to his feelings for his ex-girlfriend (and Kagome's past self) Kikyou. Kagome is this close to give into them and have a Face Heel Turn, which is the Baby's purpose... but then she snaps back at him, aknowledging that yes, she is often jealous of Kikyou, but that these feels are proper of human beings and that she does love Inuyasha anyway. Such emotional honesty, and specially coming from a Tsundere and self-admitted Clingy Jealous Girl, is VERY welcome and refreshing. And even more so when it keeps her from going the "Love Makes You Evil" way.
In the anime, Princess Sara plays it straighter. Her deal is muchmorecomplex, though.
Played with in Daily Life With Monster Girl, with Mero. She wants to be the Unrequited Tragic Maiden to the man she harbors affection for, eagerly stepping on the sidelines and only wanting to be a tangential part of the protagonist's harem.
In the Marmalade Boy anime Anju Kitahara has more than one whiff of this, being a Yamato Nadeshiko and loving her Childhood Friend Yuu, who already has a girlfriend named Miki by the time they meet again... but she immediately recognizes the trope and tells Miki that not only she will not step in between them but she'll support them as much as she can. She does have a slim chance later when Yuu and Miki break up during a crisis, but since they hook up again later, Anju decides to step aside.
Tomoyo Daidouji from Card Captor Sakurais viewed by the CCS fandom as a Les Yay version of this trope, due to her romantic feelings for Sakura Kinomoto. (Straight-up confirmed in the manga!) In reality Tomoyo could have been one, but ultimately she was NOT: she neither hopelessly waited for Sakura to notice her, nor expected to have her feelings reciprocated after helping her with her mission. Instead she wholeheartily supported Li Syaoran's affections for Sakura as soon as she spotted them.
Literature
In the original story of Hans Christian Andersen's fairy tale, "The Little Mermaid", the mermaid rescues and falls in love with a prince. He marries a different girl whom he believes had rescued him, and who actually did help in his rescue (and in some versions she was actually his bethrothed from before the mermaid incident happened). Because she was unsuccesful in making the prince fall in love with her, the mermaid turns to sea foam, choosing his happiness over her own life. In some versions she is rewarded for her sacrifice with a new life as an air sprite, during which time she will earn a soul (mermaids don't naturally have them) and go to Heaven.
The Lady Of Shalott (the page image) from Alfred Lord Tennyson's poem of the same name which is based on the Arthurian Legend character Elaine of Astolat, who pined after Lancelot (who, of course, only had eyes for Guenivere) and eventually died of a broken heart.
Rebecca of York to Ivanhoe, due entirely to the fact that she's Jewish. She warns Ivanhoe not to fall for her at their first meeting and does a graceful I Want My Beloved to Be Happy bow out at the end allowing Rowena and Ivanhoe to be together and devotes the rest of her life to doing good works. Notable in that even the authorpreferred Rebecca and Ivanhoe.
Live Action Television
In Smallville, Chloe is solidly pining after Clark for the first five seasons, and even after getting together with Jimmy for season six and seven, it is pretty obvious that she would be with Clark if she gets to choose. Not to mention an Anguished Declaration of Love in late season seven. Subverted when she seems to be Happily Married with Jimmy. Double subverted when Jimmy divorced her for always taking Clark's or Davis' side. Triple subverted when she ends up with Oliver. Although that probably counts as being Strangled by the Red String.
Willow on Buffy the Vampire Slayer was this for a while, pining away for Xander, until she got a boyfriend of her own. And then became (or realized she was) a lesbian or a lesbian-leaning bi.
Theater
Giselle from the ballet of the same name. In some versions, Giselle falls in love with Albretch, but Albretch is engaged to Bathilde. After dying of a broken heart, Giselle becomes The Lost Lenore.
Ophelia from Hamlet might be seen as one. Against the warning of her father, she's fallen in love with the Prince, and as soon as Hamlet begins to feign madness, the first thing he does is try to break off his relationship with Ophelia. She doesn't take it well. At her funeral, Hamlet sobs profusely for his love for her.
Eponine from Les Misérables is in love with Marius and does everything she can to help him, even though he is in love with Cosette and only views Eponine as a friend.
Helen Chao from "Flower Drum Song" is one of these. Like Eponine, she gets one of the arguably better songs in the show and does everything she can to be a supportive friend to Ta. He first rejects her by chasing the wrong love object before again passing her over for the intended love interest.
Video Games
Namine from Kingdom Hearts is drawn to Sora and wishes she were Kairi. In the end, she wants Sora and Kairi to be happy and merges with Kairi thus destroying her own identity and existence in some ways.
Path of Radiance has Titania, second-in-command and Team Mom of the Greil Mercenaries. It's revealed in her Supports with Ike that she grew close to and became enamored with Ike's father Greil while training under him, but she pushed away her feelings for Greil when she discovered that he was already married with children. It should be no surprise that she (along with Ike and Mist) is hit the hardest by his death at the hands of the Black Knight (to the point that she breaks down into tears in their A Support when Ike thanks her for taking care of his father in his final years). She does have Ship Tease with Ike, Boyd, and Rhys in Radiance, but ultimately ends up single by the end of Dawn.
Blazing Sword has a Double Subversion in Priscilla. She does have a number of possible lovers she can Support with, but due to her status as nobility, she ultimately ends up in a Star-Crossed Lovers situation — with all but one of them the magician Erk, who has peerage only due to his tutelage under Pent, the Count of Reglay.
Also, if Eliwood reaches an A support with anyone but Ninian, she will become this since her romantic feelings for Eliwood are set in stone regardless of support levels.
Cordelia/Tiamo in Fire Emblem: Awakening is in love with Chrom and is hurting badly over it, but will never say anything because she's sure it'll never work out. The game mechanics don't even let you pair them!
Julia from Geneaology of the Holy War predates them all. She falls in love with her half-brother Seliph, but cannot pair with him... without glitches. (And it's even lampshaded in-game, with Seliph's potential love interest Lana actually feeling guilty upon having her feelings requited.) Averted in the Oosawa manga, where the ending strongly hints at them ending up together even after finding out that they're half-siblings.
Sylvia also is this in the Oosawa manga. She fell in love with Lewyn after he showed her the kindness nobody else would and proclaims her feelings for him more than once. However, Lewyn also has feelings for Ferry, whom he professes his love to during the Silesia arc, after apologizing to Sylvia due to being unable to like her back.
