Tabby from .hack//Roots isn't actually in love with Haseo, but she wants to help him in any way she can. The already Jerkass Haseo starts going to every length possible to find who or whatever caused Shino, the only one he could really open up to, to fall into a coma, but his obsession quickly causes him to lose his way. Both Shino and Haseo are Tabby's friends, and she just wants to help them both in any way she can, in the game or in the real world. Haseo thinks she's just getting in the way, but that's HIS problem. Even after telling her to never show herself ever again, she continues to help him in any way she can, just to ensure his happiness. Things work out in the end for everyone though when Haseo comes to his senses and apologizes to Tabby and thanks her for everything she's done and sticking with him through everything he put her through.
Obi from Akagami no Shirayukihime ends up falling for Shirayuki and says he "likes" Zen without further clarifying if he means romantically or not though the implication is there but remains a Shipper on Deck for their relationship even after Zen confronts him about his feelings and Obi spends two years at Shirayuki's side away from Zen when she accepts a research position in the north.
Axis Powers Hetalia has Spain letting Italy leave him during the War of the Austrian Succession. Sweden briefly thought of letting Finland go during the Polish-Swedish wars. However, he couldn't bring himself to touch the subject.
Battle Angel Alita has an odd example where a character sets her love interest up with herself. Or rather, a clone of herself, created using her original brain, which Alita does when she realizes that she may not survive the final leg of her journey and fulfill her promise to return to Figure Four.
Bi no Kyoujin has Kouki, Nirasawa's partner in crime and on-and-off best friend who is actually in love with him. But since Nirasawa doesn't reciprocate and is already spoken for, namely by a Yakuza leader who treats him fairly, Kouki accepts the situation and eventually decides to leave town so as to start anew somewhere else.
Yuzu Yamamoto in Bitter Virgin liked the main lead Daisuke Suwa. She was quick to notice that Daisuke was developing feelings for Hinako Aikawa, and after some wrestling with the issue decided to support Hinako. Up until she inadvertently learned Hinako had given birth to a child and ends up blurting this out to Daisuke. Unknown to her, Daisuke was fully aware of this already and it only cements her status as Unlucky Childhood Friend. Also, resident Yandere Kazuki also has a moment of this when she comes to the same realization as Yuzu. Though in her case she's only stepping aside temporarily as everyone is certain the relationship will ultimately fail. (Including Hinako and Daisuke, themselves.)
Elizabeth from Black Butler to the point where's she is willing to give her own life away and drown just to see Ciel smile again.
In Blood+, use of this trope could be attributed to several characters, the most notable being Mao and Haji.
When Mao believes that Kai has fallen in love with Saya, she spends the next episode making sure they get to spend some Quality Time together. This after she stole money from her yakuza boss and chased him across the globe with a complete stranger too.
Haji, meanwhile, spends the vast majority of the series doing whatever it is that will make Saya happy, and does his best to stay by the wayside (however, he also somewhat subverts the trope in later episodes, when Saya is nearly whisked off by the infatuated Solomon, and Haji makes it clear that he is not pleased).
Hilariously enough, once Saya makes it clear that she returns Haji's unspoken feelings, Solomon invokes this trope, and decides that even though they'll never be together romantically, he'll still do his damnedest to protect her so she can get the chance to be happy with Haji. Not so hilariously, this gets him killed by his former comrades, with Saya being none the wiser.
Shigeru, Sakurako, Rui, Kazuya, and Umi in Boys over Flowers give up their pursuit of Tsukushi and Domyouji so the two of them can stay together.
A Bride's Story: Talas' sixth husband, who upon realizing he's gone through an Arranged Marriage with someone in love with someone else, decides instead to help her unite with her beloved by escorting her from modern-day Turkestan into Ankara and then agrees to fake her death so she's free of her family (and he can remarry). When asked why he went to these lengths he explains that the world is a cruel place and helping others obtain their happiness is the right thing to do. It also helps that he was a widower who loved his first wife (and still does), and knows how rare and precious a thing love is and how cruel it is to take it from someone.
Cardcaptor Sakura has Tomoyo perfectly content to be just Sakuras best friend despite being in love with her. She even became a Shipper on Deck for Syaoran/Sakura.
Downplayed with Shizuku Kurogane from Chivalry of a Failed Knight, who is in love with her brother, Ikki, to the point of coming off as a Yandere at times. However, she prioritizes Ikki's happiness above her own and begrudgingly accepts that he's in love with Stella Vermillion.
In general Lelouch defaults to this. A good chunk of the Zero Requiem revolved around making sure everyone else would be happy, setting up for a world without hatred and war. Even "cursing" Suzaku to being Zero for the rest of his life was meant to give him a reason to live and hopefully move on, find his own happiness. However, the finale shows he wasn't entirely correct with what those he cares for wants. Nunnally wanted more than anything to live a normal life with her brother and ends up crying as he dies in her arms, and placed into being the Empress of Britannia. Even though she's strong enough to move on even after that, her own true happiness and dream was crushed on the way to world peace.
Milly does this as well. She has a crush on Lelouch, but her ultimate goal during Cupid's day was to pair Lelouch and Shirley. But it was probably not for Lelouch, who has no obvious love for Shirley, but rather for her friend Shirley, because she has the true big love for Lelouch, compared to Milly's crush.
In the manga Corsair, Sesaam takes in Canale who is an assassin assigned to kill him. He protects Canale and loves him dearly, and Canale eventually falls in love with him. However, Canale still feels he has no choice but to kill him, and after being stabbed Sesaam reassures Canale that he doesn't blame him, and tells him how to escape through the trapdoor under his bed, and tells him it's okay to move on after his death. 8 years later, Canale returns and finds out Sesaam survived but can no longer use his leg. He tries to seduce Canale again, but a Wrong Name Outburst leads to Canale sobbingly confessing that he found someone else. Sesaam accepts it, and says he stands by his former words. He then still tries to protect him and help him out after this.
Much of the drama in the second season of Da Capo arises from one character refusing to accept this concept. It only makes the shipping wars worse.
Danganronpa 3 has Juzo Sakakura, who is heavily implied to have feelings either for Munakata or Yukizome, later revealed to be Munakata. He realizes that both are in love with each other, and accepts to just be their friend and never let his feeling be known.
In the manga Descendants of Darkness, Tsuzuki accidentally winds up trapped in a magical self-writing romantic novel created by the pervy Count and featuring fictional counterparts of the main cast. The novel's plot mostly centers around the efforts of Tatsumi's fictional counterpart Butler to force the love of his life, Tsuzuki's gender-flipped counterpart Luka, into marriage with the rich His Lordship so that she might be financially secure. (Tsuzuki sees fit to interfere and ends up getting Butler and Luka together before he's finally rescued from the book world; Tatsumi, who is emotionally constipated to the point that Tsuzuki isn't sure Tatsumi gives a damn about him even though Tatsumi in fact cares very much, finds the whole experience very cathartic. Other onlookers among the cast, including Tsuzuki's partner Hisoka and the Count responsible for the whole mess, are mostly puzzled and amused to varying degrees.)
In D.N.Angel we have Daisuke falling into this in regards to his unrequited love for Risa. And Mio Hio for Daisuke.
Louise tries to do this when she finds Saito kissing Princess Henrietta after she confessed her love for him and thought he felt the same way, it turns out she was mistaken and he deeply regrets his actions going as far as saying that without Louise by his side his existence is pointless; so they get back together.
Every girl that was in love with Saito does this in the final episode of the anime except Louise who's his bride.
The Yuki Fan Club is rebuked for not wanting this, especially since their non-reciporated love would only make him loathe them. In the manga, their leader Motoko gives up on Yuki.
Late in the manga it's revealed that Momiji has romantic feelings for Tohru, but he's also aware of the Unresolved Sexual Tension between Tohru and Kyo. Even after Momiji's curse is broken (meaning he can hold Tohru without transforming) he decides to step aside. He does, however, warn Kyo that he'll make a move if Kyo doesn't try to move forward with Tohru for too long.
In Future Diary, Yuno, of all people, does this in later chapters. She has near-death experiences in chapters 22 and 23, and both times she was ready to die in order to save Yukiteru from the 4th—either from blowing herself and the 4th up with a grenade or taking a missed shot from Yukiteru while being held as a human shield by the 4th. Later, when Yukiteru's parents die and he swears to kill the rest of the diary holders (and explicitly mentions killing her) so he can become a god and bring back his parents, Yuno, with a smile on her face, responds:
Yuno: I'll die for you whenever you want, Yukki.
Serves as one of the main Aesops for Gankutsuou. Franz teaches Maxamillian that the most important thing when you love someone is to make that person happy, whether you can marry that person or not. Both Franz and Peppo carry through with it, and it's implied that a failure to understand this is where the older generation went wrong and caused the tragic plot. Well, partially. It gets more complicated than that.
Madarame of the Genshiken manga has a secret and rather intense crush on Kasukabe Saki, the girlfriend of his friend and fellow otaku Kousaka. Not willing to risk his friendship with both, he keeps his feelings to himself.
In the manga Ginen Shounen, hero Matataki is extremely skilled and passionate about analog photography. The only thing he loves more is his childhood friend Mirai. As the story progresses and his attempts to win her heart fail, it comes out that she's really always loved him, but after seeing him destroy film he'd worked and worked for just he got her sick she decided that he'd be better off without her to hold him back. Made worse when, once he finally convinces her that his love for her is what makes his photos shine, his love rival Koda manages to convince her that staying with him will get him killed.
Even Gintama has one of these moments for Hijikata and Mitsuba.
In Girl Friends this may be the reason why Akko and Mari have trouble facing up to their true feelings for each other.
Itta in Girl×Girl×Boy flat-out says that this is his intention - he'd sure be happy if Fuuka fell for him, but if Riri was willing to be with her, he'd be totally fine with bowing to her.
In the Gungrave anime Brandon Heat left his sweetheart Maria so she and Big Daddy can be together. Some subversion occurred because he never thought that Big Daddy could ever hurt her.
The Blonde in Gunjo kills a man among other things to make the woman she loves happy.
Subverted in Hana Saku Iroha, Igarashi wants Ohana to let go of her co-worker, Ko. So she can date him.
Subverted in Hanaukyō Maid Tai La Verite. Mariel appears to put Taro's happiness above her own, but it turns out that she's doing it because she's been brainwashed since childhood into being his perfect slave...er, maid.
The fourth episode of Haré+Guu Marie attempts to do this for Haré and Guu (complete with a "schoolgirl walking through the autumn leaves" scene). Of course, that's not what Haré was trying to tell her at all. Naturally, when he tries explaining this, she assumes he's just trying not to hurt her feelings, and goes into Love Bubbles and sparkles mode.
Hinagiku chooses not to pursue Hayate because she has befriended Nishizawa who was interested first. She has so far made certain that Hayate returns Valentine's Day chocolate to Nishisawa; and has dressed up as a Power Ranger to stick her arms in frogs and stand on a tall building despite being afraid of heights. Hina even 'forces' Nishizawa to go deliver the correct chocolates to him to convey her feelings (Ayumu had given him 'obligation' chocolates, and then run away, but had intended on giving him 'romantic' chocolates). Subverted later as she does pursue her feelings for Hayate and is even encouraged by her friend Nishizawa (sort of a friendly competition).
Athena plays this role (even though there isn't a counterpart romance, yet) after she's been saved, hearing Hayate's words of admiration for Nagi.
Nishizawa works for Hinagiku's favor as early as Hina admits that she likes Hayate. Ayumu manages to convince Hayate to walk her home, and their conversation is about how Hayate feels about Hinagiku, which then gets related back to her. Almost as if both girls are frustrating the other's attempts to work this trope.
Miki. Having stated pretty clearly that she likes Hinagiku, she plays out Batman Gambits that seem to be pointing Hinagiku into a relationship with Hayate.
Subverted in-story in Heart Catch Pretty Cure. Ban has created a manga about Cure Blossom and Marine in which a story had Blossom discover Marine was in love with a guy named Ken, so she decides to help the two get together, only for her to realize that she had fallen for him as well. Ban has a brain fart and can't figure out what to do next, so Tsubomi and Erika act out an ending where they both drop their crushes and decide that their friendship and being Precures are much more important. He loves it and runs with it.
Played with in Higurashi: When They Cry. Rena has a very obvious crush on Keiichi, but Mion has an even more obvious one. Rena says she was perfectly fine with Keiichi giving Mion the doll. Then again, Rena is pretty nice.
Towards the end of the manga, Inuyasha realizes that he'd rather Kagome live forever in her world and he remain in his if it only means she'd be able to live in safety and peace. At the end of the manga, Kagome goes back to her world and the passage between their worlds closes, leaving them in their own worlds and separated from each other. Inuyasha puts a brave face on it, saying it's for the best since she will be safe and at peace. After three years, the passage reopens again, reuniting them permanently.
In a filler episode, when wealthy nobleman Kuranosuke Takeda proposes marriage to Sango, Miroku spends most of the episode conspicuously refraining from offering any input whatsoever - much to the frustration of Shipper on Deck Kagome, who badgers him about it until he calmly points out that if it would make her happy, Sango would be much better off marrying Takeda than she would be continuing on with them on their quest to kill the Big Bad.
In Junjou Romantica, Usagi trips over this trope when Misaki's brother (who doesn't know Usagi and Misaki are lovers) persuades him that Misaki would be happier living with him and his wife, since Misaki's never really known what a proper family is supposed to be like. Because Misaki has never been able to just ask for what he wants, he goes along with this, even though it's making him miserable (though Usagi figures it out in one of the series' most touching scenes).
In Kaleido Star, ex-magician/now businessman Kalos Eido has been in love with his right-hand and companion Sarah Dupont for years, but since Sarah ditched her singing career to work with him, he feels horribly guilty and doesn't dare to ask her out.
During the ending chapters of the manga version of Kashimashi: Girl Meets GirlYasuna says she only wishes for Hazumu to be happy, and thus she does not mind if Hazumu chose Tomari instead of her. That she ends this dialogue in tears might undermine her words, however.
A platonic example in Kiznaiver, when Maki asks the group why they would try to help the girl who made them go through all the events of the plot, Nico headbutts her and pulls off an What the Hell, Hero? against her. She states that, she herself does not like Sonozaki, but Katsuhira does, and if her friend wants to help the girl he likes, then even if they don't like her, it's their duty as friends to help him. The finale implies that this got through all of them and they are trying to fit Sonozaki into their group.
Up to Eleven with Mutsumi in Love Hina. She's been in love with Keitaro ever since she was a toddler, but she purposefully threw a game of Rockpaperscissors when she competed with Naru to see who would form a Childhood Marriage Promise with him. She continued to ship the two of them when they met again 15 years later, even though Naru — and to a lesser extent, Keitaro — didn't even remember the promise. Naru didn't even like Keitaro for most of the series and it would have been easy for her to win Keitaro's affection, but in her mind their happiness was more important.
Nachi and Kaya in Mugen Densetsu Takamagahara: Dream Saga both concede to Yuuki.
In the seinen My Balls, Minayo has finally encountered someone who doesn't get freaked-out by her drunk nymphomaniac side, however he's fallen in love with Elyse at this point. For a comedy/ecchi/romance manga it's kind-of a Tearjerker to see Minayo comes to work with her hair cut and Elyse arrives and admits she accepts Kouta's feelings in a stealthy love declaration. Kouta was after all the first person to accept this side of her.
The early chapters of My Love Story!! feature Takeo trying to make sure Rinko Yamato gets together with his best friend Suna, despite his own feelings for her. Fortunately for Takeo, Yamato likes him, not Suna. Takeo is simply very slow to realize it because of a lifetime of seeing the girls he liked prefer Suna. Later, Suna's sister, older by about seven years, is revealed to have liked Takeo since they were children but held off until the age gap was less of an issue. She is shocked to find he has a girlfriend of his own but after seeing them together opts to stay out of their way.
My Monster Secret: Nagisa is very much in love with Asahi, but he's already in a relationship with Youko. She tries to take this approach to the situation, but it turns out that it's a lot easier in theory than it is in practice. She does her best to support their relationship (as she's one of Youko's best friends), but is constantly conflicted between her own desires and her desire for her friends to be happy together. Shiho invokes this more successfully; her main issue was admitting to herself that she liked Asahi, and once she comes clean she's able to let go.
In the second half of Nana, a really tragic case of both halves of a separated couple failing to reunite because they think the other would be happier without them forms the central conflict.
Jiraiya and Tsunade also fall to this trope. After Tsunade lost both her little brother and her lover, Jiraiya never took that chance to get a Relationship Upgrade even after Dan was out of the way. Choosing to just stay on a friendship basis with Tsunade and support her in any way he can besides being lovers, fearing that becoming attached to her would just break Tsunade's heart again if she lost him. And she did.
It's revealed in Kakashi's ANBU Arc that Might Guy was the driving force behind Kakashi being released from ANBU. After watching his best friend become more emotionless and depressed, Guy begged the Third Hokage and Danzo to either allow Guy himself to join ANBU, or release Kakashi from it altogether. Both refused to allow Guy to join, stating that he was far too exuberant and kind-hearted to ever make it in ANBU, but ultimately agreed to discharge Kakashi and make him a jounin instructor instead.
Of all people, Karin is revealed to have done this in the end, by getting over her obsession with Sasuke. In the Post-Script Season, Naruto Gaiden, she even quotes the trope's name when asked about her past feelings for him, and it turns out that she was the midwife that helped deliver Sasuke and Sakura's daughter, Sarada, and that she also managed to strike a friendship with Sakura.
Ouran High School Host Club has this in both the anime and the manga. In the anime Eclair lets Tamaki jump off the bridge after Haruhi. In the manga Kaoru tells Haruhi that he loves her, but that he loves his brother more. In the end he tells Hikaru he'll step out of the battle for Haruhi's heart and support him in trying to win it. And, Hikaru tells Tamaki to finally realize his feelings for Haruhi because he wants to fight for her on equal ground, even though he would have an advantage with Tamaki still Oblivious to Love.
In chapter 76 Tamaki has had to cut all ties with Haruhi at his grandmother Shizune's wishes. Haruhi took it a bit hard initially, skipping school to think. This short dialogue goes on while Hikaru and Kaoru go to Haruhi's apartment to drop off her bag:
Hikaru: By the way, don't you think it's good? If the rift between Tono and Haruhi opens more, thinking carefully about it, it will be all to my advantage. Kaoru: Hika—!!'' Hikaru: Just joking! ... Don't you think it would be a waste... if I said that I don't really wish for this to happen?
Kasanoda. He protected Haruhi's secret even if that made people think that he was gay, and gave up his first love without even really declaring it so it wouldn't cause problems for Haruhi. The anime version has Umehito Nekozawa crawling off into the dark, saying some variation of this line... referencing his beloved (much) younger sister Kirimi, who had just deemed Tamaki her older brother... keep in mind that Kirimi thought Umehito was a monster her entire life.
Platonic cases recurring happen in the Pokémon anime, in which trainers release their Pokemon so they can achieve happiness elsewhere. Ash released his Butterfree so he could mate, as did Jessie her Dustox (the latter was an exceptional case since Dustox really didn't want to abandon Jessie). Cases are also recurrently attempted but refused due to the Pokemon's Undying Loyalty, Ash's Pikachu, and Meowth, Wobbuffet and Inkay of Team Rocket were all given options to leave their trainer for brighter destinies but pointedly refused.
Another (presumably) platonic example involves Jessie and James. After Jessie falls for a doctor and thinks about leaving the team, James decides that he shouldn't get in the way of her happiness. Jessie rejoins Team Rocket when it becomes clear that her crush loves someone else.
Volume 3 of Poor Poor Lips has Ren learning about the cause of Nako's debt and deciding to do something about it at the cause of her own chance to live a happy life with Nako. She tells Nako through her goodbye letter to take this opportunity to make all of her dreams come true. However, what Nako really wanted in the end.... was Ren.
In Puella Magi Madoka Magica, This is the foundation of Homura Akemi's actions. However, The moviedeconstructs it- Homura decides that if her beloved isn't going to let herself be happy, then she'll just have to make her happy. And Madoka already was happy as a goddess, but poor communication between the two meant that Homura didn't know that.
Queen's Blade: Hide & Seek presents an incestuousLes Yay variation of the trope with the Vance Sisters. Which has the eldest sister, Claudette, being in love with her younger half-sister, Elina, while unaware that the feeling was mutual, due to Elina's love/lust for their other sister, Leina. Thus, when Elina falls into a state of depression after being defeated by Leinanote Leina had told Elina she loved her, during their semi-final bout of the QB Tournament, to create an opening to attack Elina; costing her the match and her only opportunity to bring Leina home with her, Claudette resolves to defeat Leina on her behalf and force her to return home, for Elina's sake. Except she gets defeated, and is shocked when Leina tells her she shouldn't hide her feelings for Elina. Which is when she finally realizes her love wasn't unrequited after all.
Disturbingly enough this happens after Ranma falls in love with Ryōga (long story, don't ask) leading to the bizarre scene of Ranma willingly kneeling down to allow Ryōga to kill her as Ryōga is so disturbed and horrified by the situation (and wants to kill Ranma anyway). Love potion stuff is scary.
Ranma does this in the manga after Akane slaps him in order to protect Shinnosuke from him in a fight. At that point, he's completely convinced she's in love with Shinnosuke, so he tells her goodbye and leaves, thinking that he'll never see her again. In the manga, this is milked for all the angst it's worth, whereas in the anime, a lot less focus and time are spent on this trope. He tries to do the same exact thing later on in the arc. When they're all out of danger, he tells Shinnosuke to take good care of Akane and attempts to leave them together once more. Considering he's the Crazy Jealous Guy type, this is actually rather significant.
Re:Zero's Rem devotedly supports protagonist Subaru, holding his happiness as her top priority, even though she knows his love already belongs to Emilia.
Subverted in Revolutionary Girl Utena in regards to the Love Triangle between Ruka, Juri, and Shiori. Whereas Juri is struggling with her unrequited love for Shiori, Shiori believes Juri is making fun of her and only associates with her out of pity, leading to extreme bitterness, making Juri believe that her cold demeanor and fencing skills are unlikable assets. When Ruka arrives after recovering from illness, he dates Shiori for a short spell, sleeps with her, and uses her for a duel against Utena. It turns out that he used his duel to humiliate Shiori and call her out on her behavior, and then he breaks up with her in front of the entire school. But even if he did intend to help Juri realize that she had hurt herself a lot... he does terrible things to both her and Shiori - aside of ruining Shiori's standing at school when he could have just called her out in front of Juri, he sexually assaulted Juri as well.
Mamoru did a form of this in the second series, in which he was receiving rather disturbing messages that Usagi would die if they continued to be together and he forced himself apart from Usagi.
In one episode of the first season, Minako had left England, allowing her big-sister figure and her love interest to be together after seeing them cry in each others arms because they thought Sailor V was killed in an explosion.
For Shi Ryuuki in Saiunkoku Monogatari, wanting his beloved to be happy means bootstrapping his country's progress toward gender equality ahead about a century, making it possible for women to serve as government officials so that Shuurei can fulfill her lifelong dream of doing just that. Conveniently, this also turns out pretty well for Saiunkoku as a whole.
In Sakende Yaruze!, Misao pulls a form of this when she leaves Shino after she gets pregnant to not get in the way of his potential career. Nakaya, their son, does the same thing 17 years later when, after coming to live with Shino for a while, he decides to move out to make way for Tenryuu, his father's Love Interest.
There's the resolution to the Karasuma/Tenma/Harima arc, which ends with Harima driving Tenma to the airport so she can join Karasuma in America, which also allows him to indirectly confess to her after 20-odd volumes of the manga.
Also, there is another instance towards the end of the manga where Max, Eri Sawachika's childhood friend who invokes this trope when he convinces Harima to stop Eri's arranged marriage.
In S Cryed, Scheris' last moments can be considered part this, part Heroic Sacrifice. She knows damn well that Ryuhou loves Mimori, not her, but she can't stand to let him die, even if that means losing her own life and another woman getting him. Possibly subverted in that Ryuhou later cites her death as an example of why it's a bad idea to love him, when he tells Mimori that starting a relationship won't be happening.
Serial Experiments Lain toes the line between text and Subtext with a lot of Lain and Alice's relationship, but it's hard to read Lain deleting herself from existence for Alice's peace of mind, arranging things so that she can marry her high school crush, and spending eternity watching over her from the Wired in many other ways.
In Sgt. Frog, the normally cheerfulNinja Koyuki once wished to be an ordinary high schooler. Without her ninja skills, however, she was no longer able to see her friend Dororo. Still, Dororo was perfectly willing to let her live an ordinary life, even if it meant she'd never notice him again.
SHUFFLE!: A possible interpretation for the acceptance of three of the other four girls of Rin's decision to choose Asa Shigure.
Tadase from Shugo Chara! stepped back after realizing the feelings Amu harbours for Ikuto and vice-versa.
Paraietta in Simoun has been desperately in love with Neviril since childhood, but stands aside in favour of Aaeru once she's sure Aaeru is worthy of Neviril.
Lory discusses this in Skip Beat!, when Kyoko admits to him that she has fallen in love with Ren, but will not act upon her feelings. He asks if Kyoko will be able to honestly let Ren be happy with another woman. Kyoko starts by saying she'll use her best acting skills to congratulate him, but can't even finish the sentence before breaking down in tears at the thought of Ren being with someone else, and realizing she can't pull off this trope.
For all her Stalker with a Crush tendencies, Suki × Suki protagonist Touka is prepared to go this route when it looks like a girl is prepared to openly confess her feelings to Ryoutarou with a gift of cookies when Touka herself can only do so while using her invisibility. Then it turns out the girl wanted Ryoutarou to give her cookies to his buddy Utsumi on her behalf.
Midori in Tamako Love Story realizes Tamako's feelings for Mochizo weigh on her heavily and wants to help them in the end by putting her own feelings for Tamako aside.
A very strange example happens in the anime version of To Love-Ru. A cat/wolf-like alien wants to take Saruyama back to her planet as a 'souvenir', seemingly having affection for him after he helps her give birth. In the end however, she goes back alone, wanting Saruyama to be happy.
When Lala finds out that Haruna also has a secret crush on Rito, she decides that Haruna and Rito need to be together so they will both be happy. Although that doesn't mean Lala has changed her plans for her and Rito to also be together.
Tokyo Ghoul and its sequel in particular like to explore this trope on multiple occasions.
Touka and Tsukiyama argue over whether they should take action to help Haise Sasaki regain his memories. She wants him left alone, because she'd rather lose him forever than take away his chance for a happy life.
Seidou Takizawa opts out of the Love Triangle with Amon and Akira, leaving immediately after he's managed to save them both. During battle, he even draws strength from imagining watching them gaze lovingly at each other.
"Smile, Mado. I'm bringing Amon home."
It's deconstructed to some extent in Toradora! with the platonic versions that Taiga and Minori attempt. Each of them are aware of the other's feelings for Ryuuji, and try to hook Ryuuji up with them despite their own feelings for him. Eventually, Minori tires of the situation, admits her feelings for Ryuuji, and demands that Taiga do the same. When Taiga cries that she only wanted Minori to be happy, Minori responds that her happiness is not anyone else's responsibility, and that assuming responsibility for someone else's happiness over one's own is actually quite self-centered and arrogant. This ultimately leads to Ryuuji and Taiga getting together.Minori also pulls the romantic version with Ryuuji and pushes him to be with Taiga, as she knows that he loves her too.
All Tatsuya in Touch wants is for he, Kazuya and Minami to be happy together, even if it means letting Kazuya have Minami. Even after his tragic death, Kazuya still remains the elephant in the room, as Tatsuya continues to think himself unworthy of Minami and feel guilty about "taking" her from his brother.
In the beginning of Kotoura-san, Hiyori was jealous of Haruka that the latter won over Manabe despite being a New Transfer Student while she became a Hopeless Suitor, eventually asking a few thugs to attack Manabe, causing him to be hospitalized. Haruka then ran away out of guilt after reading Hiyori. After a week of an obviously unhappy Manabe, Hiyori planned on bringing Haruka back.
What Reito from World's End Harem originally intended for Erisa, he only confessed his feelings to get it out of his heart before his imminent death by succumbing to multiple sclerosis, urging her to find someone else, reminding her that she is very popular and has been confessed to by a popular senpai not long ago; Erisa doesnt comply to Reitos wish and says she will wait for him to be cured during cryostasis, in hopes that their advanced society will find a cure during his cold sleep.
In Yu-Gi-Oh!, Yugi, believing that Yami Yugi was the only version of him Anzu Mazaki was attracted to, once tried to switch with him while he was in a private romantic moment with her, although he himself had a huge crush on Anzu. She stopped him, insisting that his regular self was perfectly fine for her.
In Yurara, both Mei and Yako attempt to do this during the course of the story. Neither of them handle it particularly well.
Alluded to several times in Zetsuai 1989: Kouji feels guilty for not feeling this way about Izumi. But despite his frequent statements that he'd like nothing better than to lock Izumi away from the world and have him all to himself, his actual behaviour is closer to this than If I Can't Have You....