A person (usually The Hero) has her or his entire motivation built around protecting another person. Most of the time, it's his or her Love Interest, but it could also be her or his little sibling, or child, or parents/parental figure . In Anime, the sentence "Zettai Ni Mamoru!" is likely to get used - if not spoken aloud, then thought.
Almost every time, some sort of complication will arise from this situation.
The protected person is a Badass and quite capable of looking after her- or himself, most of the time. The protector has a hard enough time just keeping up with them, much less being of any use, and will often chastise themself for failing to live up to his perceived duty as protector. Inevitably, however, the protected will get into trouble, at which point the hero's Hot Blooded-ness and Heroic Resolve will manifest and s/he'll become suddenly competent as s/he leaps to save her.
The protector fails to protect the protectee, and s/he winds up dead, his or her Greatest Failure. In this case, the relationship is more likely to be part of the backstory. It might have been the former protector's Start of Darkness, as s/he went over to The Dark Side while seeking revenge, or went mad while seeking to bring the protected back. Or maybe the protector just cracked and turned into a Death Seeker. If the protected person survived despite his failure, the effects will be less severe, but all of the above can still occur — there's just a better chance of redemption later on. If the protector has to protect multiple people, and fails at doing so, then they're effectively a Doom Magnet and tend to suffer Survivor Guilt.
The protected person is normal, and the protector is not... and the main reason the protected is even in danger is that someone is hunting the protector. Thus, the protector feels compelled to part with the protected, or run away from any other responsibilities to keep her safe. It almost never works. Note that most of the examples in It's Not You, It's My Enemies do not apply here — for it to qualify, protecting that person has to be the character's main driving motivation — so, for example, Spider Man wouldn't qualify, since he knows he has a greater responsibility to protect the entire city, and the world. (And let's not even mentionOne More Day...)
The protector protects their person, but at the cost of his/her life, or nearly so. If the protector dies, it could be a Start of Darkness for the protected, particularly if the protected person has any kind of power. If the protector survives, it's more likely to work as a Berserk Button, but it might also compel the protected to try and push him/her away so s/he won't get hurt again.
The protected person turns out to be The Mole, or just plain bad news. The protector likely won't see this, even if other try to tell her/him - and it's fairly likely that s/he won't realize it 'till the protected person finally stabs him in the back. It can turn out in a lot of different ways, but it's usually quite tragic. If the protector kills their (former) protected in response, it'll probably turn out that the traitor was acting under duress, and the protector will be swallowed by grief and regret. If the protector dies by the traitor's hand, s/he'll probably realize that s/he really did love her/him, and be swallowed by grief and regret. But if the protector continued to insist on protecting the protected, even after s/he's shown her True Colors, s/he might realize that s/he really does love him before s/he kills her/him, and be redeemed by love...
'Protecting' turns out to be more complicated and morally ambiguous than it sounds. Maybe the protected person has some sort of weird power that makes a lot of people fear them, or maybe the very layout of the world makes it impossible for them to live in peace. The hero may be forced to fight and kill more-or-less innocent people who attack the protected person out of fear, or orchestrate rebellions and war in order to change the world for their love's benefit — either way, there's bound to be a lot of victims, and the 'hero' will start to look less and less heroic...
In the past, the protected person did something for the protector. Either saved her/his life, pulled her/him out of trouble, gave her/him something s/he needed, befriended him/her when nobody else was willing to, etc. So the protector cherishes said moment in which the protected was there for her/him, feels indebted to them, and swears to protect them as a way to pay them back for their help. Debts must be paid, after all... even if it involves pretty much going to Hell and back to not owe that person anything.
Naturally, not all cases will fit neatly into one of these categories, and of course, there are cases where there isn't really any major complications - just someone protecting another person from the Monster of the Week, for as long as it takes.
Related tropes are numerous. Effectively, it is a subtrope of The Protectorate and The Champion. Bodyguard Crush is when the protection comes before the emotions. The Dulcinea Effect is when this absolute dedication pops up all of 10 seconds after he first sees her. Mama Bear and Papa Wolf are when it's a parent protecting their child. This trope is part of the job description for Lady and Knight.
Warning! Some of these examples will be spoilers solely by virtue of which 'type' they get placed under!
Declaration Of Protection
Examples:
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The protected person is a Badass themselves.
Anime and Manga
Kekkaishi. Yoshimuri has sworn to protect Tokine, but while he has a great deal of raw power in the art of Kekkaishi, Tokine is vastly superior in terms of skill and refinement - so he can barely keep up with her, and usually ends up needing her help in a fight, rather than the other way around. (In truth, they're pretty evenly matched, but she's too proud to admit it, and constantly belittles his lack of skill - which he takes completely to heart, causing him to often convince himself that he was no help at all, even though his raw power was as important in defeating the Monster of the Week as her technique.)
Claymore could be interpreted as having at least two of these.
In Digimon Adventure, Takerupromised to Sora that he'd protect Hikari. Fast forward to Digimon Adventure 02 and Takeru still takes that promise very seriously even if Hikari by now can already take care of herself (provided an Eldritch Abomination isn't messing with her head). To wit, he is seen putting himself protectively in front of Hikari (episode 3), seemed angry at himself for accidentally leaving her stranded in the Digital World (episode 7), and doggedly searched for her when she was taken by the Dark Ocean (episode 13).
In Dragon Crisis, Ryuuji does this for Ai. She is able to read his thoughts due to magical earrings she was wearing at the time. Although she learns that he's scared, he still tries to protect her, long enough for the Big Damn Heroes to show up to help him.
Gin's relationship with Rangiku in Bleach mixes this and "Protecting her gets complicated". They met when they were Street Urchins, she was once severely beaten up by Aizen's cronies, then he promised to become a Shinigami so she wouldn't cry again... but not only she became an Action Girl in her own right, to protect her...he became the biggest Jerk Ass in Soul Society. Then, having failed to defeat Aizen, he dies, regretting how he couldn't avenge her and thinking he should have truly apologized to her. And then, we see her cry her heart out over his lifeless body...
Also, Tia Harribel towards her Fraccion. In the wild, she lived as close as she could to a life of non-violence and starvation to defy the Social Darwinist laws of Hueco Mundo. Since then, she has been motivated to fight by a desire to keep her few friends from dying... and these friends are her Amazon Brigade.
Shuuyu has this problem in Ikki Tousen. He's a skilled fighter, even amongst his fellow 'reincarnated Romance of the Three Kingdoms warriors', but he doesn't have quite the same level of world-shaking power as his Bodyguard Crush, Sonsaku. The fact that Sonsaku is Oblivious to Love and a fight-loving Blood Knight does little to improve his situation - her first reaction to him declaring his intent to protect her even at the cost of his own life, is to ask if he's eaten something strange...
The eponymous character of Kenichi: The Mightiest Disciple has sworn to just about everyone in earshot that he'll become strong enough to protect the Love Interest, Miu. Naturally, since she's the granddaughter of the man who owns the dojo that Kenichi attends, she's a far better fighter than him.
Guts from Berserk falls into both the first and second categories listed above. He did everything he could to save Casca during the Eclipse, up to and including chiseling off his own left wrist, and she was still raped in front of him by Femto. She survived, but her mind was completely gone. Her fate is most of what fuels his post-Eclipse Unstoppable Rage during battle and continuous Roaring Rampage of Revenge. Later, when Guts puts said roaring rampage on hold, his top priority is to protect Casca above all else - even from himself.
While rather understated (as in it's clear to the reader, but he hardly shouts about it) it's plainly one of Soul's motivations for protecting Maka. He insists its because it's his job as a Weapon. Fits whether or not you view them as a canon couple. Jackie shows a similar angle towards Kim with aforementioned connotations. Though the basic sentiment extends to pretty much every Weapon/meister team and works both ways.
While Akira and Mina generally fit in this category, it's complicated by the fact that they're pretty much a match for each other. Though to be frank if Mina had to watch her own back all the time she'd have absolutely no time left to, y'know, rule, and Akira has "protecting her" in his job description.
Another interesting point is that if we reverse the roles, then Mina herself clearly fits the last category. Akira is her anchor in the merciless world around her, and their childhood promise is the main thing that holds her still on the Slippery Slope.
In Pokémon Special, admittedly, it takes only a little while for Lady Berlitz to become an Action Girl, but nevertheless, Dia and Pearl swear to protect her with their lives after they learn the truth about the whole situation surrounding her though Dia did have a good idea of what was really going on the whole time and when her real bodyguards get banished into the Distortion World.
In Code Geass, Lelouch does this for Kallen first by lying to her about using her in order to have her spared from going down with him when the Black Knights turn on him, and later by keeping her locked out of the Zero Requiem.
Deconstructed in Ayashi No Ceres. Shiso and Ceres have an Inter-Species Romance-type marriage, with him as a human and her as a Magical Girl of sorts. After they're attacked and he cannot help her fight off their attackers, Shiso decides that he doesn't want to be The Load and asks Ceres to give him a part of her powers, so he can fulfill this trope. But said powers drive him literally crazy for Ceres, with dire consequences.
Zenkichi towards the protagonist Medaka. To become strong enough to stay by her side, he's become a capable fighter, though Medaka is still the strongest character. It's partially as an emotional anchor, since she was traumatized by a past failure. Averted as of chapter 117, when Zenkichi realizes that Medaka doesn't need a protector.
Angel Beats! subverts this with Hinata and Yuri/Yurippe here seeing as they're both immortal.
In Sekirei, Minato often ends up doing this for the Sekirei he eventually becomes their Ashikbabi for. This helps win over many of them, such as Musubi, his first Sekirei, Kusano, and later Tsukiumi.
Though it doesn't start out this way, protecting Hatchin becomes one of Michiko's main motives in Michiko To Hatchin. Later this trope is touchingly inverted when Hatchin proves to be pretty badass herself and says, almost line-for-line, that she will protect Michiko.
Kurando's primary motivation in Popcorn Avatar is to protect his twin sister from the Asura and maintain a world where she can safely live in.
In x 1999, YuzurihaNekoi verbally invokes the trope in the manga as she and ArashiKishuu speaks about the guys they like. The dude Yuzu wants to protect? Shiryuu Kusanagi, a man who not only is more than twice her age, but is a member of the Japanese Self-Defense Forces and quite the badass among the Dragons of the Earth.
Similarly, Lady of War Arashi's suitor is Sorata Arisugawa, a Religious Bruiser and fellow Dragon of the Heaven. Upon seeing her up close for the first time, Sorata decided to protect her. This is because he's prophesied to die to protect a woman, he knows it clearly, and he thought he'd at least die for a pretty girl and chooses Arashi at first due to her Aloof Dark Haired Girl traits. And from then on Sorata gets Arashi to gradually defrost, and they fight together... and get together. But things go From Bad to Worse.
In Girls Und Panzer, Maho's ultimate goal in living up to the standards for the Nishizumi heiress is so that her younger sister Miho can live and do tankery as she wishes, without having to take up the responsibility in her stead. It takes six years, from near the end of the prequel manga to the last episode of the first series, but Miho ultimately finds a way of Tankery that she can do, and Maho is very pleased with this.
Maho: As long as I'm the heir to the Nishizumi school... Miho will be free.
In Fullmetal Alchemist,Friendly Sniper Riza Hawkeye spends all her time Bodyguarding A Badass. It is her sworn duty to protect the Flame Alchemist, Colonel Badass Roy Mustang; she even tells the young Winry Rockbell that this is the whole reason she's in the military despite her own dislike of it.
Literature
In Suzanne Collins' The Hunger Games, Peeta devotes himself to this cause for Katniss, who spends most of her time in the series kicking asses and taking names. He generally devolves into The Load in any situation which would traditionally require him to fight, meaning that she has to do the protecting and thus doing a great job inverting the trope.
Though to be fair, the reason why he becomes The Load in the first book is because he saves Katniss' life by fighting off Cato and gets a sword to the leg for his troubles. In the second book it's less heroic, but getting electrocuted would slow most people down.
Live-Action TV
River Tam in Firefly is a subtle distinction she really did need and want Simon's protection, but that was because she was so erratic that she needed a stabilizing influence even with her powers.
She wanted his love even more then his protection. Despite her powers and chaotic nature she seems to have always wanted to have someone to look up to. And Simon, despite his unimpressive appearance had an assertive personality and must have given other incompetent surgeons besides the one in Ariel cause to regard their lives as a burden.
River: You take care of me. You've always taken care of me! *Beat* My turn.
Another Joss Whedon show: nearly everything Paul Ballard does on Dollhouse is to protect Echo...even before he actually meets her.
In Chinese Paladin, Xiaoyao marries and swears to protect Ling'er. He takes this vow very seriously although initially she is far a more powerful combatant than him and all she needs is his emotional support. However, as the series progresses he Takes A Level In Badass and it becomes Just That Simple between them.
On The Vampire Diaries, Stefan, who is the hero, devotes his immortal, undead life and makes constant sacrifices (including sacrificing himself or risking his life) in order to protect and save Elena, the heroine (or more like damsel in distress) from possible harm and dangers of the supernatural in the town of Mystic Falls.
In The Power Of Three he tells a levitating alien cube that earth and its people are precious to him, and that he will defend them to the death, if need be.
In The Bells Of Saint John, after he recovers Clara Oswald's consciousness from a Spoonhead android, The Doctor sends a message over the Wi Fi network, "Under My Protection".
He declares this again in Nightmare in Silver about the young children that the Cybermen have begun to convert.
Video Games
Arado Balanga from Super Robot Wars Original Generation 2 is a pretty good Mecha-Pilot, objectively speaking - but as a graduate of 'The School', he's at the bottom of the heap - especially compared to his partner, Seolla, who's one of the best, period. But he's sworn to protect her, and protect her he does - whenever she ends up in a pinch, he goes Crouching Moron, Hidden Badass, whether that means fighting off an otherwise-supreme opponent, or taking a bullet for her. Sometimes both.
An odd twist on this for both Knights of the Old Republic if you're playing female. In the first, Carth knows damn well you could skewer him on a lightsaber and not muss your hair. Still does not stop him from admitting that trying to protect you is his reason to live after Saul Karath dies painfully. In the second game, Atton's overt about it. Bao-Dur is more subtle, but still frighteningly loyal to his "general." In both Carth's case and Bao-Dur's, the "protection" they offer is more or less trying to act as the Morality Pet for a female Player Character in order to help prevent her from falling to the Dark Side.
Persona3: It's a gender reversal, and it's after everything is over (until FES), but Aigis sort of qualifies with her wanting to protect the main character...who can certainly fend for himself.
More literal in the end of the portable version, where the gender roles are the norm for this trope. Also note that many of the Female Protagonist love interests also fall under this.
Tales Of Graces: Main characters Asbel and Sophie actually argue over who gets to protect who, until Asbel challenges Sophie to a footrace to settle the matter...and loses.
Probably for the best, though. Sophie ends up saving the group from certain death more than once throughout the game, and is canonically one of the most powerful fighters in the party ( Arguably THE most powerful member until about halfway through the main arc, when Asbel is given an opportunity to defeat her in single combat).
Visual Novels
Fate/stay night.Emiya Shirou. He does this twice. In Fate, he does this to Saber, despite Saber being motherfucking King Arthur. (To be fair, he HAD no idea who she really was AND had watched her get totally curbstomped by Hercules.) Fortunately, he's called out on this and eventually it gets deconstructed in the Unlimited Blade Works route (the second example), where it turns out that Shirou has a massive case of Survivor Guilt that causes him to totally disregard his own safety. Heaven's Feel also plays with this trope by having Sakura be, from Shirou's point of view, totally helpless... then you get closer to the end and she turns out to have an absurdly powerful Superpowered Evil Side. Shirou promptly modifies his definition of "protect Sakura" to mean "get rid of Sakura's Superpowered Evil Side."
Web Animation
Kerry from DSBT Insani T makes it a point that no one shall harm Shawn, although the latter is certainly capable of protecting himself.
Kerry: Nobody harms Leader Shawn!
Western Animation
Avatar;The Last Airbender- when Sokka was still feeling guilty after losing his last girlfriend, he decided to make sure nothing happened to his other love-interest Suki. Of course, being an Action Girl, Suki is mostly bemused and slightly insulted by this- and eventually reveals the only reason she went with them was to protect Sokka.
Failed To Protect Them
Anime and Manga
Code Geass gives us Suzaku and Euphemia. Initially a fairly straight and uncomplicated 'knight and princess' relationship, Euphemia's death at the hands of Zero pushes Suzaku off of his white horse, driving him into much more questionable actions, such as selling out his oldest friend to his worst enemy or releasing a powerful nuke in battle... and, in the end, he winds up supporting one of the bloodiest tyranies in history. Led by, you know, his oldest friend.
Konoka and Setsuna's dynamic falls most closely under this, at least initially, but actually covers several variants. While Setsuna is heavily motivated by a backstory incident where she failed to protect Konoka, she also spends a lot of time trying to protect her by hiding the truth about magic from her, thus making it a case of It's Not You, It's My Enemies. Later on, she also very nearly dies while trying to rescue Konoka. Ultimately, however, her absolute dedication to protecting Konoka comes back to the old childhood 'close shave' where they were both lucky to survive. (Oh, and whether Setsuna's dedication edges into the territory of Schoolgirl Lesbians... is left as an exercise for the class.)
Karasu of Noein is basically built around protecting Haruka, typically telling his opponent something along the lines of, "I will protect her with my life." This is because, in his opinion, he failed to protect her future self, though it is implied she willingly did a Heroic Sacrifice.
Ikumi from Infinite Ryvius lost his sister years ago, and was severely traumatized by it... which makes sense, seeing as she committed suicide because of their illicit Brother-Sister Incest relationship. So he's sworn never to fail to protect a woman, particularly one he cares about. When his new girlfriend, Kozue, is attacked and scarred while he was out fighting, it becomes his Start of Darkness as he decided that Utopia Justifies the Means - he'll do whatever it takes to protect her from now on. It... doesn't end well. Either way, that means he fits this subtrope TWICE OVER. Poor guy.
Live-Action TV
The X-Files. Mulder and Scully could arguably fall under almost all of these, but this one is closest. While Mulder was always very protective of Scully, after her abduction in season 2, he snaps and after her return becomes obsessed with keeping her safe. He ditches her several times, much to her annoyance, and even asks her to sit out on cases for fear of her life. Of course, it doesn't help that he makes it obvious that the one way to hurt him is to hurt her, and so this protective streak becomes even more pronounced after she is kidnapped many times. Eventually, this also turns into "I Owe Her My Life", since Scully is no slouch in the protecting and rescuing department.
Spike showed hints of this after Buffy died in the episode "The Gift".
Video Games
Zig-zagged in Dissidia: Final Fantasy at first Cosmos's warriors (especially the Warrior of Light) make it their mission to protect her from Chaos and his henchmen. In the end she willingly let's herself die in an effort to save them from the cycle of death and rebirth they've been caught in.
Prince of Persia (2008) has the prince play out this trope. He doesn't really care about the lost kigndom, or the Big Bad, or any of that - he's only fighting because Elika DOES care, and she's gonna put herself in harms way with or without him. In the end, she gives up her life to stick the Seal back on the Can of Evil, and he immediately snaps and tears the lid back off to ressurect her again. She is not happy about that.
Sorta invoked in The King of Fighters. One of Kyo Kusanagi's main motivations in the Tales of Ash saga is to make Ash Crimson pay for attacking Chizuru Kagura, his friend and fellow member of the Sacred Treasures Team, and stealing her Magic Mirror. It's really not helped by how Kyo couldn't do anything to stop him.
I'm Only Protecting You From Me
Anime and Manga
In Death Note after Sayu gets kidnapped by the mafiaLight deliberately sets things up so that he can't kill her without incriminating himself.
Video Games
A twist on this can occur in Suikoden II. The Hero has somehow wound up leading La Résistance against The Empire, and his adopted sister has, naturally, wound up getting dragged along for the ride, despite being just about the only playable character NOT listed in the stars as one of his 108 destined companions. When she finally admits that she'd prefer to live quietly together, you have the option of agreeing with her, running away from your army and responsibilities along with her, thus demonstrating an alternate solution to the problem. The result is somewhere between a Non Standard Game Over and a... well, Not All That Bad Ending. You actually DO get away, and live quietly together in a cabin in the woods somewhere far from all the war and strife... but of course, La Résistance fell apart, The Empire triumphed, and all your other friends probably died.
Web Comics
Sluggy Freelance, of all places, has an example of this. Torg may have a lot of diversions, but there's only ONE thing he's actually SERIOUS about - and that's protecting Zoe. In an alternate universe overrun by demons, he soon gave up on trying to run La Résistance (since everyone there are Perfect Pacifist People), and instead just concentrates on keeping Alt-Zoe fed and away from trouble. Back in the real world, he forces her away so she won't become a target for Stalker with a Crush Oasis. With... mixed success.
Taking a Bullet for Them
Live-Action TV
Steve Jinks, Warehouse 13 has an interesting combo of three, He has a dead big sister that he sees in Action Girl Claudia, his partner, after she saves his life in the most hilarious way possible. This lead him to decide to go undercover to protect her because he couldn't save his own sister, which in turn, gets him killed. He gets better.
Video Games
Super Robot Wars Gaiden. Ricardo takes a bullet for Tytti, saving her life... but leaving her Allergic to Love due to losing him.
This is one possible outcome at the end of Dragon Age: Origins: if a female Grey Warden has a romance with Alistair, he will refuse to allow her to sacrifice herself to kill the Archdemon, taking the choice out of her hands and doing it himself unless she takes the precaution of leaving him behind at the gates before heading to the last battle.
Resident Evil 2, and quite literally, in the case of Leon and Ada. Crossed with The Mole scenario.
The Big Daddies of Bioshock are willing to die to protect the little sisters.
Web Comics
Happened in Girl Genius when Lars — a traveling performer previously renowned for his cowardice — threw himself in front of a sword to protect the eponymous protagonist, Agatha. He died, and she went nuts, temporarily going into full Blood Knight mode, and attempting to basically take on the entire army of Wulfenbach singlehandedly. (Well, with a little help from her Mecha-Mooks...) She got over it, with a bit of chemical assistance, but now seem hell bent on making sure nobody else dies for her. (Cue Gil and Tarvek winding up in one of the above-mentioned 'She's an Action Girl' situations, as she works harder to protect them than the other way around.)
The Protected Was The Mole
Anime and Manga
Rurouni Kenshin. Specifically, the 'backstory'. Back when he was still an assassin, Kenshin fell in love with a woman named Tomoe - who was actually a spy planted by the Shogunate to find his weakness and eliminate him. The details are awfully complicated, but after The Reveal, she ends up dead along with her employers, and Kenshin swears never to kill again...
Revolutionary Girl Utena probably fits best under this, and is a very genderqueer example, what with Utena deliberately taking on the persona of a Fairytale Prince. She fights solely to protect the Rose Bride, Anthy... but at the end, it turns out Anthy was in on the whole thing, and was in fact following Akio's will, from being involved in his manipulations behind the scenes to doing everything he told her to . . . EVERYTHING. After this, Utena is severely disillusioned, becoming a Knight in Sour Armor, but comes to forgive Anthy after realizing just how much torment she's been in for hundreds and thousands of years, and resolves to truly save her from more suffering.
Resident Evil 2, and quite literally, in the case of Leon and Ada. Crossed with Take a Bullet scenario.
Protecting Gets Complicated
Anime and Manga
Obviously, Code Geass, where Lelouch's desire to give his younger sister, Nunnally, a 'world of peace' leads him further and further down the path of darkness. When she finally finds out what he's been doing in the name of helping her, she's horrified and becomes an easy prey for Schneizel's manipulations.
Toshiro Hitsugaya and Momo Hinamori in Bleach. As a kid, Momo was the only child in the neighborhood who wasn't afraid of Hitsugaya due to his burgeoning ice powers. As they became Shinigami, he swore that he'd protect her and pretty much kill anyone who ever made her bleed a little... But when Momo was horribly broken and then almost killed by the man she loved, Sousuke Aizen, Hitsugaya tried to avenge her, and was almost killed himself. When Momo got better and reclaimed her Action Girl credentials, she and others were horribly defeated by Allon. And then... Aizen used his powers to trick Hitsugaya and other captains into stabbig Momo to almost death, thinking they were stabbing him.OUCH, it definitely got complicated.
Also, after Karakura is attacked and Orihime is seriously injured, Rukia brings Ichigo to her to apologize for not having been able to shield her, and then Ichigo makes the promise that he will protect her from then on. Considering that later she was forced into a cruel Sadistic Choice that involved her going to the villains's HQ and Ichigo then goes to rescue her, it got complicated and then some more (though later it gets better.). The trope is reinforced when Ichigo brings himself Back from the Dead when he hears Orihime scream in horror for his death at the hands of Ulquiorra.
When Homura Akemi in Puella Magi Madoka Magica was caught in a witch barrier, Magical Girl Warrior Madoka Kaname saved her. She then vowed to help her and protect her in return. She failed, however, and Madoka died. Then Homura made her contract with Kyubey, and specifically hoped to protect Madoka and avert her death. She failed each time, but kept on trying...
At the End of the second Rebuild of Evangelion movie, Shinji, who on this point had pretty much given up on all his hopes, witnesses his Love Interest Rei being eaten by an Eldritch Abomination. He then proceeds to return from his 10-Minute Retirement to rip her directly out of the bastard, claiming that he doesn't care what happens to him or the world, he will DEFINITELY save her. Too bad that his rescue attempt ends up triggering the apocalypse... Thank God for Kaworu's Intervention.
In the third movie this becomes I Failed To Protect Her, as the apocalypse happened and Rei died anyway.
Things start off simple for Melan in Brigadoon: Marin and Melan. His job is to protect the Creis, who happens to become his friend and eventually his Love Interest. Then it turns out that she's not the Creis after all, and protecting her means taking time out from his REAL mission.
A very interesting case happens in Baka and Test. Resident Yandere Shouko is absolutely obsessed with Brilliant, but Lazy student Yuuji, and at first it seems like she's just a crazy Unlucky Childhood Friend. But then in episode 11 of Season 2, it goes into their backstory, and her reasons are explained: Shouko was (and still is) a Lonely Rich Kid, with Yuuji as her Only Friend. At some point, Yuuji pulled a Big Damn Heroes moment to save Shouko from three boys who tried to bully her after she tried to stop them from writing some vicious lies on his PE clothing; he tried to come up with an excuse not to help, but in the end saves her anyway. Although he tries to pass it off as nothing, Shouko is really touched by that action, and she vows to his mother to marry him someday. His mom happily agrees to support her efforts as well... which then sort of helps explain why she tasers him, ties him up, pokes his eyes out when he's looking at other women, and drags him to the movies in chains.
The Sword and Sorcerer team Shannon and Raquel from Scrapped Princess are solely motivated by their oath to protect the eponymous princess, Pacifica. Shannon is the one that most closely match the trope, being a guy and all - since they were raised as siblings, his affection for her is more big-brotherly than romantic, but they are Not Blood Siblings, so it gets... ambiguous at times. As for complications, well, according to a supposedly-infallible Divine Prophecy, Pacifica is 'the poison that will kill the world' - specifically, she will destroy the world when she turns 16. As a result, virtually everyone wants to kill her, either out of fear, religious fervor, or greed for the huge bounty the kingdom has placed on her head. And Shannon is stuck trying to protect her from all that, preferably without killing anyone because he knows that Pacifica would blame herself for any lives lost...
Ian is determined to protect, love, and save Jeremy, but it gets complicated considering Jeremy Vehicular SabotageMake It Look Like An Accident his father, even if Jeremy did have valid reasons...
In Death Note Rem forces Light, under direct threat of death, to adopt this mindset towards Misa in regards to his plans during the events that lead up to the Yotsuba arc.
Fan Works
In the Death Note fanfic Broken Facades Light promises his father he will look after Misa. He didn't count on either of them becoming Kiras when he made that promise.
Video Games
In Nier, the eponymous (assuming you use the default name) character's overriding desire to protect his daughter, Yonah, initially seems perfectly simple... and HE probably never realizes it was anything but. The player, on the other hand, will soon realize - by the second playthrough if not sooner - that he's been doing a LOT of really questionable stuff in order to protect and save her.
In Sands Of Destruction has a gender flipped version of who to protect. Toppi grows an attachment to Kyrie because of his positive ideals and swears to protect him. It's complicated in the since that Kyrie is a Person of Mass Destruction and has the power to destroy the world and Toppi really doesn't want that.
All main routes of Hakuouki lead inevitably to this trope thanks to Chizuru spending a good four years in the constant company of the captains of the Shinsengumi, all of whom, aside from Sanan, develop protective feelings toward her and go out of their way to keep her with them and protect her, even though she's The Load and the Shinsengumi's situation becomes increasingly dire as events unfold. In Okita Souji's route, her Evil Twin Kaoru purposefully exploits the trope with malice aforethought to make poor Chizuru suffer by repeatedly creating situations that inspire Souji to protect her at his own expense.
The King of Fighters gives us Kyo Kusanagi. He is already willing to protect his Girl Next Door girlfriend Yuki to start with, but once he's told that she is a Barrier Maiden and that she was to be used in a Human Sacrifice, his desire to protect her goes Up to Eleven, and later the spirit of his rival's ancestors asks him to protect her among several other things.
It's kind of a plot point in the KOF: KYO continuity. Ever since he was a kid, Kyo deeply wanted to protect his loved ones (in fact, he promises his mother Shizuka to do so when he's as much 8 years old), and that turned out to be one of the reasons why he was so powerful... but after gradually forgetting it in the middle of his turbulent life, he got Brought Down to Normal and then susceptible to being Brainwashed and Crazy by Orochi. Remembering how he began to fight as well as this purpose is what lets Kyo recover his lost powers and shake off Orochi's influence: this is sealed after his Warrior Therapist dad Saisyu undoes a staged Hostage Situation that he built to help Kyo and releases Yuki from an Unwilling Suspension. As Kyo rushes to catchher, his inner thoughts pretty much spell this trope.
Also invoked by Adelheid "Adel" Berstein. He has sworn to himself to be the protector of his younger sister Rose, who also is his only living relative after their dad Rugal's death, and even when he seems to be an Aloof Older Brother he will NOT stop when it comes to shield her from any harm. The main reason why he became Heidern's source of information in XIII was his worry about how oddly Rose was acting around him — and with good reason, since she was Brain Washed by Those of the Past. When she's released from their mind control and collapses, Adel immediately rushes towards her to catch her in his arms.
Other routes also touch the trope, either criticizing it or reaching a compromise between protecting/helping a girl and letting her be when needed. In example, Emi's path shows that Emi does need emotional protection due to refusing to make any deep relationships after her father's death in the accident that claimed her legs, and as long asa Hisao doesn't overdo it, he can protect her broken emotions; and in Rin's it turns out that Rin needs both protection (since she's under very heavy pressure from her well-intentioned but VERY pushy art teacher) and to be understood (because she has big problems on expressing what she feels if it's not through art)
In Little Busters, Kyousuke's reason for most everything he does in the game is to protect Riki and Rin. Specifically, to make them stronger so they can survive without him after a bus crash claims everyone else's lives. Since he won't be around much longer, protecting them also means making sure Riki is able to protect Rin and doing everything he can to encourage him to give himself over to this view completely. In the end, Riki also vows to always protect Rin.
Web Original
Silver in Above Ground wants to protect Lilith and help her return home safely. But he's in complete denial about it all because he knows the desire to protect is an unnatural bewitchment rather than a real feeling. It doesn't help that his pack is in a dire situation and they need money that Lilith could provide if they ransom her off to the Guild.
I Owe Them My Life/Reputation/Health/etc.
Anime and Manga
Hayate the Combat Butler: Hayate (the butler) to his mistress, Nagi. She saves him from his miserable life by paying off his debt to the Yakuza and giving him a home in her mansion and a job as her butler, with a promise to pay her back over years of work. But it never was about the money - the amount means nothing to her absurd wealth. She simply likes him from the start, while his gratitude quickly compounds with a deep affection and interest in her well-being.
There's also the residual guilt from initially wanting to kidnap and ransom her. He was in a desperate enough situation — thanks entirely to his Abusive Parents — that this isn't a Moral Event Horizon, but he still felt terrible about it after he came to his senses.
While Kenshin's devotion to Tomoe in Rurouni Kenshin fits in She Was the Mole, his relationship with Kaoru Kamiya fits here. She gives him a place to stay, emotional support, and the chance to stop Wandering the Earth; as such, he decides to protect her and their friends.
Also by Watsuki, Kazuki from Busou Renkin gave this speech to an opponent (who also gave the same speech), when asked why he was protecting Tokiko. He said that it was because of Tokiko that he was still alive, so he would protect her and fight in her place. Kazuki's situation is actually a combination of type 1 and type 7, since Tokiko is a very capable Action Girl.
In magico Shion is decided to save Emma from the curse of Echidna and faces really dangerous tasks with his extremely powerful magic that he obtain just to do so because... she gave him some bread
Rafael toward Skylar in Gives Light, but in this case, it's "I will protect him." Rafael's father, a serial killer, killed Skylar's mother many years ago, and Rafael feels responsible by proxy.
Live-Action TV
Tin Man A cross of "I owe her," "It gets complicated," and Living Macguffin get involved with the gentlemen who decide to travel with DG. Raw is pretty straightforward. She's a good person, and she was responsible for rescuing him from a nasty death. Glitch comes with because it's preferable to be confused and with someone than confused and alone. But it turns out that he was her mother's trusted and devoted adviser. Remembering who he was and learning who she is just makes him more determined to help. Cain's a mess. He agrees to escort DG and Glitch to Central (Emerald) City because he does owe them that much for freeing him, but the Mystic Man, his former boss, orders Cain to protect DG at any cost - and Cain's too damn honorable to disobey a direct order, especially as it turns out to also be the Mystic Man's Last Request. By the time it's discovered that DG is inadvertently responsible for the Witch's reign of terror, they've become too much True Companions to care.
It's Just That Simple
Anime and Manga
Murder Princess is a straightforward example. It takes Fallis a while to realize that she wants to protect the sweet, gentle (and very, very helpless) Princess Alita, but actually doing so never gets any more complicated than cutting down anything that threatens her or her kingdom.
Film - Live Action
In Iron Man 3, Tony Stark is building new armors in order to protect Pepper Potts, as well as dealing with his PTSD after the events of The Avengers.
"I have to protect the one thing that I can't live without. That's you."
Literature
Memory, Sorrow, and Thorn: Simon has a very difficult time spitting out his affection for Rebellious Princess Miriamele, despite the fact that he has had a crush on her. Part of it is that he feels that she's so far above him socially that his desires will remain unrequited, although he fantasizes about rising to her station or her falling to his. Of course, they keep getting thrown together in perilous situations, and after he's knighted, he resolves to become her champion and protector as a way of dealing with the situation. In the end he discovers that it wasn't their stations keeping them apart at all, but Miriamele's self-doubts and fears of being forced to assume the throne and make a political marriage. And of course he turns out to be the rightful king anyway.
To the point where Simon thinks that Miriamele is too good for him and avoiding him at the end, and he's thinking about how even if he's royalty it's not fair to take the throne that she has more recent claim to and that it doesn't matter if she doesn't love him. Then she bursts in with entirely different worries: that she'll be forced to be queen, and forced into a political marriage, and thus separated from Simon. She's set on running away and wants him to come as her protector. He protects her from a loveless marriage just fine by marrying her, incidentally uniting two claims to the throne and satisfying just about everyone.
Live Action TV
Rory Williams from Doctor Who. He loves his girlfriend, later fiancée, later wife, and will do anything to protect her. A lot of the time they protect each other- for example, Rory fails at sword-fighting a fish vampire, so Amy destroys it with a mirror. However he then goes to guard her comatose body for 2,000 years, becoming the legendary Last Centurion. He seems to develop something of a complex.
Rory: And she knows that where-ever she is, I am coming for her. Always.
Video Games
Despite providing the quote at the top, which suggests a 'It Gets Complicated' situation, Squall of Final Fantasy VIII really DOES get it easy. In order to protect Rinoa, the girl who finally brought him out of his sarcastic, just-dont-care shell, and taught him what love was - all he has to do is beat up all the villains. Then everything is all right.
Devil May Cry 4 provides another fairly straightforward (and heartwarming) example with Nero's half of the story with his Love Interest Kyrie. Though for a while it looks like he failed.
Gungrave. The protagonist's major goals is to get revenge on the main villain, and to protect the daughter of his former love interest from the main villain. By using a lot of dakka.
Fire Emblem 7: Dorcas's wife Natalie is an Ill Girl. He wants her to get better, and so he joins a bandit group. Once Lyn knocks sense into him (and Natalie does too, if you make them talk), Dorcas decides to keep fighting for her until he gathers enough gold to buy the medicine. It's just as simple as that, for him.
In Little Busters, Kyousuke feels this way towards Riki and Rin, and tries to encourage Riki to develop it towards Rin. In one of the final Bad Ends, when all of their other friends have died, Riki quietly promises to Rin that he will always protect her. She asks if he's proposing, and the player is given a choice whether to agree or not.
Western Animation
Adventure Time has Simon Petrikov, AKA The Ice King, protecting a very young Marceline either during or immediately after the Mushroom War. The fact that it's just been revealed means that the situation surrounding this could change, but so far it seems to be that he simply chose to look after her because she was scared and alone.
