Great Teacher Onizuka features this relationship with Tsundere Anko Uehara and Noboru Yoshikawa (who plays the role of Understanding Boyfriend). You NEVER mess with Noboru in Anko's presence unless you want a thorough beating. Kinda ironic when you consider the fact Uehara actually started out as a Loving Bully to Noboru.
Black Lagoon: As far as Revy is concerned, harming Rock in any manner is punishable by a disproportionate beat down for a first offense, and a bullet for a second (or even for a first if it's severe enough). When Chaka wants to goad her into a gunfight, he does so by wantonly beating Rock — and, later on, he gets what he had coming for it, as Revy trashes him for a bit and then leaves him at the mercy of his other victim's bodyguard: Ginji Matsuzaki, who is quick to give him a particularly horrible Cruel and Unusual Death for the shit he pulled on his charge, Yakuza Princess Yukio.
Similarly, her fellow "Vampire Princess" Yui was most pissed when the first Shinma she fought impaled her own companion Nagi with a spear. Notice that at such a particular point, Yui had just become a vampire and had next to no idea of how to use her newfound vampire skills — she fought anyway and used both guile and raw power to win
Kagome blasts Naraku apart just because he made fun of Inuyasha. She threatens the Peachman so much so that even Miroku and Shippou are amazed. Plus she blasts Kikyou's souls out of her TWICE for trying to kill him while she was in her Yandere days. She even shoots at Sesshoumaru and threatens him twice. Where would Inuyasha be without his girlfriend to protect him?
Once Inuyasha's revived ex-girlfriend Kikyou loses a part of her rage at the world and sets into Anti Heroine territory, she also threatens the evil priestess Tsubaki and openly warns her not to kill him. To put it on perspective: post-Yandere-phase Kikyou is a very serious Dark Magical Girl who almost always keeps what remains of her muddled emotionsin check and rarely if ever shows open anger... but the moment her old Rival Turned Evil tells her that she's gonna kill Inuyasha, she fires two arrows at Tsubaki (pining her robe sleeve to the wooden door), walks up to her and pulls on her hair while delivering her warning about Inuyasha. Seriously, don't mess with Kikyou.
Don't threaten (or even speak ill of) Keiichi from Ah! My Goddess lest you incur the wrath of his Goddess girlfriend. Several characters comment that Belldandy is terrifying when something threatens (or demeans) her boyfriend and the art work depicts her as looking unusually threatening (for her) when this happens. This was seen as early as in Urd's introductory episode, where Bell was pissed at her older sister for meddling with their relationship.
Diane from the series Nanatsu No Taizai might not be Meliodas' girlfriend but she will beat the living hell out of you if you try to hurt him.
In the original series, Anzu was very protective of Yugi ever since they were kids. While she's not an Action Girl or a big duelist, she is a determined Plucky Girl who does what she can to support him, and will stand up for Yugi's sake if he needs it.
Akhenadin noticed that Kisara either wouldn't or couldn't summon her powerful Blue-Eyes White Dragon ka to protect herself, but when it comes to protecting Seto...
Mana and her ka, the Black/Dark Magician Girl, are this to Yami Yugi/Pharaoh Atem and Mahaad/Black/Dark Magician.
Aki Izayoi reminds Jack Atlas of this trope when Yusei Fudo is kidnapped on Yu-Gi-Oh! 5Ds.
Juvia. Threatening Gray in her presence pushes her Berserk Button that scares even Erza!
Speaking of Erza, Erza herself became an example of this trope while trying to defend Jellal from both Midnight and Kagura.
If you find yourself in one of the Tenchi Muyo! universes, it doesn't matter which one; don't threaten Tenchi while Ryoko is around. Just don't. For that matter, Princess Ayeka will also be pretty pissed off at you.
Elizabeth "Lizzie" Middleford in the Black Butler manga decides to stop hiding her Lady of War side when she and her fiance Ciel were rodeated by zombies and he was unable to protect her. When this took place, the girl tearfully and fearlessly jumped to the guy's defense with two rapiers in hand...
(paraphrased) "I will become the wife of The Queen's Watchdog! BACK OFF HIM!"
Rosario + Vampire: If you ever hurt Tsukune, Moka will make sure you know your place. Unless Kurumu or Mizore beat her to it — if Tsukune himself doesn't kill you first, that is. Unusually for this trope, the one Tsukune truly wants as a girlfriend, Outer Moka, isn't really much use until her Rosary is removed and she becomesInner Moka, who will fight just as viciously as the others but does it for herself rather than for Tsukune ( at least at first).
Saori from Wandering Son acts this way toward Shuuichi, however they aren't dating and Shu apparently doesn't have romantic feelings toward Saori.
Rose of Versailles: While they're not an item yet, Oscar Francois de Jarjays completely flips her shit out when André Grandier is subjected to Eye Scream by Bernard aka the Black Knight, and very nearly kills the culprit.
In Ranma ˝, Akane becomes this whenever Ranma fails to properly defend himself against any real threat. If he's losing in a fight, she'll either help him kick your ass or she'll do it herself... or at least, she'll try to do it herself. It's not easy to defend your fiance when everyone else is better than you. Thankfully, her temper has made up for her lack of skills more than once. One time, she easily broke through thick bonds out of pure rage over someone threatening Ranma.
Akane: Let me go! If you hurt him, I swear that I'll...
Moon Phase: Once upon a time, a group of thugs roughed up Kohei Morioka, the favorite servant / blood donor / toy of vampire princess Hazuki. They were never seen again.
Both Usagi/Moon and Michiru/Neptune from Sailor Moon have put themselves at great risk to save their respective love interests, Mamoru/Tuxedo Kamen and Haruka/Uranus.
In episode 10 of Sword Art Online, a gloating Kuradeel kills one of his guildmates, then starts to torture Kirito, who soundly defeated him in an earlier duel. Were it not for the timely arrival of Asuna who had been following them, its likely Kuradeel would have also killed Kirito, then made up some random excuse as to why the two guildmates were dead to their guild leader Heathcliff.
Celty of Durarara!! develops this for Shinra after volume 8, after he is tortured almost to the point of death.
Anatolia Story: Yuri Suzuki. When the concubines who are butthurt because Kail is going the Ladykiller in Love way put scorpions in Yuri's bed in the same night that Kail was about to sleep in her bedroom, Yuri gets so absolutely pissed off that she storms into the room the girls are in and shouts that they can treat her as badly as they want, but they better not endanger Kail. She then correctly identifies the one who came up with that shit and throws the now-dead scorpions on her. And this isn't including the times she has ridden into battle to save him. She even gave up a final chance to return back to her home time in Japan to ride to Kail's rescue.
Haiyore! Nyarko-san: If you mess with her "Mahiro-san", Nyarko will turn you into a greasy stain on the pavement. In this case it's pretty well Justified, since it's literally her job to protect Mahiro and most of the things coming after him are horrible Eldritch Abominations from space that either want to kill him or do things like sell him into slavery.
In Kitsune no Yomeiri Ousuke, an unlucky everyman, ends up getting married to the kitsune princess Kyouka. Now, while she is a prankster and loves tricking her husband, with such things like drawing on his face as he sleeps, she does deeply care for him and his hard work ethic. When some thugs ruined all the potatoes he just finished peeling, she unleashed her fox fire on them.
Jyubee in Nejimaki Kagyu is sorta like this. She's a childhood friend to her teacher, Kamo, and wants to be his girlfriend once she finishes high school. But since Kamo is an unwitting Chick Magnet and the female student body at his school are literally crazy for him. She opts to protect him with the training she recieved while abroad in China. This isusually the result of anyone who threaten him or tries to separate the two.
The titular Human Aliens of Sekirei are this by default, being fiercely protective of their human partners. It's entirely justified, since killing the Ashikabi will terminate all their Sekirei and most Ashikabi are simply Puny Earthlings caught up in battles between superhuman Action Girls. The notable exception is Yukari Sahashi, who responds violently to anyone that dares to threaten her beloved Bishōnen, Shiina. Her tendency to hospitalize rival Ashikabi results in her becoming The Dreaded, while Submissive Badass Shiina winces in the background.
Pablo Francisco has speculated that this is the best part of having a Mexican girlfriend, because if you get in a fight, she will jump in and wipe the floor with the other guy.
X-23: You were dead the second you touched Julian Keller.
Susan Richards for Reed Richards, after she Took a Level in Badass and became the most powerful member of the Fantastic Four. (In fact, word to the wise: Don't threaten her son, her brother, or any of her friends either if you value your life.)
In American Vampire, Henry can usually take care of himself...but when he's outmatched, Pearl is more than willing to step up to the plate and deal with things. As Skinner Sweet, among others, found out the hard way.
Big Barda will destroy anyone who even looks at her husband Mister Miracle funny. That, or she'll teleport you to another galaxy...in the middle of space. Although, that's less her being a Violently Protective Girlfriend and more her being violent, period. Barda seems to believe all problems will go away if you beat them to an unrecognizable pulp. Which admittedly is accurate most of the time.
In the Uplifted series, Hanala'Jarva having several... incidents. Most of them justified. The last incident involving Hanala unloading a whole MP-40 clip into a starving runaway Jewish woman who was to be Joachim Hoch's sisters-in-law after he startles her into shooting him in the face. is more questionable.
In the Shamanic Princess fanfiction Divine Sorceress, Graham remains viciously protective of Tiara, but now, Tiara would be just as fierce in protecting him as well. When Graham got attacked by a Ryami, and advanced Mihan demon, an enraged Tiara switched to her demon form and struck at the Ryami without warning, and then she killed it.
In The Second Try Asuka is a Violently Protective Wife as well as a Mama Bear. Threatens Shinji or her daughter Aki and she will go on a rampage, like Zeruel, Kaworu and even Gendo found out the hard way.
In one continuum of Discworld fanfic, wizard Ponder Stibbons, the first to describe himself as weedy and ineffectual, ends up with a girlfriend who thinks the world of him. She is a sinewy, athletically graceful, hard as nails product of Filigree Street and her native Howondaland and she is prepared to deal a world of pain to anyone spoiling his day. In fact, she is a career Assassin. Ponder considers being with her is quite restful compared to the HEM and dealing with the Faculty. Ponder's love life with a trained killer may be found in the stories of A.A. Pessimal on Fan Fic.Net.
While the relationship is more one of Friends with Benefits - ie, sex without too much emotional commitment - Sally von Humpeding is this to Philip Holtack in Slipping Between Worlds. Philip is suitably thankful on both counts.
In The Wizard in the Shadows, Ginny is very much this trope, as those (very) few orcs and servants of evil who survived the Battle of the Black Gate can attest.
In Mass Effect, a female Shepard can show some signs of this trope, but in Weightless, it's turned Up to Eleven. To demonstrate, when Garrus had a clue to find Sidonis, he decided to go alone (as opposed to canon) so that Shepard would be safe. What did Shepard do? Used brute force on him (while they were naked and lying in his bed no less) and ordered Garrus to take her with him because it is her business to deal with the one who hurt what belonged to her (Garrus). Then she proceeded to kill everyone who stood in her way because they may be traced back to Garrus. Even Garrus found her decidedly Renegade behavior a bit unsettling and compared her to Aria.
While Jack isn't her boyfriend (at this point in the story) in the Rise of the Guardians fic Guardian of Light, Helen still shows this towards him and almost kills her own father when said father almost kills Jack.
In the Star Trek fic Safe and Sound Khan's augment lover Victoria once saved him from thirty armed guards during the Eugenics Wars by killing them with her bare hands. Khan admits this was when he fell in love with her.
Avatar: Neytiri is vividly protective of Jake, crouching over him with knife drawn and teeth bared, hissing, in two scenes where he is unconscious and under threat. And when Quaritch is about to kill Jake, she puts two arrows into his chest.
Uhura in Star Trek Into Darkness when Spock is about to be killed by John Harrison, she immediately beams into the fight and blasts Harrison with her phaser multiple times, buying enough time for Spock to regain the upper hand.
Trinity from The Matrix will not hesitate to end you if you hurt Neo.
Underworld: Hurting or killing Michael will result in Selene decapitating you or having your body ripped to shreds.
In Indiana Jones and the Kingdom of the Crystal Skull Indy tells Mutt to punch a college student wearing a letterman jacket to escape two armed KGB agents at a malt shop. His girlfriend yells "Hey! That's my boyfriend!" and punches Mutt causing a big fight between jocks and greasers.
Scott Pilgrim vs. The World: Ramona to Roxy when she knocks her down for attacking Scott: "Do that again, and I will END you!" Cue the catfight.
The Iron Man franchise has Pepper Potts; Tony Stark's secretary who eventually becomes his girlfriend. She's sweet, she's professional, she gets things done, and most of the time she's keeping Tony from doing stupid things. In the third movie, she ends up injected with the Extremis virus by the main villain, who hopes to keep her as a trophy to get back at Tony. As you can imagine, this ends badly for the villain when he threatens Tony, and ends up being taken down by an angry, super-powered Pepper with a combination of her new powers and Tony's armour. Let's just say the villain won't be bothering anyone again.
Speaking of the Marvel Cinematic Universe, Bruce Banner's girlfriend Betty has a moment of this when she gets angry at a taxi driver for almost causing Bruce to Hulk out. She's not exactly pleasant when Bruce tells her to calm down.
Betty: (kicks taxi door shut, causing the driver to put his foot down pretty fast) ASSHOLE!
Sally Kimball of Encyclopedia Brown fame. Not quite played straight, however; Encyclopedia paid Sally to be his bodyguard. To what extent her affections eventually became engaged is less clear, and there is at least one mystery in which she defends another guy against Encyclopedia's (correct) accusations, although not physically.
Explicitly used in the Shield, Sword, and Crown series, where Arisa declares herself both Weasel's and Edoran's bodyguard at various points in the book. Slightly subverted in that she isn't interested in them romantically at all, and thinks of them as best friends.
In the third book of The Immortals, Daine believes Numair has been executed by the Carthakis and proceeds to go on a rampage, reanimating a bunch of dinosaur skeletons, and razing the entire Imperial Palace. When confronted later, she says "I thought you were dead. I lost my temper."
Lord Byron's explanation in his Don Juan for why a Woman Scorned is more dangerous than a Mama Bear could also apply to a Violently Protective Girlfriend:
For what is stealing young ones, few or many, To cutting short their hopes of having any?
Una and Britomart of The Faerie Queene won't let anyone harm their fiance, the Knight of the Red Cross and Artegall.
Lisbeth Salander of The Millennium Trilogy is more of a Violently Protective Sexbuddy, but all the same, do not harm Mikael Blomkvist when she's nearby.
When she found out who hired the killer that attacked her boyfriend, Honor Harrington dueled both the killer and his sponsor with pistols.
A later lover of hers offers the Genre Savvy observation that if they were ever attacked, he'd hold her coat while she dealt with the problem.
While Carrot is no weakling, standing over 6ft and extremely strong, his girlfriend Angua (a werewolf) is very protective of him nonetheless, sensing on an instinctual level when he is injured or in danger.
This is a classic Pratchett gambit: the weakly ineffectual male who acquires a tough and protective girlfriend. Nerdy Nijel, the would-be hero, ends up with killer hairdresser Conina fighting for his life.
Rincewind, who at one point had Conina's favor, is similarly body-guarded by the ninja-trained Pretty Butterfly
Even functioning males such as Moist von Lipwig benefit: Adora Belle Dearheart wins a fight for him in the Mended Drum, sending a bully away whimpering by driving her high heel's point into the man's foot with clearly telling him how easy it would be to push it all the way through his foot. As the bully would otherwise have ripped Moist's head off, and Adora Belle knew this, Moist is only too thankful, but takes note of what he has just witnessed.
In Swedish fantasy novel Spiran och staven (The Sceptre and the Quarterstaff) Fox's overweight girlfriend Livneth turns out to be a cold-blooded and very skilled knife-wielder when Fox is threatened by a gang of hoods. The fact that Livneth originally belonged to a tribe of forest barbarians might have something to do with it.
Rachel in Animorphs. When Tobias is tortured by Taylor, Rachel is ready to literally rip her to pieces in grizzly morph, and it's only Tobias's pleading that stops her.
Angelina, in Harry Harrison's Stainless Steel Rat series: began as somewhat yandere for Slippery Jim di Griz, her personality integrated more after marrying him. But let anyone dare approach Jim with violence in mind when Angelina is nearby...
Karrin Murphy may not necessarily be Harry's girlfriend (yet), but the lengths she will go to to protect him are unbelievable. Standing over his incapacitated form and shooting MacGuffin .22 calibre bullets at a half-ton of demon werewolf is only one of the many instances of this. In another, a chainsaw is involved. And in Cold Days, Karrin says specifically "If you're going to Hell and back, I'll be there by your side the entire way." in a Crowning Moment Of Heartwarming. In this book, this violence was taken into a gambit because Mab knew of Karrin's feelings and knew she likely had back-up weapons on her. So when Maeve was about to kill Harry in front of Karrin, the woman didn't think. Karrin just reacted on instinct and shot Maeve in the head with a small back-up from her ankle holster.
The full extent of Lily and Fix's relationship isn't said, but with this Lady and Knight pair, harm him and she will send waves of fire at perpetrator, or even just a tiny star-like attack that melted a Sidhe-made blade.
The Princess Ren and her sisters in A Brother's Price when their husband Jerin is kidnapped, though it's seen as rather normal in that world - men are rare, protected, seen as more tender, and commonly abducted and raped by women despite that being illegal. Entire families of sisters and mothers are expected to be violently protective in order to protect their menfolk, and the princesses think that wiping out the entire family of Jerin's abductor(s) is a totally reasonable response to this offense.
Arguably Katniss for Peeta in Catching Fire. She is more than ready to kill anyone who tries to harm him. Still arguable though since their relationship is mostly for show... mostly.
Aricella Santos in part two of the two-part season finale of Law & Order season 9. When NYPD Detectives Leonard Briscoe (Jerry Orbach) and Reynaldo Curtis (Benjamin Bratt) try to arrest Santos' boyfriend Leo Zamora for the murders of Tony Ricci and another woman, as well as the attempted murder of the second woman's ten-year-old son, after a visitor to the building where Miss Ricci was murdered identifies Zamora, Zamora takes off with Briscoe and Curtis chasing him on foot. Zamora runs into a building where Briscoe and Curtis finally catch Zamora, but not before Zamora calls out for Santos. As Briscoe is cuffing Zamora, he sees Santos charging down the stairs at Curtis with a knife in her hand and warns him. Curtis knocks the knife from her hand and pulls his Glock semi-automatic pistol, which makes that hammer-cocking sound despite not even having a hammer to cock in the first place, and Curtis threatens Santos with death if she moves. It turns out that Zamora and Santos are wanted for a murder in Florida and that the Russian mobstershired Zamora and Santos to kill the ten-year-old because he was a witness the ruthless mobsters didn't know about till trial, his mother, and Miss Ricci.
Fiona from Burn Notice. And she's a Trigger Happy ex-terrorist, so when she gets pissed off things explode. This comes back to bite her, when a psychiatrist uses that knowledge to frame her for murder by causing her to explode Michael's ex-mentor.
You might think that a crime lord would be immune from this trope, but no. Season I of NYPD Blue had Janice Licalsi, a corrupt New York Cop who just happened to fall in love with honest cop John Kelly. When mafia boss Angelo Marino (whose pad she's on) demands that she kill Kelly, Licalsi cold-bloodedly murders Marino and his driver.
Willow Rosenberg, with regards to Tara. When Glory drove Tara insane, she only survived her battle with Willow because she was a Physical God. When Warren killed Tara, Willow flayed him alive.
Also doubles as a violently protective BFF. She threatens death on anyone who hurts Buffy.
Tara gets her moment too. Even though her skills are on the research and magic side, so she otherwise never gets physically involved in battles, when Willow is threatened? Lack of weapons training is irrelevant, she's getting a one-blow instant kill with an axe.
Buffy herself was like this with regards to Angel.
Amy Pond. Any time someone hurts her boyfriend Rory, she will end them. In one, she incinerates an alien fish disguised as a vampire. In another (which was all a dream), when Rory is hurt by a bunch of aliens disguised as old people, it creates the surreal image of Amy (at the end of a very large pregnancy) mowing down a group of elderly citizens in a van.
The other way around is also true. The normally timid Rory can go berserk if something happens to Amy. Of course, he's had 2000 years of experience as an Auton/Roman legionnaire.
Rose. Hurt the Doctor (or Jack) and she will ascend to being a Physical God and obliterate you with the raw power of time itself.
Leela tops the list for Violently Protective Companion, being originally a member of a primitive warrior tribe. The Doctor had to routinely keep her from killing everything that got in their way.
Barbara Wright from the very beginning ended up marrying her fellow travel companion Ian. Before that, she held a higher headcount than the other protagonists combined and at one point mowed down a group of Daleks with a lorry. Note that Barbara was a history teacher.
Dana Scully does not take kindly to anyone hurting her partner. She may be petite, but she's smart as a whip and has great aim. In "Beyond the Sea", after Mulder is shot:
Scully: This was a trap for Mulder because he helped put you away. Well, I came here to tell you that if he dies because of what you've done, four days from now, no-one will be able to stop me from being the one that will throw the switch and gas you out of this life for good, you son of a bitch!
The episode "Biogenesis" and the entire "Sixth Extinction" arc was pretty much Scully kicking ass because the Cigarette Smoking Man and Diana Fowley had caused Mulder's fatally unusual brain activity. The same happens in Season 8, despite the fact that she's pregnant at the time. And this totally works in reverse, as well. As noted on that page, Mulder and Scully are each other's Berserk Button.
The second movie has her bashing bad guys over the head with firewood to get to Mulder.
Sarah from Chuck. While she isn't exactly Chuck's girlfriend ("it's complicated"), at least not in the first two seasons, she tends to get displeased when someone threatens or actually tries to hurt him.
Just ask Michael Clarke Duncan. After he dropped Chuck off the roof of a high-rise, Sarah got understandably pissed, and the only reason he survived is because he's built like a tank.
She actually murders a man in cold blood after disarming him, after he made the mistake of taunting her that he knows that Chuck is the Intersect and will tell his bosses. Chuck witnesses the murder, which doesn't make things better between them.
She becomes all the more dangerous (and this is saying a lot) after she and Chuck became the Official Couple. The writers turned this Up to Eleven in Chuck vs. Phase Three when Sarah tears apart Thailand looking for a kidnapped Chuck. Everyone from the lowest mook to the episode's Big Bad was scared shitless of the "Giant Blonde She-Male."
The Fresh Prince of Bel-Air had this. Will starts dating a girl and brings her to a bowling alley, where they're harassed by some meat-head trying to woo her away. He knocks out Will with one punch, but then gets BODY-SLAMMED by the petite woman. When Will gets up and realizes what happened...
Girl: I'm sorry, Wil. I meant to tell you, I... I'm a—
Do not ever harm, or threaten to harm, Wash in front of Zoe. Not if you want to live.
More of a violently protective little sister, but basically the same thing goes for River and Simon. River will end you. Just ask the Reavers.
Lily is like this towards Marshall in How I Met Your Mother, once even delivering a No-Holds-Barred Beatdown to a woman who forcibly kissed Marshall when she was drunk. It's rather hilarious though, because Marshall is burly, 6'4'', and a practiced fighter, while Lily is about a third of his size, small-boned, and very girly.
Parker on Leverage occasionally gets this way with Hardison. In the Grave Danger Job she draws fire from an Uzi and during the Experimental Job she delivers a No-Holds-Barred Beatdown against the members of the secret society that had captured Hardison
In Friends Monica has shades of this concerning Chandler. Notable in this exchange when they're having photos taken.
Monica: "Chandler, what is wrong with your face? Its meant to say Geller and Bing to be married, not local woman saves drowning moron!"
Monica: "DON'T LAUGH AT HIM! He's my drowning moron!"
On another occasion she and Chandler were arguing with their neighbour Janine; things were pretty aggressive before but its when Janine insults Chandler that Monica cracks and gets physically violent.
Janine: [to Chandler] "You know, I know you’re talking, but all I hear is, "Blah. Blah. Blah-blah-blah."
Monica: "All right, you and me! Let’s go! Right now!"
Aeryn to John on Farscape. Once he takes his badass levels he's perfectly capable of fending for himself (and saves her ass plenty of times), but you do not mess with John and get away with it, at any stage of their relationship.
Aeryn:(while holding two women by their necks up against a mirror) Now listen to me closely so that there's no misunderstanding. I don't know what game's being played on this little planet of yours, and I don't really care. What I care about is that a good friend of mine is not hurt — in any sense of the word. And if he is, I will personally take revenge on both of your overly made-up faces.
Lindsay Messer on CSI NY fits into this-it was both her husband and child being threatened by Shane Casey, but she did shoot him. And probably would get physical again if she had to, considering the verbal confrontation with the rookie cop who lied and tried to get Danny in trouble to protect herself. No blows were exchanged, but it's obvious she'd go there again if it came to it.
Temperance Brennan on Bones. Though Booth usually stands up for her, even though she can handle herself, there's little reason to doubt she'd fight to save him. She might even have once or twice, hard to recall.
Two occasion confirm this. In "The Wannabe in the Weeds", when a psycho stalker aims a gun at Brennan, Booth takes the bullet for her. Brennan's response is to, in one fluid motion, grab Booth's gun and shoot the stalker dead. And in "The Hero in the Hold", when they confirm that Heather Taffet is the Gravedigger, a serial killer who had trapped Booth on a Naval vessel slated for demolition, before rushing to Booth's rescue, Brennan whacks her upside the head with a metal briefcase, hard enough to knock over her and the chair to which she is handcuffed.
Babylon 5: Ambassador Delenn doesn't get involved in dust-ups most of the time to keep John Sheridan safe. She doesn't have to. She's got an entire space navy of Cool Starships at her command, and she is not afraid to use them. However, when she does get into more personal fighting, that willowy, ladylike Minbari can proceed to kick ass with the rest of them. Don't hurt her boyfriend. Ever.
"Why not? Only one human captain has ever survived battle with a Minbari fleet. He is behind me. You are in front of me. If you value your lives, be somewhere else."
Carla has hints of this towards Turk in Scrubs, at one point Turk has to physically pick her up and carry her off to stop her from beating up a fellow surgeon who was mocking him. She's also a Spicy Latina, for extra points.
Deconstructed in an episode of Saved by the Bell. Zack dates a female wrestler who saves him from an attack. He views this as a huge blow to his ego because he can't comprehend the girl saving the guy.
As seen on Castle, do not attempt to harm Castle, because Beckett will hurt you.
Although not really dating, Ziva fits this for her partner Tony in NCIS. The most obvious example comes in season 6's "Cloak" when Tony and Ziva break into a secure facility. When they are found out, they're approached by military security, but ordered (by Gibbs) not to engage. On a reflex, Ziva throws the first punch, while Tony rapidly tries to defuse the situation so neither of them get shot. It doesn't work, and Tony gets a rifle butt to the head for his trouble. As soon as Tony goes down, Ziva loses it. She plows her way through the soldiers like paper, and it takes three of them to take her down. As soon as she awakes, the first words out of her mouth are: "Where's Tony?"
In Everybody Loves Raymond, Debra Barone intervenes when Ray is getting the worst of it from Peggy The Cookie Nazi. The scary Peggy backs down quickly, recognizing an even more powerful force of nature, while a floored Ray looks on admiringly.
In the version of the folk song Stagger Lee recorded by The Grateful Dead, Stagger Lee murders Billy DeLion, and the police are too afraid of him to do anything about it. Then, along comes Billy's girlfriend Delia, who shoots Stagger Lee herself. In the balls.
Tijuana Sweetheart's single "Seven" (from back when they were called Vagiant) is all about this trope, as quoted on the quotes page.
Odin Sphere: Although she didn't like Oswald at first, Gwendolyn shows that she is capable of wreaking all sorts of havoc when he's in danger. One of the game's major Nice Job Breaking It, Hero incidents revolves around this trope.
Liara apparently subscribes to this trope. After Shepard was killed at the start of the second game and spent two years in a coma, she went on a one-woman crusade to recover the Commander's body from both the Shadow Broker and even the Collectors. She then went on a two year quest for revenge on the Shadow Broker (one of the most powerful individuals in the galaxy) for even THINKING about causing harm to him/her.
Ashley Williams also skirts this line during the first game, if you're unable to prevent Wrex from his Face-Heel Turn, she will kill him to prevent him from harming Shepard.
A female Shepard can become this depending on the player.
Even more so if you romanced Thane back in Mass Effect 2. Watching her gut his killer, Kai Leng, like a fish with her omniblade is very, very satisfying.
Shepard:That was for Thane, you son of a bitch!
And if a female Shepard is romancing Liara, when she's talking to her "father", she echoes an earlier line when the possibility of an assassination on Liara comes up.
Shepard:Nobody messes with my girl!
Tali also gets hints of this in the third game. When you find clips of the Illusive Man casually discussing the best ways to emotionally manipulate Shepard, what is her very calm response?
Tali: He needs to die.
A more disturbing example shows up in a sidequest in the first game. Shepard is called to investigate an abandoned ship. It turns out that one of the crew members, a female biotic, flipped out and killed the crew when they attempted to shut off her comatose boyfriend's life support after determining he was brain-dead.
A male example in Garrus Vakarian if romanced by a female Shepard. While downplayed on the violence angle, he does upgrade Shepard's apartment via explosive gas, a weaponized coffee machine, cyanide-filled kitchen sinks, and a hot tub heated to solar temperatures. Admittedly, this also happens in playthroughs where you don't romance him - Garrus is apparently itching, deep-down, to overhaul an apartment into a trap-encrusted no-man's-land - but if there is a romance taking place, you get variant dialogue where Garrus begs you to indulge your crazy boyfriend and let him continue attaching microfilament explosives to your decor.
Garrus: Nobody better hurt you, is all I'm saying.
Bobcat in City of Heroes. In Issue 19, there's a task force that finishes with a battle between your team, and her and Neuron. Defeating Neuron before taking her down to half her health, and defeating her, gets a badge. The badge says "You saw Bobcat do something no one else has seen; fight with all her effort. Despite her best efforts, you still managed to put her down."
In Kingdom Hearts II, Kairi's only fight scene thus far in the series was in response to seeing Sora get ambushed by Heartless, drawing them to her so that they'll leave Sora alone.
Senran Kagura plays this for laugh as the normally-quiet Yagyū shows no hesitation in uttering death threats at Katsuragi when the latter tries to grope Hibari; Katsuragi sees no reason to believe that she isn't being serious and quickly backs off.
In Star Wars: The Force Unleashed II, hurting or threatening Juno Eclipse is Starkiller's Berserk Button, but it works in reverse as well. When Darth Vader tries to turn Starkiller to the Dark Side, Juno grabs one of Starkiller's lightsabers and attacks Vader herself!
The character Aveline is introduced as her husband Wesley is disarmed by Darkspawn, upon which she blindsides it, punches it silly and cuts its head off, all the while proclaiming, "You will not have him! They will not have you, not while I breathe."
Female!Hawke has a moment like this if you're romancing Anders: you can tell him that, if the Templars come for him, they'll have to go through you first.
Marble in the erotic game Corruption Of Champions does not like it when others mess with the PC after she has been romanced.
Kerrigan: "If Jim is alive, no force in the Universe is gonna stop me from saving him."
Arcueid to Shiki Tohno from Tsukihime. The natural result when your love interest happens to be pretty much the most powerful thing on the whole freaking planet. Given how insanely scary and unstable Arc can be at times, its a real good thing that Shiki is more than capable of taking care of himself.
Ally: Listen hard, you cradle-rapin' fuck! Hit "Undo" or I'm shovin' bone splinters from y'r nose straight into y'r precious brain! Fitz: Technically it's not my nose. Ally: Y'think this is open-mike night, corpse? This ain't a bluff! You are not fighting an idealist now! She moves or I end you!"
In Homestuck, this seems to be a trend. Terezi, Latula, and Vriska have all at some point defended their boyfriends by telling another girl 'if you touch him, I will fucking kill you!' As troll society considers gender largely irrelevant, and considering how aggressive trolls are in general, this would probably be seen as normal.
Shortpacked! - NEVER threaten Leslie while Robin is around - even if you're functionally immortal. She'll just cut you up and throw your remains into different universes before you can regenerate.
Kira from Panthera embodies this trope, as one does when they work on a covert operations team with said boyfriend and can transform into a tiger at the drop of a hat.
Girl Genius: While the men in her life can usually take care of themselves, if things get to be too much for them, Agatha Heterodyne will. Take. Steps. And whatever was threatening her men will soon be very, very sorry...
Will and Cornelia are both this towards their respective boyfriends Matt and Caleb in W.I.T.C.H.
Flame Princess in Adventure Time as demonstrated in "Vault of Bones" when a giant Goo Skull made the mistake of capturing Finn.
Borderline case in My Little Pony: Friendship Is Magic, episode "Dragon Quest": the ordinarily fussy and prim fashionista Rarity threatens to beat up a bunch of dragons if they so much as hurt a scale on her "Spikey-Wikey". (They're not a couple, but he's had a crush on her since they first met, and she knows about it.) Note that although Rarity is outclassed this time and forced to beat a retreat, she has faced off against multiple deadly threats in the past.
George Harrison's wife Olivia saved him from being murdered by an insane intruder in 1999. When said intruder broke into their home, George initially went out to confront him in the hopes of diverting attention away from his wife. He was stabbed repeatedly in the process, at which point Olivia came out and beat the hell out of the fifteen-years-younger intruder with a fireplace poker, successfully disabling him.
Watch an episode of COPS sometime. Even if the woman is calling to report her boyfriend/husband is abusing her, if they attempt to arrest the boyfriend, often the woman will turn her rage against the cop.
Henriette Caillaux: In pre World War One France, a big feud erupted between her husband Joseph — then the left-leaning minister of Finance and a proponent of progressive taxation — and the conservative newspaper Le Figaro. In order to destroy Joseph Caillaux's reputation, Gaston Calmette, the Figaro's director, bribed the Caillauxs' maid to steal embarrassing letters Joseph had written (get your minds out of the gutter; the letters indicated he had secretly sunk a Senate bill on taxation he publicly supported as a political tactic). Henriette did not approve: she made an appointment with Calmette, and once in his office, simply said, "You know why I am here," before shooting him five times in the chest.
Then, because simply killing someone who attacked her husband's reputation was not enough, she and her lawyer took advantage of the existing stereotypes of the time, pleaded the unpremeditated crime of passion despite the fact that premeditation was glaringly obvious, and eventually was acquitted a mere four months after the murder, before starting a career as an art historian while her husband stayed in politics until 1940.
During the Leveson Inquiry, a man broke into Parliament's chambers to throw a plate of shaving cream in Rupert Murdoch's face. His wife Wendi responded by lunging for the attacker and slamming him in the face with her palm.
It's awesome when wives/girlfriends fend off other men. It's even more awesome when a woman fights off a tiger.
Another similar story: an elderly couple were walking in the woods when the husband was attacked by a cougar. His wife beat the hell out of this mountain lion with a branch about as big as she was and stabbed it in the eye with a pen, causing it to leave her husband alone and flee. Investigators later found the cougar's battered carcass.
The Ukrainian woman Mariya Oktyabrskaya. When the Nazis killed her husband she sold everything she owned, bought a tank with the money, and then spent the next two years blowing up any Nazi she could find.