The Professional Killer is as deadly as he is serious about his job, "Nothing Personal, it's just business" is their favorite quip for a reason. He can spend months infiltrating a target's life and winning their confidence without hesitating to pull the trigger once the order comes. Of course, there's always that one target... not The One That Got Away, but the one that got into their heart.
Love has a way of sniping even the coldest heart, and against all sanity and better judgement the hitman grows a heart. Maybe in the process of casing the target he (usually a he) may discover she's just an Innocent Bystander who saw too much, and his Badass Creed emphatically says to Never Hurt an Innocent. Then again, it may just be plain old messy love sprouting as some ineffable quality of the target strikes a long dormant chord in his heart. Maybe they just have really good sex.
At first he'll make increasingly implausible excuses to his superiors at the assassin's guild to justify not killing his Love Interest, even protecting her from rival hitmen until ultimately they decide he's gone rogue and put a Contract on the Hitman. Interestingly, whenever this happens the hitman was usually going to be betrayed anyway either by the client or his organization, and the defection quite literally saves his life.
The former target Love Interest will of course be really freaked out once she finds out the man she loves wanted to kill her not days ago, but usually rolls with it surprisingly well and trusts the hitman with her life implicitly. A weird sort of Stockholm Syndrome can be said to affect both: though their love is genuine, the situation is eerily similar. The old assassin's maxim "Don't get involved with the mark, it can get messy" is putting it mildly.
Another dilemma facing the Hitman with a Heart is just what exactly to do vis-a-vis his former colleagues and innocents. Now that he's essentially done a Gender Flipped High-Heel–Face Turn into at least being an Anti-Hero, he can't just kill anyone he pleases. The Love Interest usually insists on holding him to a more moral standard, and only killing those who attack them or betrayed them.
Not to be confused with being in love with someone named Mark.
- Akuma no Riddle is a manga series about a class in which twelve assassins target a normal girl named Haru Ichinose. One of the assassins, Tokaku Azuma, falls for Haru and eventually decides to protect her from the other assassins.
- In Attack on Titan, Ymir hints that she befriended Krista with the sole intention of using her to convince the enemy to pardon her past crimes. Instead, this is what happens.
- City Hunter's character Mick Angel plays with this. Whenever the mark has a girlfriend of woman, he seduces her before completing the job, allegedly to make her suffer less (given the first we see of him is seducing a woman who is about to marry and whose fiancee is not his mark, this claim of his is somewhat doubtful). Then Union Teope sets him on Ryo, so he goes to seduce Kaori... Only to actually fall for her.
- Rolo in Code Geass develops a strong, genuine, but also horribly twisted affection for Lelouch Lamperouge while posing as his younger brother to monitor him and saves his ass (which kills him).
- Crying Freeman is kickstarted by this trope: Emu Hino saw Yoh Hinomura for the first time right after he murdered one of his targets, so she was singled out for death... but she and Yoh fell in love and ran away together, thanks to Emu convincing Yoh to make love to her so she would not die a virgin.
- El Cazador de la Bruja has an episode where Nadie and Elis meet a husband and wife running a restaurant. Turns out that the husband was originally hired to kill the woman, but fell in love with and married her instead.
- Irresponsible Captain Tylor: Harumi was originally sent as a spy by the Raalgon Empire to infiltrate the Soyokaze, and eventually given the order to murder Tylor by her superiors. However, spending time with him causes her to fall for him. Even more impressive when it turns out she's actually an android, and shouldn't have even developed feelings at all.
- In Nisekoi, the hitwoman Tsugumi develops feelings for Raku.
- One episode of Noir has Kirika befriending a target. She kills him anyway.
- Princess Connect! Re:Dive: While the assassination part is downgraded after one attempt, Karyl ends up sucked into Pecorine's found family after joining the group to spy on her, also getting a lot of Ship Tease.
- In Risky☆Safety, the oni woman Kade was sent to assassinate one of the Momotaro men. He sensed her attack, blocked it...and then they saw each others' faces and fell in love. Much to their respective armies' dismay.
- Ironically played with in Rurouni Kenshin. Assassin Kenshin and Tomoe fall in love with each other. However, the mark is Kenshin, not Tomoe, who is a spy for Kenshin's enemies, who intended to invoke this trope on purpose in order to use her as a hostage and lure Kenshin into a trap. Poor Tomoe tried to help Kenshin break through, and got killed (and by a blinded Kenshin, himself) for her trouble.
- Sheila begins travelling with Exa under the pretense of waiting for the right opportunity to kill him, and often notes that she will have to kill him someday before he can find out she's the Demon Queen, but can never quite bring herself to do it.
- Exa is also an unwitting example of this, as he falls in love with Sheila without knowing that she is the Demon Queen- the one he is on a quest to defeat, and the one being he is willing to kill.
- In To Love Ru, the Living Weapon Golden Darkness was initially hired to kill Yuuki Rito by Lacospo (one of Lala's suitors). After learning that Rito is not Lacospo described him to be, she turned on him, but still claims that she will kill Rito eventually and will stay on earth until her mission complete (even though the job is technically over). In the sequel To Love-Ru Darkness she ends up falling in love with him. So much so that her "Darkness" mode (when is actived the first time)) wants to kill him so that he can live on forever in her heart.
- Tsukiyama is believed to develop feelings towards Kaneki in Tokyo Ghoul besides just seeing him as a meal.
- Rethink your definition of "love", and you have Seishirou Sakurazuka from Tokyo Babylon and X/1999.
- Zoids: Chaotic Century has a parental (of sorts) version. Rosso and Viola are a pair of mercenaries hired by Proitzen to kidnap and kill Prince Rudolph so he can take over the Guylos Empire. They end up bonding with the boy, to the point they pull a Heroic Sacrifice to help him escape with Van from Raven. Later it turns out they survived, and become his official bodyguards.
- Aquaman: This was added to Mera's backstory in Brightest Day, which eventually bled over into the New 52. Here, she was the princess of the former penal colony of Atlantis, Xebel, and was originally sent to kill Arthur. However, she fell in love with him and opted to stay with him and marry him, keeping her past hidden until the events of Brightest Day.
- Death Vigil: The necromancer in the first issue genuinely fell in love with Clara at some point before he tried to sacrifice her to evil entities that want to eat reality.
- Judge Dredd: Played for laughs in a non-canonical strip. A woman introduces her ex to her new beau, who happens to be the undead superfiend Judge Death. Apparently they met while he was busy massacring a club full of hundreds of people before a Meet Cute.
- Spider-Man: Probably the case with Yith, a snake-woman assassin hired to kill Curt Connors in the mini-series Spider Man: Quality of Life. Yith had been paid by Clifton Arliss to get rid of Connors (who had discovered the dangerous health risks of his agricultural projects), but started feeling sympathy for him after hearing about the death of his wife. Eventually, during a fight between Spider-Man and Curt (who had become the Lizard) she did little but watch, and after passing up several easy shots at Curt, she pointed her gun at her employer and asked if he'd ever been in love before - then let him have it. (And then left without an explanation.)
- Against her better judgement, what ends up happening to Thirteen towards the titular character of Scissor Seven, Seven. Even when she tried to kill him twice (which he didn't really mind). Her master, Green Pheonix, ackowledges this and warns her via an ultimatum: Give up on Seven and leave him to his fate, or take his side but not being an assassin anymore. After attempting to go for the former, she finds herself unable to do so, and takes Seven's side, saving his life.
- About Life, a Rule 63 fanfic, has this as the origin of Anakin and Padmè's relationship. The Sith assassin Darth Vader was originally sent to kill Padmè to stop his efforts at promoting peace and diplomacy between the Republic and Confederacy, but when she infiltrates his quarters she instead becomes infatuated with him.
- The Guy Who Cried Grendel: This happens to Benedicta, a Khornate cultist. She originally impersonated a Sister of Battle in order to get close to Grendel so she could find out why he kept defeating powerful daemons and possibly kill him herself. Then he saved her from an explosion, causing her to fall for him.
- In the infamous Warhammer 40,000 fanfic Love Can Bloom the Vindicare Assassin LIIVI, despatched to finish off the defeated Eldar Farseer Taldeer, hesitated when he watched her take off her Ghosthelm to reveal her face through the scope of his rifle and fell in love with her (despite not knowing why). He goes rogue to try and save her, despite the history of enmity between their races and the Fantastic Racism that heavily pervades both Elder and Human culture.
- My Mirror, Sword and Shield: Suzaku is a time traveler who only made himself close to Lelouch to ensure that his timeline isn’t wiped out by Lelouch dying too early or too late with plans to assassinate him himself as insurance. Suzaku ends up falling in love with him and begins to lose his nerve. He ends up faking Lelouch’s assassination and saves him by taking him to Suzaku’s future.
- Whirlpools Among The Eddies: Karin was largely supposed to lure Naruto out of the village to be captured by Orochimaru and Kabuto, which she was sure would end up with him wishing he was dead. The month spent getting him ready for the Finals left her falling in love with him, despite knowing the consequences of failure, and thus betraying them.
- Wilted: Mercury Black is instructed to befriend Team RWBY, and Ruby Rose in paticular, to make sure she doesn't suspect Team CMSN of being the infiltrators; it goes an unexpected direction when the two begin dating, turning Ruby into a Morality Pet for Mercury, and causing a crisis of loyalty. By the time of the finals round of the Vytal Tournament, Mercury, as well as Neo and Roman, have cut a deal with Ozpin to help them stop Cinder in exchange for his protection.
- In Hercules, Hades ordered Meg to spy on Hercules to find out if he had a weakness. Meg and Hercules end up falling in love. Hades is initially furious, but then he gets wise to how he can take advantage of this...
Meg: Besides, O Oneness, you can't beat him. He has no weaknesses! He's gonna...
Hades: I think he does, Meg. I truly think he does.
- In The Road to El Dorado, Miguel starts to fall in love with lifestyle he is living by pretending to be a god, while Tulio falls in love with Chel, the native girl helping them pull of their con. This causes to tension between the two of them, as each thinks the other is losing sight of the original plan, and leads to this exchange:
Miguel: Hey, it was his stupid plan!
Tulio: My plan was that we should lie low! But your plan was to run off and be all "Oh, look at me, look at me, I'm a God!"
Miguel: That's not true!
Tulio: No? Who are you kidding?! You're buying your own con!
Miguel: At least I'm not dating mine!
- Ćon Flux. It's a Justified Trope because they were lovers in a past life.
- Bulworth: The titular senator ordered his own assassination, but when the assassin realizes the progressive influence Bulworth could bring, she decides not to fulfill the contract. Sadly, that doesn't stop someone else from killing the senator.
- This occurs off-camera in the movie Conspiracy Theory.
- Drive a Crooked Road: Not love exactly, but Barbara does develop feelings for Eddie, the poor sap she is manipulating into become the Getaway Driver for her gang. As she gets to know him, she realises that he has never known love in his life before, and that not only will her plan turn him into a criminal, but finding out that she never loved him will destroy him psychologically and emotionally. She gets cold feet and tries to persuade her partners to find someone else, but they refuse.
- Played with in Grosse Pointe Blank. The hitman is actually in love with his mark's daughter.
- This is the core plot of The Handmaiden. Sook-hee begins falling for Hideko almost immediately upon meeting her, stunned at her beauty. It is a mutual trope, considering that Sook-hee is the real mark of Hideko and Fujiwara's con, and Hideko falls in love with Sook-hee, too. This leads both women to confess their respective con plans to one another and making an new plan to fool Fujiwara.
- It's revealed in the Spanish film The Honeymoon that Jorge was hired to kill Isabel by her fiance but instead fell for her, kidnapped her and forced her to be his "wife".
- A bromance version occurs between Dave Skylark and Kim Jong-un in The Interview. Of course, Kim is just "honeydicking" Dave.
- Killer Angels: The relationship between Special Force Agent Yau-li, and triad hitman Michael; when he is assigned to kill her, he ends up having feelings for her instead.
- The Hong Kong movies Killer's Romance and Dragon from Russia are both based on Crying Freeman above. Killer's Romance gets straight to the action and is a fairly loose adaptation of the manga/anime, while Dragon From Russia has a fairly involved origin story for their version of the Freeman and his love interest.
- In The Loft, High-Class Call Girl Anne is initially hired by Vincent to seduce Chris in order to manipulate him into accepting a key to the loft. However, after this initial encounter, she falls in love with Chris and continues the relationship with him.
- The Mermaid have the titular mermaid being assigned to infiltrate human society in order to assassinate a property tycoon whose project is harming the merfolk community. But after she accidentally knocks herself out cold while repeatedly failing to kill him, the oblivious tycoon takes her home (mistaking her to be a drunk) and they started developing feelings for one another, to the point where she saves his life when he's abducted by the other merfolks who wants him dead.
- The Music Man: Harold Hill falls in love with both the townspeople in general and Marion specifically. In his own words, "for once, I got my foot caught in the door"
- Barbara Stanwyck does this in both The Lady Eve (where she's a cruise ship card shark falling in love with mark Henry Fonda) and Ball of Fire (where she's a lounge singer leading on Gary Cooper so she can hide out from the cops, until she isn't pretending).
- Mr. & Mrs. Smith (2005) zigzags this. It's inverted in the beginning, when the two titular characters, neither of them knowing the other is a secret agent, fall in love and only get the order to kill each other when they've already been married for a few years. At that point their marriage was failing, however, and for a while they really try to kill each other... only to fall in love again, playing the trope straight.
- Opportunity Knocks: while always attracted to Annie, Eddie didn't intend to fall in love with her...until he did during the love con.
- The movie Portrait Of A Hitman. Not exactly 'falling in love with' but he can't pull the trigger on her.
- Undercover Brother. After falling in love with the title character, Penelope Snow (AKA White She Devil) can't go through with killing him.
- Prizzi's Honor: Two highly skilled assassins are hired to kill each other. However, while trying to find the best way to complete their missions, they end up falling in love.
- Subverted in Red Eye. Jackson Rippner develops a Villainous Crush on his target Lisa but he continues to go through with his mission.
- The parents' backstory in Spy Kids. They were secret agents working for different countries, were assigned to "take each other out," fell in love, got married, settled down, had kids, got kidnapped by a Depraved Kids' Show Host...You know, normal parent stuff.
- In The Whole Nine Yards, Jill Saint-Claire is hired to kill Nicholas "Oz" Oseransky by Nick's wife. But as her plan to get close to Nick (in order to more easily kill him, of course) proceeds, she finds she likes him too much to actually go through with the hit. It's even discussed in a conversation between Jill and fellow hit-man Jimmy "The Tulip" Tudesky:
Jimmy: "Oz, you are the most chivalrous guy I've ever met."
Jill: "Do you see why I couldn't kill him?"
Jimmy: "Yeah... I love him!"
- When Jimmy is supposed to kill Oz, he can't do it either.
- In fact, he ends up killing a friend, another hitman, instead, although there are pragmatic reasons for that as well (he knew Frankie would betray him eventually).
- During the above conversation about "loving" Oz, Jimmy does mention a previous time he fell for a mark. He told the mark he was there to kill him. Unlike Oz, this one tried to kill Jimmy in response. Jimmy found he didn't love him anymore.
- When Jimmy is supposed to kill Oz, he can't do it either.
- Wild Target: The killer is initially unable due to chance to kill his target, but later he is bemused by her eccentricities and eventually falls in love and marries her.
- In Sonic the Hedgehog 2, it's revealed that Rachel's hunky fiancee Randall is actually a spy sent by GUN to capture Sonic and their entire wedding was a setup. Not helping that Commander Walters gleefully refers to the whole mess as Operation: Catfish. However, after Rachel goes on a rampage while her sister Maddie frees Sonic, Tails, and Tom, Randall takes a taser from the Commander for her. Randall reveals that he did end up falling for her for real, and they share a kiss, confirming their relationship.
- In Die Alchimistin, Gillian, a professional assassin, is assigned to kill his master's Arch-Enemy and the latter's young daughter Aura. The first murder goes off like a charm, but then Gillian meets Aura, and the two are instantly drawn to each other. Despite attempting to kill her, Gillian can't bring himself to finish the deed and lets her go, turning against his master. Later he and Aura become lovers.
- The heroine of The Assassins of Tamurin series ends up falling in love with the prince she was sent to kill and renouncing the teachings of her Evil Cult.
- In Assassin's Pride, the female lead, Melida Angel, is an apparent Muggle Born of Mages. Since most believe such a thing to be impossible, her family suspects her of being an illegitimate child and orders Guild Jack Raven to dispose of her unless by some miracle her mana awakens before they can kill her. The male lead, Kufa Vampir, is the assassin they assign to fulfill this mission. After Melida impresses him with her sheer determination, he decides to cheat and uses a Super Serum to awaken her mana artificially. He gradually develops increasingly inappropriate feelings given his real job, knowing all the while that if Melida's family or his guild ever find out what he did, they will almost certainly kill him with her.
- A minor example from the BattleTech novel Close Quarters: Protagonist Cassie Suthorn isn't exactly sent to kill the Honorable Percival Fillington, Earl of Hachiman. Merely gather incriminating evidence of a conspiracy against her employer in which he is involved, which could easily lead to his death if it fell into the wrong hands. In the course of her mission, she doesn't precisely fall in love with him, either, but he does inadvertently get past her own defenses enough for her to realize that he's after all an imperfect but fairly decent man whom the other sides in said conspiracy are using mainly as a highly-placed convenient pawn and with whom she could be friends if it wasn't for his being on the other side (and for her own deep-seated psychological issues). It motivates her enough that after her recovery she argues with her employer in favor of sparing him, and since her "impertinence" amuses Chandrasekhar Kurita, Percy does in fact get to live and even keep his position as though nothing happened. Until the next book, anyway...
- In Cloud of Sparrows, Heiko (the most beautiful woman in Japan) was hired to seduce and assassinate Genji. She fell in love with him, and he wasn't fooled in the least. Her boss lied to her. He wanted her to fall in love with him, and vice versa, to make his revenge nastier. It worked!
- In Corrupting Dr Nice by John Kessel, grifter Genevieve falls in love with Owen, the wealthy but naive biologist whose pet dinosaur she and her father are trying to steal. Subverted in that he rejects her when he finds out what her profession is. As revenge, she woos him all over again under a false identity, then does everything in her power to hurt him after they're married. They eventually reconcile, though.
- Cawti from Steven Brust's Dragaera series was a highly skilled assassin, who was hired to kill Vlad Taltos (she succeeded, but he got better) and ended up marrying him.
- In Grave Mercy, Ismae is ordered to accompany Viscount Gavriel Duval to court in order to uncover plots against the Duchess and kill the perpetrators. The Abbess, Ismae's superior, is convinced that Duval is a traitor; she expects Ismae to find evidence of his guilt and promptly kill him. Eventually, it becomes clear to Ismae that Duval's true allegiance is to the Duchess. He honestly has nothing but her best interests at heart, and is indeed the more or less the only person who does. However, due to misinformation, the Abbess finally flat-out orders Ismae to kill Duval. Ismae refuses to do it, mostly because Duval is innocent, but the fact that she's fallen in love with him certainly influences her decision to disobey.
- How a Realist Hero Rebuilt the Kingdom: Downplayed with Juna Doma. She was initially sent as a spy by her grandmother, Duchess Excel Walter, to determine Souma's suitability as the new king of Elfrieden. Becomes Hilarious in Hindsight when it is revealed that Excel warned her about falling in love with Souma, only for Juna to brush that off by saying that she "wouldn't let some man get to her". Excel later repeated those same words to her before the two went to participate in the Amidonian war, much to Juna's embarrassment. She ends up asking to marry him as a reward for her military service in the war, and becomes his first secondary queen.
- In Death series: Averted. Memory In Death has Eve Dallas finding out thing Bobby Lombard married Marnie Ralston, who was pretending to be Zannah. Marnie only married him because she was trying to hurt his mother Trudy Lombard as well as steal her stuff. Then she impulsively killed Trudy, tried to cover it up, as well as attempting to kill Bobbie for kicks. Eve has to tell Bobbie about all this, and warns him that she will use this trope to manipulate him. Naturally, he is unable or unwilling to believe what she's telling him.
- Logan's Run: At first, Logan was just using Jessica to lead him to Sanctuary, so he could destroy it and become the greatest Sandman who ever lived. But her bravery and will to live make an impression and she ends up as his Morality Chain instead.
- The tale of Amor and Psyche, a story-within-a-story in the Metamorphoses by the Roman author Apuleius (2nd century A.D.), makes this trope Older Than Feudalism at least.
- In the Discworld novel Mort, the human apprentice Mort, covering for Death, is sent on an assignment to claim the soul of the princess Keli. Poised with the sword (for royalty), he decides he cannot do it, as she is too young and attractive. And the consequences of Death declining to take just one soul reverberate around the Discworld...
- Rebuild World:
- Played With when the Cyber Ninja Nelia asks Akira to be her lover for the seconds it will take her to kill him, prompting him to call out her seeming Insane Troll Logic. Later development for her character shows that this is a result of her Consummate Professional mindset that values I Gave My Word above all else.
- A slum girl Alna pickpockets Akira and then manipulates Katsuya into defending her from him with lies. Alna was initially attracted to Katsuya but proceeded to manipulate him anyway, before she eventually gives him an Anguished Declaration of Love admitting to everything before Redemption Equals Death at the hands of Akira.* In Scarlet, Wolf's purpose was to gain the titular character's trust, coax secrets out of her, and then hand her over to be tortured and killed. Thanks to The Power of Love, he manages to overcome his More than Mind Control to save her.
- Robert Sheckley seemed to like the trope, as he has several rewritings of a story based on it. It is set Next Sunday A.D., when anyone can join the so-called Hunt. Five times you have to become the Hunter, hunt down and kill the Victim, and five times you are the Victim and have to try and kill your Hunter. Sheckley flipped genders of his characters and changed the ending several times, but the ultimate idea is the same: the Hunter falling in love with the Victim and refusing to kill him/her.
- A Song of Ice and Fire has a variation. Sometime after his exile to Essos, Jorah Mormont agreed to serve as a spy for Varys, and was ordered to get close with the last of the Targaryens: Viserys and Daenerys. While he has no love for the former, he eventually falls in love with the latter and saves her when she is about to be poisoned by an assassin who wants to claim Robert Baratheon's reward for killing her unborn son, even though it was Jorah who relayed the information in the first place. Regardless, when Daenerys learns about his former allegiance in the third book, she understandably feels betrayed and banishes him under the threat of death.
- In The Stolen Throne, Katriel is hired by an Orlesian mage named Severan to infiltrate Maric's rebel army and lead them to their doom, presumably killing Maric as well. However, Katriel ends up falling for Maric (even though she does initially lead the army into a trap, resulting in the death of the Arl of Redcliffe) and, eventually, betrays her employer. Maric kills her anyway, after some urging by Loghain, and never forgives himself for it. Katriel seems to forgive him, though, and even helps him in the next book as a spirit.
- In 'Five Survive', Arthur was ordered by his mafia family to befriend Red to get her to reveal her secret about her upcoming testimony. He ended up falling for her and became protective over her.
- Dianora from Tigana plans her entire life out to kill Brandin for destroying her hometown and removing its name from people's minds, but when she finally manages to make it to his harem, and into his bed, she can't go through with it because she loves him desperately.
- In The Unexplored Summon://Blood-Sign, Kyousuke had been trained since birth to become a summoner capable of killing the White Queen. Though he realized early on that he wanted nothing to do with his father's plot, he had no choice but to go along with it...until he actually met the Queen and she offered to help him out. The rest is (rather bloody) history.
- Battlestar Galactica (2003): The Cylon eventually known as Caprica Six was sent to seduce Gaius Baltar so he'd give her access to the Colonial Defence Network. In the process she genuinely fell in love with him and shielded him from the initial bombing of the colonies, ensuring he would survive while her current body didn't.
- Buffy the Vampire Slayer:
- Spike, who shows up in Sunnydale to kill Buffy, ends up falling in love with her.
- Anya originally appears with the intention of cursing Xander who cheated on Cordelia.
- On Castle, a con artist is murdered because he falls in love with his rich fiance and his partner in the con kills him to try to earn the money.
- Cole (Belthazar) from Charmed was originally sent to kill Phoebe (and her sisters) but ends up falling in love with her.
- In a CSI episode, the victim's wife and secretary are revealed to have been planning on poisoning him for years in order to split his fortune (they previously did this to the secretary's rich husband). Unfortunately for the secretary, the wife actually ended up falling in love with him. The secretary still killed him, though, and both get off scot-free. The wife doesn't seem too broken up about his death, however.
- In a CSI: Miami episode, Sheriff Anita Torres becomes the target of "El Asesino", a Mala Noche assassin, due to her work in putting out Mala Noche members in prison. It turns out that "El Asesino" is actually Anita's husband, who met her at the shooting range after receiving his orders but fell for her and chose to fake his death to see if that would convince her to stop working as a cop and keep her safe.
- Alec from Dark Angel fell in love with the daughter of the mark. The mark was later expanded to include her.
- River Song from Steven Moffat's run of Doctor Who: she fell in love with the Doctor, despite having been kidnapped as an infant, raised and trained specifically to destroy him. In their first meeting from her perspective, she came very close to killing him permanently, but ended up sacrificing her remaining regenerations to save him. In the end, her "owners" resort to just grabbing her and sticking her in an automated suit. And she still finds a way not to shoot him.
Tasha Lem: They engineered a psychopath to kill you.
Eleventh Doctor: Totally married her.
- On General Hospital, female FBI agents can't seem to help but fall for the mobsters they're trying to send to prison. Sonny Corinthos actually slept with two such agents (one died and the other was Reassigned to Antarctica), and a third lost her job after falling for Spinelli.
- This is the origin story for Christopher Chance, the Human Target, including the Innocent Bystander who saw too much, former colleagues, and the Contract on the Hitman. Unfortunately, it ends badly for the love interest, who dies before the end of the episode.
- An episode of the show, however, has this trope go somewhat better for another spy/assassin, who upon being ordered to kill her husband of three years (who she originally married as part of a long con), instead plans to fake both their deaths. (Then the husband hires Chance to protect him from her, not knowing anything about said plan.)
- Mickey makes the same mistake in Hustle, feeling sympathy for a bitter ex-wife he's targeting. She end up using him to take further revenge on her ex-husband, smearing for a crime it turns out he's innocent of.
- Imposters has Maddie, a con artist who specializes in marrying men (and the occasional woman) and then taking them for all they have. When three of her exes track her down, Maddie insists she felt nothing for any of them and it was just part of the job. However, in season 2, she admits to a therapist that in order for the cons to work, she had to let herself feel "just a bit." The therapist points out love isn't just something that can be turned off like a tap and deep down, Maddie basically loved every one of her marks.
- In From the Cold: Anya got close with Faina, whose father was giving secrets to the Chinese, on the SVR's behalf. Before long though Anya came to love Faina, with her reciprocating. She's clearly unhappy with her mission once this happens. After having to kill Faina, she holds her body and sobs.
- On Leverage, during "The Lonely Hearts Job" a con artist falls in love with her rich husband and ends up disappearing to try to protect him, kicking off the episode.
- The whole premise of The Mandalorian is a platonic take on this. The eponymous Mandalorian is a bounty-hunter, hired to kill a toddler. He ends up adopting said child.
- Medici: This happens to Maddalena, sent to seduce and spy on Cosimo de Medici during his exile in Venice.
- Motherland: Fort Salem: Scylla has fallen for Raelle genuinely, despite it being only meant as a honey trap to seduce her into The Spree. At the wedding after her superiors commanded that she bring Raelle to them, Scylla is shown having flashbacks over their moments together, and is clearly unable to. She tells Raelle she's in love with her, and always will be, then vanishes under cover of the chaos The Spree attack causes.
- Well, he's not a hitman, but in NCIS, Tony starts dating Jeanne because he's on a mission tracking down her criminal father. This gets rather complicated when he falls in love with her for real when she still doesn't know who he really is. After Jeanne's father dies, she asks Tony if any of it was real. Even though he really loved her, he tells her that it was all an act, so that she can move on with her life.
- In Orphan Black, a few different monitors have ended up falling in love with the clones they're meant to be observing. Paul doesn't quite count, as he fell for one he wasn't assigned to, but Donnie and Delphine both genuinely love their targets. In Donnie's case, it's easier, as he was already with Allison when he was given the job of monitoring her. It's a lot more complicated for Delphine, who might not have even been attracted to women before she met Cosima and who constantly had her care for her target used against her by her superiors.
- Our Flag Means Death: Bored with his current life, Blackbeard plotted to kill Stede Bonnet and take his place in society. However, as they spend time together, he grows fond of Stede and abandons his original plan. Eventually he finds he has fallen in love with the man, and offers to run away with him.
- Star Trek: Picard: Defied; Narek falls for Soji and even tells her his real name (which a Romulan would only disclose to someone they're in in love with), but duty always comes first for a Romulan (especially for a spy), so he still carries out his orders to murder her, and he cries as she pleads for her life.
- In both the mini-series and movie versions of State of Play, Sonia Baker is sent in by the company Stephen Collins is investigating to be his personal assistant - thanks to politicians working with that company - and report back on him. She falls in love with Collins - even getting pregnant by him - and tells the company she wants out. Tragically, Collins finds out who she really was, and the Psycho for Hire working for him has her killed.
- On Teen Wolf, hot twins Aiden and Ethan are sent by Deucalion to seduce Lydia and Danny, because one of them will supposedly be very important to Scott. Ethan quickly falls in love with Danny, much to his brother's annoyance. However, Aiden subsequently proves to care for Lydia as well, leading to both twins doing a Heel–Face Turn.
- In the Colombian telenovela Yo soy Betty, la fea, Armando and Mario device a plan for Armando to gain control of his parents' company by using Betty's knowledge of economics to their advantage, and use the fact that she has a crush on Armando to make her their Unwitting Pawn. While Betty is ecstatic that such a handsome man is showing interest in her and fantasizes of him breaking off his engagement to be with her, Armando is disgusted over the fact that he has to romance "ugly Betty". However, as they continue their affair, Armando begins to empathize with Betty after she told him that she had lost the ability to trust others due to the fact that she was bullied because of her appearance, and because the last boyfriend she had bragged about how he was the man "brave enough" to have sex with her, and Armando slowly starts develop romantic feelings for her. Eventually, this comes undone when Betty finds a letter from Mario to Armando outlining their plan, that they would use Betty's economic savvy to take over the company, dump her, and give her a big severance package when they fire her as way to cover their tracks. Armando then becomes despondent when Betty starts to ignore him, and refuses his romantic advances, and slips into a deep depression when Betty reveals Armando and Mario's plan in a board member's meeting, though it is mostly over the fact that Betty quits right after the meeting, and tells him off saying that she's come to hate him after he lied about loving her. When he says that he really did fall in love with her, she refuses to believe him, adding he's no different than anyone else she's had to put up with in her life that belittled her for their own sick amusement.
- Evillious Chronicles: Though she fell in love with him before he became the mark, the lover of Nemesis Sudou in "The Last Revolver" is quite important to her, though this doesn't stop her from killing him when she's ordered to. She turns the gun on herself afterwards and survives. After this, she decides to "confront" her boss.
- In Demon: The Descent, more than a few Demons Fell when an Angel tasked with manipulating or sacrificing a human came to love them and broke their connection to the God-Machine to protect them. This doesn't have to be an explicitly romantic or sexual connection, though. For example, an Angel might be tasked with adopting an orphaned child and sculpting them into a cult leader, with an eye towards a People's Temple style mass suicide to achieve one of the God-Machine's goals, and end up breaking free of the God-Machine to protect their child.
- In Dragon Age: Origins, Zevran is a potential romance option if you spare him after his failed assassination attempt. Justified because it's just business to him and his employers will kill him for failing his mission no matter what he does, so he has no ill will against you. It also helps that he didn't like the assassins guild he worked for and took the mission against you because he thought you'd kill him and, after you spare him, he realizes that you just might be powerful enough to take on the hit squad that will be sent after him for his failure.
- In one of his first missions for the Crows, Zevran ended up sleeping with the Mark. While he didn't fall in love her she had convinced him to talk to his employers about her. Instead she tripped and fell on her head, killing her instantly. Zevran was applauded for making it look like an accident. He wasn't too cut-up about it, as he discovered afterwards she had planned on double-crossing him.
- Also present with the male Warden's romance with Morrigan. She wasn't hired to kill you, but she did intend to be impregnated by you so she could give birth to an Old God. When you find this out and ask Was It All a Lie?, she admits that "loving you...was not part of the plan."
- Fire Emblem:
- Fire Emblem: The Blazing Blade has Jaffar and Nino. A catch here is that they're both assassins in the organization now run by the Big Bad— and are sent to assassinate the Prince of Bern, Zephiel (a hit put out by the Prince's Fox-kicking Bastard of a Father). However, the organization can't exactly get away with killing someone that important... so Sonia orders the up-to-that-point completely heartless Jaffar to kill her own daughter Nino as a scapegoat for the murder, apparently unaware that Nino had actually saved Jaffar's life in the recent past. Needless to say, that didn't go over well in more ways than one. Ultimately, this leads to a double Heel–Face Turn and if they get an A-Support, they'll end up married (Although, neither lives much longer after the game, sadly.)
- In Fire Emblem: The Sacred Stones, Joshua meets Natasha and attempts to flirt with her; she runs off, keenly aware of the bounty on her head as a Defector from Decadence. When they meet up later, he flips a coin and tells her to call it in order to determine whether he kills her or not. Note that she is a cleric who is bound by oath not to indulge in vices such as gambling (though this is an understandable excuse), and it's heavily implied Joshua actually lost on purpose because he didn't really want to kill her. They get married if they achieve an A support.
- A weird variation can happen in Fire Emblem: Awakening. Princess Lucina went back in time to save her father Chrom, who was murdered by his closest friend The Avatar after they're possessed by Grima. However, she doesn't realize at first that the Avatar is the killer, and if the Avatar is a guy and isn't married by the time she arrives, she can potentially fall in love with him before either one knows that he's the mark. If this happens, it leads to a heartbreaking scene for the two later when Lucina tries (and fails) to kill him.
- Bastila in Knights of the Old Republic. Her real purpose was to watch over the amnesiac Revan to make sure he didn't start to recall any of their former life as Dark Lord of the Sith. Falling in love with him however, wasn't part of the plan.
- Visas Marr in Knights of the Old Republic II: The Sith Lords joins your party after failing to assassinate you. She is a possible love interest for a male character (though the Handmaiden becomes inordinately jealous).
- Played with in Mass Effect 2: Thane fell in love with the woman that blocked his shot on the Mark. According to Thane she didn't even know his target, and this had a profound affect on him (he still took the shot, just not that day). He tracked her down, begged her forgiveness, and they eventually married.
- A rather twisted version of this trope appears in Metal Gear Solid, in which Sniper Wolf is known for becoming so obsessed with her targets that she falls in love with them... right before she kills them anyway.
- Metal Gear Solid 3: Snake Eater: This one's tricky. Eva is actually a double agent for China. She becomes grossly entangled with Snake, even though she has to kill him at the end of the game to silence his report on the $100-billion legacy. The thing is, she doesn't spare him because she loves him - her spy school trained students for that A LOT. She spares him because HIS mark, who he killed, was an espionage teacher to both of them - and basically, she loves The Boss even more as a stepmother.
- Metal Gear seems to love this trope. In Metal Gear Solid V, whether or not Quiet actually fell in love with Big Boss and therefore defected to their side is a matter of debate, but Ocelot pretty much says this verbatim when questioning the assassin after learning her true identity and original goal. Miller argues that they shouldn't take any chances and get rid of the assassin, but Ocelot argues that they have proven their loyalty because they could have killed their mark at any time. He states the assassin fell in love with Big Boss's legend, and he knows because he was the same way once.
- A variation of this appears in NieR: Automata: It's eventually revealed at the end of the game that 2B is actually 2E, which stands for Executioner: a special class of androids made to kill any other YoRHa units that go rogue in some way. Specifically, she's the personal executioner of 9S, who as a Scanner type has a tendency to look too deep and find out things he shouldn't, but who YoRHa still wants to keep because his skills in reconnaissance are invaluable. Any time 9S probes too far, 2E is ordered to kill 9S and wipe his memories. What makes things bad for her is that 9S really, really tries to get close each and every single time they get on a mission together, and as a result 2E started to gain genuine affection for him, causing her to eventually hate every single time she has to kill him even if she does it anyway. This single bit of knowledge brings new light on every single line of dialogue 2B and 9S have earlier in the game.
- In Sacred, two of the PCs, the Dark Elf assassin and Wood Elf ranger, are lovers. The Dark Elf was supposed to murder the Wood Elf as a rite of passage, but his love for her turns him into a Defector from Decadence.
- The backstory of Kasuga from Sengoku Basara reveals that she fell in Love at First Sight with Uesugi Kenshin, the man she was supposed to assassinate and promptly underwent a Heel–Face Turn for, and has been serving as his bodyguard ever since.
- XIII has one (female) assassin tell XIII that the #1 rule for assassins is not to fraternize with the target, so as not to hesitate at the time of killing. Which of course doesn't stop her from sleeping with him.
- In Yakuza 0, Goro Majima is tasked with performing a hit in order to be allowed back into the Tojo Clan, only for him to learn that his target is a blind woman. Unable to go through with it, his goal then shifts to protecting her from as she becomes embroiled in a bloody power grab. Later on, it's revealed that his boss Shimano was actually trying to invoke this, knowing that Majima could never go through with the hit and was counting on the two to develop a bond so he could get her to sell the Empty Lot to Shimano. Eventually, he and Kiryu succeed in protecting her, but he ultimately leaves her in the hands of her physician after making him promise to protect her while she remains grateful to the mysterious stranger who helped her.
- Madame Outlaw: Heath is a mercenary contracted by the Montesquieus to ensure that Estelle disembarks in New Orleans, so she can be "returned" to her husband. He winds up falling for her spirited nature and helping her escape him.
- In The Order of the Stick, Daimyo Kubota assigns the half-orc ninja Therkla to kill Elan, who is acting as a bodyguard for Kubota's ultimate target, Lord Hinjo. Therkla develops a crush on Elan and is unable to bring herself to kill him, but she's equally unwilling to turn against her lord. She tries to Take a Third Option, but the hastily-conceived compromise she offers is one that neither party has any incentive to take, and when the negotiations inevitably break down Kubota fatally poisons her as a distraction for his Villain: Exit, Stage Left. She dies in Elan's arms, though she at least gets a badass petrified demon as a tombstone.
- Arcane: Mel originally cozied up to Jayce because she sees him and his Hextech as a golden goose, but grows fond of his honesty and unconditional kindness. To the point where she ultimately chooses to reject her mother’s suggestion to manipulate him to make Hextech weapons.
- Something like this is used in The Zeta Project, in a non-romantic way. Zeta is a literal emotionless robot who is designed to infiltrate and eliminate targets without their being aware of the deception. However, after impersonating a man for months, Zeta bonds with the family and develops a heart. Deciding he doesn't want to deny the man a chance to see his daughter grow up (or indeed hurt any living thing again), he abandons the mission and goes on the run. This kicks off the main plot.