In Love with the Mark

""Do what? Do I ice her? Do I marry her? Which one of these?""

- Prizzi's Honor

The Career 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. Of course, 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 cum 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. It seems the old assassin's maxim "Don't get involved with the mark, it can get messy" is putting it mildly.

Another Moral 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.

Anime and Manga

 * Rethink your definition of "love", and you have Seishirou Sakurazuka from Tokyo Babylon and X 1999.
 * Crying Freeman has Emu Hino, who saw Yoh Hinomura for the first time right after he murdered one of his targets. She was singled out for death... but she and Yoh fell in love and ran away together.
 * Rolo in Code Geass develops a strong, genuine affection for Lelouch Lamperouge while posing as his younger brother to monitor him and saves his ass.
 * Ironically played with in Rurouni Kenshin. Assassin Kenshin and Tomoe fall in love with each other. However,
 * 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.
 * One episode of Noir has Kirika befriending a target..
 * 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.

Fan Fiction

 * The somewhat, um, 'infamous' Warhammer 40000: Dawn of War fanfiction "Love Can Bloom".

Film
"Jimmy: "Oz, you are the most chivalrous guy I've ever met."
 * Played with in Grosse Pointe Blank. The hitman is actually in love with
 * Aeon Flux. It's a Justified Trope because
 * Mr. and Mrs Smith inverts this. The two characters fall in love and get married, neither knowing the other is a secret agent, and then later, they're instructed by their respective organizations to kill each other.
 * The movie Portrait of a Hitman. I don't know about 'falling in love with' but he can't pull the trigger on her.
 * Undercover Brother. After falling in love with the title character,  can't go through with killing him.
 * 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 lampshaded in a conversation between Jill and fellow hit-man Jimmy "The Tulip" Tudesky:

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, although there are pragmatic reasons for that as well.
 * Prizzi's Honor.
 * Wild Target, he is initially unable due to chance to kill her, but later he is bemused by her eccentricities and eventually falls in love and marries her.
 * This occurs off-camera in the movie Conspiracy Theory
 * 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.

Literature

 * 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.
 * Cawti from Steven Brust's novels was a highly skilled assassin, who was hired to kill Vlad Taltos and ended up marrying him.
 * 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.
 * 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 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
 * 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.

Live Action TV

 * Cole (Belthazar) from Charmed was originally sent to kill Phoebe (and her sisters) but ends up falling in love with her.
 * Alec from Dark Angel fell in love with the daughter of the mark. The mark was later expanded to include 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.
 * 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.)
 * from Steven Moffat's run of Doctor Who:.
 * On Buffy the Vampire Slayer, Spike, who shows up in Sunnydale to kill Buffy, ends up falling in love with her.
 * On Leverage, during "The Lonely Heats Job" a con artist falls in love with her rich husband and ends up disapearing to try to protect him, kicking off the episode.
 * 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.
 * 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 secreatary still killed him, though, and both get off scot-free. The wife doesn't seem too broken up about his death, however.

Video Games

 * 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 Dragon Age, 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.
 * 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.
 * Visas Marr in Knights of the Old Republic 2 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, eventually tracking her down and marrying her.
 * 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). They get married if they achieve an A support.
 * And from Blazing Sword (7), we've got 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 order the up-to-that-point completely heartless Jaffar to kill her own daughter Nino as a second target, 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 1. 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.)
 * 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.
 * 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.
 * 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.

Web Comics

 * In Order of the Stick's, the half-orc ninja Therkla is ordered by Lord Kubota to kill Elan (in order to get at Hinjo, for whom Elan is currently working as a bodyguard). Therkla instead develops a crush on Elan, defects, and is ultimately killed by Lord Kubota. Elan is unable to prevent this, and takes it kind of hard.

Western Animation

 * Something like this is used in The Zeta Project, but it's not romantic love. 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.