Romantic/sexual relationships between cousins are a phenomenon that has been more accepted in some cultures and eras than others. A great many cultures today accept it, including a majority of the industrialized world. Marrying one's extended relatives (which is technically known as clan endogamy) seems to have been common in human evolutionary history, since hominids usually lived in small nomadic bands with few available sexual partners. At the other end of the spectrum, much of the modern U.S.A. considers cousin marriage completely taboo, so Hilarity Ensues at the very mention of it. People from backwoods areas (especially the Appalachian Mountains) are often the preferred butt of many bad jokes as well as occasional bits of Self-Deprecating Humor for the alleged prevalence of Kissing Cousins in their culture. Despite the taboo, cousin marriages are legal in about half the states in the U.S.A., though not as much in the backwoods areas and more in the modern industrialized states, the opposite of what one might expect from hearing all those jokes. Legal or not, these marriages are still not very common due to the lingering cultural taboo.
Some cultures distinguish between parallel cousins — one's mother's sister's child or father's brother's — and cross cousins — mother's brother's or father's sister's. Cultures in which a parallel cousin is taboo often regard the cross cousin as the best possible choice of a spouse, since the marriage will strengthen bonds among members of the bloodline and ensure that property remains in the family.
Most of the origins of the cousin marriage taboo are not inherently religious; the ancient Hebrew patriarchs demonstrably had no problem with cousin marriage at all (Isaac married Rebekah, his first cousin once removed). The largest Christian denomination, the Catholic Church, allows even first cousins to marry with special dispensation. First-cousin marriage is perfectly fine under Islamic law and some Middle Eastern and Central Asian cultures actively encourage it. Hinduism, Buddhism, Confucianism, and Asian animist traditions have little to say against cousin marriages either.
One culture in which clan endogamy was primarily tabooed was medieval Europe; this prohibition extended as far as third cousins and included in-laws. In a chronically violent culture that put a far higher value on tribal and dynastic bonds than we do today, this was much more about trying to mitigate warfare by extending people's social networks than preventing inbreeding. This led to royal or noble families seeking to end blood feuds by marriage alliances often needing dispensation from the Church to marry — as, for instance, Henry VII and Elizabeth of York at the end of the Wars of the Roses. (Coincidentally, it was Henry VII's son Henry VIII who put an end to this in England by breaking from the Catholic Church: The Church of England notably omitted first cousins when listing which relatives were covered by incest prohibitions.)
This was also the case in China, in a historical period analogous to that of feudal Europe; nobles were explicitly banned from marrying any person that could trace their paternal lineage to the same historical tribe (effectively, anyone with the same family name). This was then extended to all social classes after the unification of the Chinese empire; people bearing the same surname were forbidden to marry even if they were not related at all. However, cousins with different surnames were allowed, and in many cases encouraged, to be paired together to strengthen the alliance between two clans during said period. Linguistic remnants of this tradition may still be found in some areas in Southern China, where the form of address used for one's mother- and father-in-law may also be used to address one's uncle and aunt.
Thanks to the discovery of the laws of genetics a fairly modern part of the taboo against cousin marriage is the perception that this form of inbreeding results in heightened risk of offspring with genetic disorders like hemophilia or albinism. A study in Western Australia discovered that while the risk of a serious defect does rise slightly, the change isn't that dramatic (i.e. a 4% risk for first-cousin parents instead a 2% risk for unrelated parents, roughly equivalent to the risk of birth defects in children conceived by women age 35 and older as compared to children conceived by women under 35) Please note, however, these statistics apply only to first cousins: any couples more distantly related are likely to be as genetically dissimilar as randomly paired individuals from the general population (how many of your third cousins do you even know?).note On the other hand, getting any closer than first cousins is quite dangerous, because relatedness works on an exponential scale. An uncle-niece pair share 1/4 of their genes as compared to 1/8 for first cousins, and full siblings on average share 1/2 their DNA. And the first-cousin marriages studied were one-time occurrences, those statistics don't cover an entire family tree doing it for generations like has been seen in certain aristocratic populations—repeated, exclusive endogamous marriage is likely to have more serious genetic consequences.
Expect some strongValues Dissonance between the media from the US and other countries, and between certain modern works and works from the nineteenth century and earlier, when the taboo was sometimes non-existent or even inverted. Full scholarly debate on why some cultures would forbid cousins, or even specific types of cousins, to marry, while others ignore or even encourage it, rages on, and lies beyond the scope of this wiki.
According to both Oxford's and Merriam-Webster's Dictionaries, the original definition of kissing cousins was simply a relative known well enough to be given a kiss in greeting, although this has fallen by the wayside.
Check out Incest Is Relative for more closely related tropes.
NOTE: This trope is for cases of actual relationships between cousins. Incestuous subtext goes in Incest Subtext.
For Real Life examples, see The Other Wiki for cousin marriage.
In Sword Art Online the player, Leafa, is actually Kirito's cousin Suguha, though they were raised as siblings, Suguha became interested in Kazuto after finding out they weren't siblings, just cousins. Suguha tried to give up on him since he was obviously in love with his girlfriend Asuna, so she, as Leafa, began to develop feelings for Kirito. Suguha never knew Kirito and Kazuto were the same person until Kirito tells her he has to find Asuna and she is naturally shocked and upset that she fell in love with her cousin twice and the feeling isn't mutual.
In Ayashi no Ceres, Kagami claims that there's been a lot of this in the Mikage family line, although it's worth mentioning the context seriously calls his credibility into question: he's trying to provoke Ceres into emerging from his cousin Aya by coming on to her, taunting her with this claim, and attempting (or at least pretending to attempt) to rape her.
In Nerima Daikon Brothers, Hideki has a crush on his cousin Mako, who in turn is attracted to her cousin (and Hideki's brother) Ichiro.
In Blade of the Immortal, Kagehisa Anotsu's true love is the swordswoman Makie Otonotachibana. Her grandmother was the younger sister of Anotsu's grandfather, which makes them second cousins.
In Naruto spin-off series Rock Lee's Springtime of Youth, Neji is implied to have more than just familial affection for Hinata, because there is a scene where he imagines the story of Romeo and Juliet, in which he casts himself as Romeo and Hinata as Juliet. In his fantasy, they're called Nejio and Hinaette and look at one another with sparkles in their eyes, before they run towards each other and embrace lovingly. In the same series, he gets so angry when he hears about Hinata trying to date Naruto, that he attacks Hinata in fury, and it's not just the big brother instinct anymore, but plain jealousy. Bear in mind that their fathers were identical twins, meaning that Neji and Hinata are even more closely related than would normally be the case for first cousins.
Neji: Never... you and Naruto... doing things like that... it's... an infamy!
There is also issue 20, where Neji gets a severe nosebleed when he hears about Hinata's breasts getting even bigger than they already were.
He also acts like a pervert towards the female characters in the Road To Ninja alternate universe movie, including Hinata. Preview scenes and the trailer show that he acts like this especially towards Hinata.
Hanamori Pink did a short story called Cherry ♥ Blossom where the main couple were cousins. In fact, it's because they're cousins that they're able to save (the love lives of) their entire school by calling on the powers of their ancestors. It was published with other short manga in Japan, but the only official English translation is as an extra in the last volume of Mermaid Melody Pichi Pichi Pitch.
Likewise when NelvanaMacekredCardcaptor Sakura into Cardcaptors they made two of Sakura's classmates who were clearly fond of each other, with a snarky, cute relationship, into cousins. Whereas they removed the fact that Meiling and Syaoran were cousins by changing Meiling's surname to Rae.
Sakura and Tomoyo are second cousins, although their mothers, Nadeshiko and Sonomi (respectively), definitely fell into this trope. Or at least Sonomi wished they did.
And by cousin you mean that she's her mother's older sister's husband's uncle's third daughter.
Played With in Fruits Basket. Several of the couples consist of two members of the Sohma clan, and they often call one another "cousins", but the family is roughly the size of a small town. Considering how small the families tend to be (and that none of the characters' parents are ever implied to be siblings), the couples are probably only distantly related; they just call each other "cousins" because it's simpler than "third cousin twice removed".
In Narutaru, Shouko Fukuyama has these feelings for her cousin Kyouji. Hell, she has it bad for him; she's about 13 years old and wants to bear his children. She has an It's All Junk hissy fit after being told off by his old crush Jyun. Eventually, Kyouji, who had been comatose for years, dies, and Shouko is all alone... until she sees him after he turned into a..."Virgin Princess" and vows to keep on loving him.
In the manga Sakura Diaries, the main character Touma's younger cousin, Urara, is constantly trying to sleep with him and keep him away from other women.
It's been mentioned in a Code GeassSound Episode that Suzaku Kururugi was engaged to his cousin Kaguya Sumeragi when they were children. Kaguya later decides that she is married to Zero, Suzaku's mortal enemy. What makes it particularly funny is that Suzaku eventually becomes Zero, though we don't know if Kaguya knows that.
In one of the earlier cases of Detective Conan, the killer's motive for killing his grandfather, etc, was he fell in love with his cousin, and the older man forbid them to marry. The killer's parents were also cousins, and the patriarch reluctantly agreed their marriage.
Suzuho in Macademi Wasshoi is Takuto's cousin, and naturally one of the haremettes fighting for his affection.
In Black Butler, Ciel is engaged to his cousin, Elizabeth. They get along quite well, in fact Elizabeth is one of the few things that Ciel seems to care about.
Which one of the girls in Onegai Twins is related to Maiku? In the manga, both of them. The one who isn't his sister turns out to be his cousin. They still get together, and if being cousins is an issue, they never say so.
In Venus Versus Virus, Sumire's male cousin, Riku, likes her. He's like ten years old, and she's fourteen.
Sachiko Ogasawara in Maria-Sama Ga Miteru is intending to marry her cousin Suguru after she graduates.
In a filler episode of Shugo Chara!, Amu admits that her cousin Shuu was her first real crush.
In the manga of Zero no Tsukaima the Prince of Albion, Wales, and the Princess of Tristian Henrietta are cousins who are in a secret affair (Long distance). Their love is cut short when Wales is killed.
In Mai-Otome 0~S.ifr~, it is revealed that Sifr is the daughter of the King of Windbloom's brother, and it is strongly implied that she eventually marries the King's son, Bruce.
Masahiko and Shion from Family Compo are cousins and there's often a sense attraction between the two. The manga starts with Masahiko saying Shion is cute, before he learns she's his cousin. Oddly the series keeps on swaying between Masahiko being Sora's and Yukari's parent figures, and whether Shion and him are Like Brother and Sister or are full Kissing Cousins.
The protagonist and his second-cousin in Hanayashiki no Juunintachi.
In Ten Yori Mo, Hoshi Yori Mo, Tadaomi's father and Mio's dead mother were siblings, so a Tadaomi/Mio match-up would be this. Tadaomi wants it badly to happen, but Mio does not.
Bleach: Pure-blood Quincies are expected to accept endogamous Arranged Marriages to prevent contamination of bloodlines even if it means marrying cousins. The Ishida matriarch engaged her son Ryuuken to his cousin when they were both teenagers. Ryuuken and Masaki cared about each other as family but were reluctant to marry because they knew they were romantically ill-matched. Not only was Ryuuken not Masaki's type, he was also more attached to Kanae than he was allowed to be.
Axis Powers Hetalia: Downplayed — Austria is the cousin of Germany and Prussia, and he gets a lot of Ho Yay with them, though the Official Couple is Austria/Hungary. He allows Germany to practice sexual activities with him, to prepare Germany for Italy.
Having a cast of Loads and Loads of Characters based on countries, most of whom are related in some way, makes this and other forms of Incest Subtext fairly common in the series (one of the Squick factors that drives some people away from the fanbase). Generally, however, it remains as downplayed as the above example - i.e., Prussia and the Holy Roman Empire are both children of Germania, and as Germany is Prussia's brother and Italy is Holy Roman Empire's grandson, this makes Italy something like Germany's second grandchild once removed (as well as his romantic interest)... This mostly results from the characters' Tangled Family Tree, though, and may not have been intentional.
A Cruel God Reigns: William has a fling with his second cousin, and it is implied that Lilia may have cheated on Greg with her second cousin.
The anime Resort Boin, based off the visual novel with the same name, has Daisuke and Maya, who are cousins, engage in sex a few times.
Marvel superhero Black Bolt, the king of The Inhumans, is married to his cousin Medusa. Sorta justified: due to the limited gene pool of the Inhumans, just about every two-Inhuman marriage involves cousins.
Mark Millar's post apocalyptic Wolverine story "Old Man Logan" features a future were Hulk and cousin She-Hulk have bred and produced inbred offspring. This is all due to her being the only woman able to "Take the pace" of Hulk sexually. Hulk and She-Hulk are both radioactive too, which probably didn't help...
Not the first time romantic/sexuality thing has been brought up between these two as some of Fixit's dialogue with her implies he's more than game.
It bears mentioning that there were implications that the relationship wasn't exactly... consensual.
Superman's future daughter engages in a literal example◊ in a Silver AgeElseworld story taking place in the future. (For those who don't know the Superman mythos, Lucy and Lois are sisters, which makes Lucy and Jimmy's son the cousin of Lois and Clark's daughter. Apparently, that doesn't bother Lola or Jimmy Jr, let alone their parents, happily watching them make out. The issue itself makes no mention of them being cousins, with the main obstacle to their happiness being It's Not You, It's My Enemies. They do live Happily Ever After in the end. As an Elseworld, it doesn't really count, but still... how this got past the radar is a mystery.)
The Man of Steel himself apparently had such feelings for his cousin Kara◊ (Supergirl). In that one, Kara tries to find Supes a girlfriend. After many failed attempts, we get the panel above, which seems to make it perfectly clear that the law is the only thing stopping them from pursuing a relationship (maybe they minded a lot less in the 60s?.) Eventually, Kara fixes Supes up with a girl that is nigh identical to herself, but older, and they hit it off. Unfortunately, it turns out yellow sun is her Kryptonite, and he can't leave Earth unprotected, so they must part.
Also, from the same source as Lex Luthor stealing forty cakesnote That's as many as four tens. And That's Terrible. comes Kara and Clark deserving a rest◊. Maybe it's just hard to make her look unsexy, but... that looks far from innocent, and the repetition, though intended to drill the definition into a kid's mind, really makes it sound like she is saying "We deserve a rest, nudge nudge wink wink," and the big blue boy scout just isn't getting it yet.
In yet another Silver Age Superman story, Clark has Kara disguise herself as a superheroine from another dimension, and she and Supes proceed to have makeouts (in front of Lois), all to fool some dim alien invasion. She was explictly underage at the time, too. Yeesh.
Namorita (daughter/clone of Namora, and therefore cousin of Namor) was in love with Namor at one point, though it was unrequited.
MAD's Monroe was once visited by his punky Scottish cousin, and they made out a few times. She decided she didn't want to see him anymore because of he was freaky with his "finger-skateboards", but as he said, at least he got to "make oot" that summer.
In the X-Wing Series, Plourr Illo was engaged to her cousin since childhood. In the arc where she returns to her homeworld and takes up the reins, she's shown resisting the idea of marrying him, but since he shows a number of her traits - lots of courage, love of fighting and freedom, disdain for tradition for tradition's sake - she warms up to him. It's never shown whether they actually get married at some point.
In the Douwe Dabbert story Florin the Loafer, count Justus van Bottericke attempts to force his cousin Gwendoline to marry him, because if she does not, he will lose the rights to his title.
Helene and Franz from a story by Wilhelm Busch. Despite him being a Catholic priest.
In the My Little Pony: Friendship Is Magic fanfiction, Maternal Instinct, the Changeling royal family, the House of Roachanov, has a reputation for practicing royal intermarriage, much like the European monarchies of old, ironic as the culture is predominantly of Imperial Japan. The Crown Princess, Pupa, is already set to marry her first cousin, Prince Morphin.
There's a fairly large following in the Phineas and Ferb fandom for the pairing of Marie Flynn (daughter of Phineas and Isabella) and Thomas Fletcher (son of Ferb and Vanessa)...even in universes where Phineas and Vanessa are half-siblings. And even in the more traditional worlds, there's still frequently Lampshade Hanging about "Isn't she your cousin?" "Step-cousin." All in all though, Thomarie is pretty cute...even if Marie is as oblivious as her father.
Western Animation/Ben10 has a rather large following for Ben and Gwen pretty much since the first series. This can be connected to the Bleached Underpants history of the original draft of the show in which Ben and Gwen were not relatives but rather in the same school class.
Belle-Etoile and her husband Cheri are double first cousins - their fathers are brothers and their mothers are sisters.
In the first written version of "Beauty and the Beast", Beauty and the Beast turn out to be double first cousins, their fathers being kings and brothers, and their mothers fairies and sisters.
The French fairy tale The Little Green Frog features a second cousin couple, Prince Saphir and Princess Serpentine. Their fathers are first cousins.
In many Arab fairy tales, reflecting common practices, a woman is normally expected to marry her first cousin. (One example of such a couple is found in The Story of Dschemil and Dschemila, which comes from Libya.) This causes serious complications when she falls in love with another man; some tales have men forced to leave a tribe lest it happen. However, some first cousins graciously concede; this is often resolved by the new bridegroom offering the first cousin his own cousin.
Colin, in The Secret Garden, wants to marry his cousin Mary when they grow up so that they can always be together. Mary is amused but uninterested. Colin's response is a jealous loathing of Dickon, the servant boy who helps them in the titular garden, with whom he suspects Mary of falling in love. In one film adaptation, their mothers are stated to be identical twins, thus making this even iffier genetically, since the offspring of identical twins are genetic half-siblings (assuming the other parents involved to not also be identicals, and to be two different people).
In the 1987 Hallmark adaptation adult Colin (portrayed by a very young looking Colin Firth) proposes to Mary at the end and she accepts.
In The Godfather Part III, Micheal’s daughter, Mary, and his nephew, Vincent, are in love. Michael is against their relationship, but Mary's mother, Kate, is not.
In the Victorian farce The Wrong Box, Michael tries to resist his attraction to his cousin Julia:note It turns out they were both adopted; her parents were missionaries and were eaten by their congregation.
Michael: We both know what kissing leads to, and if I may be blunt, our children would be idiots."
Dar and Kin in The Beastmaster. It's actually achieved through Fridge Logic; their relationship to each other is never noted at all in the film after the reveal that Dar is the son of Kin's uncle the King, and they don't see any problems in a romantic relationship by film's end.
In Tombstone, Doc Holliday tells Wyatt Earp that as a teenager he fell in love with his first cousin; she entered a convent over their affair.
In The Yards, Leo, the main character, had a relationship with his cousin Erica when they were younger. There is romantic subplot between the two throughout the movie.
In Mean Girls, Karen talks about what a good kisser her cousin is.
Karen: Yeah, but... he's my first cousin. Like, you have your cousins, and then you have your first cousins, and then you have your second cousins... Gretchen: No, honey, uh-uh. Karen: That's not right, is it. Gretchen: That is sonot right.
In The Lion King, Fridge Logic dictates that Simba and Nala must be either cousins or half-siblings because Scar and Mufasa are the only adult male lions in the pride.
The sequel defies this by specifically mentioning twice that Scar is not Kovu's father, though fans still speculate. Kovu was meant to be Scar's son but then they noticed that'd make Kiara and Kovu cousins.
The romance between Heather Mason and Vincent Cooper in Silent Hill: Revelation 3D. In the first Silent Hill film, Heather's biological mother Dahlia was the sister of the villain Christabella. In Revelation 3D, Vincent is the son of the villain Claudia, who is Christabella's sister. Therefore, Dahlia and Claudia are also probably also sisters and Heather and Vincent are probably cousins. It could be possible, however, that Dahlia and Claudia could be unrelated, if one were only a maternal half-siblings (uterine) and the other were only a paternal half-sibling (agnate/cosanguine). It's likely, however, that the writer of the second film missed the fact that Dahlia and Christabella were sisters in the first film. It's not the only Retcon.
Brought up humorously by Daisy in The Great Gatsby when her cousin Nick asks her to visit him to reunite with Gatsby and when she arrives, she discovers his house is full of flowers courtesy of Gatsby. She murmurs he must be in love with her.
In Jade Green, Charles lusts for his cousin Judith, and is secretly planning on raping and killing her after she rejects her advances, much like the the title character herself.
In The Silmarillion by J. R. R. Tolkien, the Elf Maeglin was in love with his first cousin Idril Celebrindal, who is squicked by this, for "the Eldar wedded not with kin so near, nor ever before had any desired to do so."
Also, Ar-Pharazôn, the last King of Númenor, married his first cousin, Tar-Míriel, against her will.
Aragorn and Arwen are first cousins several-times removed, as Arwen's uncle also happens to be an ancestor of Aragorn's many, many generations up the tree.note Elrond and Elros were both Half Human Hybrids. Elros identified with his human side and became the first King of Númenor, whose line descended to the Kings of Arnor and Gondor. Elrond identified with his elven side and got their functional immortality.
Galadriel and Celeborn are second cousins - Galadriel's maternal grandfather and Celeborn's paternal grandfather were brothers.
Sam Gamgee and his wife Rosie Cotton are third cousins. Sam's great-grandmother Rowan was the older sister of Rosie's great-grandmother Rose.
Merry Brandybuck's parents Saradoc and Esmeralda are second cousins. Saradoc's grandmother Mirabella and Esmeralda's grandfather Hildigrim were siblings (both children of Gerontius Took and Adamanta Chubb). Merry marries his third cousin Estella Bolger, who is the great-granddaughter of Hildibrand Took, another of Gerontius' and Adamanta's many children.
In Felix Salten's Bambi, Bambi and Faline are cousins (their mothers are sisters).
In the 1818 version of Frankenstein, Victor Frankenstein and his fiancée, Elizabeth Lavenza, are cousins who also happen to have been raised in the same household. In the 1831 version, Elizabeth was adopted rather than being related to Victor, but the two were still raised as siblings.
A central part of the plot in One Hundred Years of Solitude is the fact that the founders of the Buendía clan were cousins, and therefore they feared the family would sooner or later breed monsters if they ever in-bred from that point on. Despite all efforts, it happens anyway.
In Rose in Bloom, the only people that the heroine Rose even considers marrying are three of her seven male cousins, Archie (who falls for Rose's lady-in-waiting Phebe), Charlie "the Handsome" and Mackenzie, aka Mac. Rose's guardian, Uncle Alec, explicitly says that he does not approve of cousins marrying, while her aunt Clara—overheard and tactlessly quoted by yet another cousin—holds that Rose should marry one of them "to keep the money in the family." After Charlie dies, Rose falls for Mac and marries him, while Archie and Phebe finally overcome the family veto to their relationship. As a bonus, Archie's 12-year-old brother Jamie gives Rose a love declaration at some point, which she rejects not because he's her cousin, but because she sees him as Justa Kid.
In The Moonstone by Wilkie Collins, Rachel's has two suitors, both are her first cousins.
In the Kushiel's Legacy series by Jacqueline Carey, distant royal cousins (his father is her great-grandfather's brother) Imriel and Sidonie fall for each other. Hard. However, their relatives (and the nation at large) aren't so much annoyed at the idea of relatives marrying so much as they are annoyed that Imriel's mother tried to take over the kingdom (twice, orchestrating an invasion the first time around) and at least some of the populace (mostly the ones still healing the scars from the invasion) thinks Imriel would do the same.
In Rebecca the titular dead wife and her cousin, Jack Favell, were lovers. This relationship is presented to further underline Rebecca's depravity.
The Wilkes and Hamilton families in Gone with the Wind have the tradition of cousins marrying each other. The text makes it clear that multi-generational inbreeding is the main reason for Melly's frail health and physique.
The 1632 series has fun with this trope. The locals see nothing wrong with cousin marriage. The transplanted Americans are a lot more sensitive about this sort of thing (being from West Virginia, they've heard ALL the "inbred hillbilly" jokes).
In Anne Rice's Lives of the Mayfair Witches trilogy, 13-year-old Mona Mayfair has a list of the male cousins she intends to sleep with and gets a considerable way down it before going on to other things.
In The Book of Tobit, it's not clear exactly how closely Tobias and Sarah are related, but their marriage is not only allowed but considered obligatory.
Eat and drink and be merry tonight, for no man is more entitled to marry my daughter Sarah than you, brother. Besides, not even I have the right to give her to anyone but you, because you are my closest relative.
Due to the nomadic, tribal lifestyles of the ancient Israelites, this is true throughout the Bible. Jacob married TWO of his cousins, the sisters Rachel and Leah, and also fathered children by their handmaidens.
Also due to the fact that, in the list of relatives and other people an Israelite man is not allowed to have sexual relations with, "cousin" is conspicuously absent.
In the young adult book How I Live Now by Meg Rosoff, teenage cousins Daisy and Edmond fall passionately in love. Daisy wonders uneasily for a while "if that's the feeling your supposed to have when your cousin touches a perfectly innocent part of your anatomy that's even fully clothed". By the middle of the book, she doesn't care. The book treats their romance sympathetically.
In Harry Potter, it's implied that purebloodism leads to frequent inbreeding. Arthur and Sirius explicitly state that all surviving pureblood wizards are related to some degrees. Particularly after the wholesale slaughter of the second Death Eater war, there are simply so few purebloods left that those who still care about blood purity will have no alternative but to marry their cousins.
Sirius and Regulus Black's parents, Orion and Walburga, were second cousins.
Teddy Lupin and Victoire Weasley are fourth cousins once removed.
Molly Prewett and Arthur Weasley were third cousins through the Black family even before they married.
Harry and Ginny are implied to be third cousins. The Black Family Tree includes as Dorea Black's husband Charlus Potter, whose information fits with him being James Potter's father.
After Tonks's Patronus takes a canine form, Harry wonders if she had been in love with Sirius, her cousin once removed, since he was an Animagus who turned into a dog. It turned out to be Lupin, a werewolf, however.
The Gaunt family is described as "An ancient, in-bred, pure-blood wizarding family living in slovenly conditions in a shack in Little Hangleton." This is supposedly the main cause of poor Merope's "cross-eyed" appearance.
The corrupt churchman Annias tries to persuade Queen Ehlana to marry her cousin, Prince Lycheas, in the David EddingsElenium trilogy. She refuses, mostly on the grounds that she can't stand him but also on the grounds that he might actually be her half-brother, given that her father and his mother were a little closer than siblings ought to be. He isn't. Lycheas was actually the son of Annias, which was part of why he was pushing the marriage.
In the King Arthur trilogy that begins with The Seeing Stone, the narrator is a medieval teenager (named Arthur) whose family circumstances parallel King Arthur's. He and his first cousin Grace are pretty much planning on a betrothal when they find out that Arthur's parents are really his foster parents and that he's actually the son of Grace's father by a peasant woman — so they're half-siblings, not cousins, and any thoughts of marriage have to be dismissed immediately. There's close and then there's too close.
In Christopher Moore's Fool, Pocket has running on/off affairs with both Goneril and Regan, unaware that they're both his first cousins by way of rape. Probably wouldn't have stopped any of them if they did know, though. He certainly doesn't seem horrified by it when he does find out. In fact he winds up marrying the youngest sister Cordelia. Whether she knows about the family connection or not isn't revealed.
Skinflick in Josh Bazell's Beat the Reaper is a young mafioso in love with his cousin. The narrator is non-judgmental about this.
In Tanya Huff's The Enchantment Emporium Gales, a clan of witches usually (though not always) marry their cousins to keep from diluting the magic inherent in their genes and to keep said magic secret. Furthermore because there are far more more female Gales than male the boys usually "make the rounds" of their age group cousins before settling down. This imbalance between the sexes also leads to a lot of "close" relationships between the Gale girls. One of these, between main character Alysha and her cousin Charlie is particularly focused on in the book.
In the novel Middlesex, the protagonist's parents were second cousins that eventually fell in love, but what they didn't know was that the father's parents were actually brother and sister, resulting in a rare recessive gene to make their child Calliope (later Cal) born intersexed.
In Jude the Obscure by Thomas Hardy, Jude and his cousin Sue fall in love. It's not a problem at all (unlike everything else in the world.)
Without spoiling the story, it's a pretty major problem. It's the reason they resist their attraction in the first place which causes so many problems down the line. Though the novel attempts to make the argument that the judgments and restrictions of society are worse than the actions of the characters.
In the Iliad Achilles and Patroclus are cousins. Whether or not they were kissing has long been a matter of debate.
An interesting twist is found in the Alfred, Lord Tennyson poem Lady Clare. The titular earl's daughter is engaged to her cousin, Lord Ronald, much to the delight of her nursemaid...who promptly reveals that Clare is actually her own daughter, whom she substituted for the real Lady Clare, who died in infancy. Ronald, as the next male-line heir, ought to be inheriting everything that Clare's father left to her. Clare, horrified that Ronald would be "kept from his due" and married to a peasant, leaves the castle only to run into a bewildered Ronald. She explains everything, and he shrugs it off and says they'll marry anyway, "and you will still be Lady Clare."
Tess of the d'Urbervilles is a rather tragic example. Tess' cousin Alec is pretty much obsessed with her and it leads to him raping and impregnating her, and her eventually murdering him. Though, as it turns out, his family merely took the d'Urbervilles name and they're not actually related at all.
Owlsight has a brief relationship between Darian and (adoptive) double first cousin Summerdance.
Illyria by Elizabeth Hand is about the romance between first cousins Maddy and Rogan, whose fathers are twins.
In Nerve by Dick Francis, the protagonist is hopelessly in love with his cousin. She spends much of the story discouraging the idea, though it turns out the feeling is mutual, and she's beginning to come around toward the end.
In the Nero Wolfe novel The Red Box, Nero deduces that one of the characters is interested in marrying his cousin. Ultimately, she is revealed as not actually being related.
In Charmed Life, by Diana Wynne Jones, Cat and Gwendolen's parents were first cousins. Chrestomanci explains that when they decided to marry, it caused their family to make a great fuss. "It is, you see, rather a bad thing for cousins to marry when there's witchcraft in the family."
In the Knight and Rogue Series Michael has a rather serious crush on Rosamund who is his second or third cousin (it never says the exact relation) and who, since they grew up together, sees him as a brother.
Within the Kencyr race of Chronicles of the Kencyrath, it's not uncommon for cousins to marry repeatedly to increase their Shanir gifts and the author has already indicated that the most likely partner for Jame will be her brother, Torisen. Then again, the Kencyr are also noted to have magical healing powers which seem to clear up some of the recessive disorders. Then again, some of the pureblooded families are also starting to experience some side effects such as one character's whose body repeatedly rejects his teeth so that they rot out of his gums and grow back constantly.
In the Montmaray Trilogy, both Sophie and her brother Toby are in love with their cousin, Simon. But neither of them knew he was their cousin when they fell in love with him, but both continue to engage in relations with him after finding out.
Camille and Thérèse in Thérèse Raquin, though their marriage didn't involve much, if any, sexual activity.
In the Bunduki novels by J.T. Edson, Bunduki and Dawn are adoptive cousins. They end up married.
Cersei sleeping with her cousin Lancel becomes a plot point, thanks to how sensitive that information is, with her being the king's widow (and how easy it is to manipulate Lancel if you're aware of it) and how jealous her incestuous twin brother is.
One of Ren's sisters would rather marry Cullen Moorland, but his mothers were sisters to their father; they are seen as full cousins, and with birth defects and inbreeding being major concerns in this world, especially among the nobility with its fears of being polluted by common blood, she is voted out.
Eldest Porter is revealed to be the child of people who are genetically full cousins, but socially considered to be siblings. She's healthy - the onus is on her parents for breaking taboo like that. It should be noted that in this world men are very rare, and a man marries every sister in a family; the sisters themselves are born of several different mothers.
Also it's mentioned that the girls's parents did seriously consider to have him marry one of the girls, "sighing because there was only one if him".
In the Lowlands Of Scotland series, Jamie McKie ends up married to both of his first cousins (not at the same time).
In UK children's author Malcolm Saville's Lone Pine series, first cousins Jon and Penny Warrender are engaged by the end of the final book.
In Warriors there are plenty of kissing cousins. And more. Lots more. Needless to say, the family tree is... complex.
In Andre Norton's Ice Crown, Nelis asks whether Roane is "ringed" to her first cousin Sandar, which causes Roane to laugh. Though at the end, he explains that he is the queen's first cousin, to show that their connection is not romantic.
In The Darkangel Trilogy there's a love triangle in which all three participants are cousins. Two of them didn't know they were related at first, but the discovery has no effect at all on their romance either bad or good - it doesn't seem to be relevant to them.
Seraphina: Staying true to the Western European feel of the setting, first cousins Prince Lucian and Princess Glisselda of Goredd are engaged.
In Dorothy L. Sayers's Busman's Honeymoon, Lord Peter Wimsey worries about children because of how his brother's turned out. Harriet points out that his brother married his own cousin; his sister, who married a commoner, has children who are perfectly fine.
In Un grito en las tinieblas; la vida de Zárate Arkham, the titular character sleeps with her cousin, although both of them were possessed by the spirits of their uncle and his female servant respectively –which make the sex scene a case of double incest.
Rand al'Thor is worried about this when he considers courting the Andoran Daughter-Heir Elayne Trakand in The Wheel of Time after he learns that he is descended from Andoran royalty on his mother's side, making them distant cousins. He is reassured after an expert on genealogy informs him that if they were both commoners, they wouldn't be considered related.
In Thai Literature Phra Apaimanee, Sin Samut and Arunratsamee are first cousin.
In Making Money, marrying cousins is mentioned as traditional for the Lavishes in order to keep the money in the family, although "occasionally they married outsiders to avoid the whole 'three-thumbs' situation."
Played with in The Hunger Games. The Capitol does not approve of Katniss' close friendship with Gale, seeing him as a potential rival to Peeta, so they claim the two are cousins. In the third book President Coin asks Katniss if she wants Gale declared as her new lover, which would make them this trope in the public's eye. Katniss declines.
The Reynard Cycle: Two of the suggested brides for King Lionel are his cousins by his aunt. No one raises any objections over this.
Live Action TV
An episode of Just Shoot Me! involved Nina being pursued by a handsome man who, for some unfathomable reason, she has no attraction to. When he mentions he is also from Colby, Kansas, they discover they are cousins. He's completely disgusted and flees, while Nina is relieved that she's not stopped being attracted to men.
Arrested Development had a recurring storyline about George-Michael's crush on his cousin Maeby who eventually turns out not to be his biological cousin). Furthermore, when these feelings become mutual, Maeby tries to hide from them by dating a boy from her school, who turns out to also be her cousin. Again, not by blood. This was mirrored in two storylines in the final season. The first saw Michael Bluth (played by Jason Bateman) thinking that a prostitute was his long-lost sister and hiring her to work at the company; she thought this was a Pretty Woman situation and started coming on to him. (The prostitute was played by Justine Bateman, who is Jason Bateman's real-life sister.) Then, in the final episode it was revealed that Lindsay was not actually Michael's biological sister. Upon finding out, she decided to act on a crush she had had for years. Additionally, Michael ended up going out with a woman who suffered from mental retardation on account of her parents being cousins. It was a lot funnier and less creepy than this sounds.
Relatively common in Hispanic Soap Operas. During Venezuelan soap Carita Pintada's pre-premiering the author claimed that the main couple could achieve a happy ending with white wedding and all because they were only third or second grade cousins, coincidentally the closest blood relation allowed to marry according to actual laws.
For the most (emphasis there) part in Latin America, people consider cousin relationship to be rather incestuous only if they are first cousins, second cousins and onwards are not subject to this taboo.
Jonathan and Tammy were a popular couple on Guiding Light. However, the first time they slept together Tammy had no idea they were cousins and Jonathan was using her for revenge on his mother. When she did find out, she was angry at him for a long time. (About a couple weeks.)
This is not uncommon in Soap Operas in general, given the frequency of "true parentage is revealed" storylines that can make previous non-relatives with crushes on each other into cousins. For example, Cassie DiMera and Shawn Brady on Days of Our Lives.
Then there are people who skirt the edges of this trope by dating their half-siblings' cousins on the other side...
In the HBO series Dream On, Martin and his cousin (played by Helen "Supergirl" Slater) briefly undergo a bout of frustrated desire for each other, which only dies when they notice, when they finally get the time and privacy to indulge themselves, that their feet are too similar.
Marc: She's your cousin!? Are you cousins? I didn't know that! Wow! I have something I want to say but this will put us off the air!
30 Rock has this when Liz Lemon meets a guy that seems perfect for her. At least, until they go back to his place and she notices a picture of her great aunt. They do the math and figure they are third cousins (i.e. sharing a great-great-grandparent). There's a discussion on how closely related they could be without it being creepy. He says fifth cousins. She says never.
In season two of Game of Thrones, while Jaime is captured by the Starks, Cersei ends up sleeping with her cousin Lancel because he reminds her of Jaime. Also, like in the books, Tywin Lannister married his cousin Joanna, who died giving birth to Tyrion.
In a 3rd Rock From The Sun episode, the aliens went to the family reunion of a family with the last name "Solomon", pretending to be long-lost relatives. Tommy fell in love with his "cousin" and Hilarity Ensued.
Bo Duke: Daisy Duke, if you wasn't my cousin, I'd marry you! Daisy Duke: Never stopped anybody in this family before.
George dated his cousin in an episode of Seinfeld in an attempt to get his parents mad after they started neglecting him.
On The George Lopez Show, Max gets a major crush on his attractive cousin. George made jokes about their mutant offspring (since Max by himself is already dyslexic) to discourage that. The cousin milks him for all he's worth by having him do all her chores.
On the Gilmore Girls, Lorelai (and later Rory) is horrified to discover that her paternal grandparents were second cousins. Emily doesn't think it's a big deal, since that was common among upper class family in those days.
The Nanny had an episode titled "Kissing Cousins" where Fran starts to date a Jewish doctor (played by Jon Stewart) who she thinks is perfect for her. They then meet up at a wedding in their temple, where Fran's mom declares, "Oh, I see you have met your cousin!" This makes them squick and they stop dating; however it is mentioned again in later episodes.
In an episode of Friends, Ross and Monica's female cousin comes to visit for the wedding, and ends up staying at Ross' apartment. After a slo-motion Hair Flip, Ross finds he is attracted to her and decides that she is attracted to him too, leading him to try and make a move... Hilarity Ensues.
In one episode of How I Met Your Mother, Ted, Barney and Robin go to a club. Barney grinds on this girl all night before she turns around and he realizes it's his cousin Leslie.
In Chouriki Sentai Ohranger, Kaiser Buldont and Princess Multiwa wed in episode 41 and have a child near the end. It's okay because they're robots.
In the Don't Trust the B---- in Apartment 23 season 2 episode "Original Bitch…", Mark tells June that he left a voicemail on her answering machine. June tells him she didn't get the voicemail because Chloe wouldn't give her the code. The conversation afterwards:
June: She [Chloe] won't tell me anything she cares about!
Mark: She might just a private person. I mean, I was like that when we first met.
June: The first day we worked together, you told me you boned down on your cousin 'cause you didn't want to go to college a virgin.
Married... with Children: Everyone is family in Wanker County, which came as a surprise to Kelly. Apparently she was a little too "friendly" with one of her relatives; how friendly is unknown, but considering it's Kelly...
The Frasier episode "Beware of Greeks" features a very one-sided version between Niles and Cousin Yvonne, who apparently makes a beeline for him whenever they're at a family gathering.
Frasier: A distant cousin who has a slight crush on Niles.
Niles: "A slight crush?" There are cannibals who are less man-hungry.
The second verse of Weird Al'sAvril Lavigne parody "A Complicated Song" has the protagonist alone with his girlfriend for the first time, presumably about to engage in a little Angry White Boy Polka, when:
Discussed by Eddie Izzard, in regards to the British royal family:
She was one of our more frumpy queens. They're all frumpy, aren't they? Because it's a bad idea when cousins marry! (...) First rule of genetics: spread the genes apart, you know? But the royals are just obsessed with: "Are you a royal family? Are you a royal member? Well, then you can marry me, 'cause you're the same gene pool and our IQ's will go down the toilet." Fantastic. That's why there's no crazy royals, they're all kind of: (drawls) "Hello, hello. What do you do? Oh, you're a plumber. What on earth is that?"
"If you go to family reunions hoping to pick up girls..."
In Antigone, the eponymous character is engaged to her cousin Haemon. Haemon's father Creon and Antigone's mother Jocasta are brother and sister. It's worth mentioning that he is also her first cousin once removed since Antigone's father is a son of Jocasta's. Coming from that family, marrying a cousin must've seemed positively conservative.
At the end of The Importance of Being Earnest, The Reveal that frees Jack/Ernest to marry Gwendolen also makes them first cousins. This isn't specifically addressed, but he does start referring to her mother as his aunt, so at least they're aware of it.
In 1879, Cyrano and Roxanne from Cyrano de Bergerac are cousins. Although they don't actually end up together, their familial connection is never presented as squicky or an obstacle in their relationship. Given Catholic rules on consanguity this probably means 'cousin' was more a courtesy then genetic relationship.
In most of the productions anyway. In Hungary it's less "he wishes his cousin returned his romantic love for her" and more "he's so obsessed with her that he thinks all men, including himself, are unworthy of her". There's still some weirdness going on there, though.
And technically speaking, Romeo and Juliet themselves are at least distant cousins. Laertes's own father was a Capulet man who abandoned him and his prostitute mother, and a good part of Laertes's reason to become a Self-Made Manand exterminate the Capulets was revenge against his dad.
In Brighton Beach Memoirs, Eugene has somewhat of a crush on his cousin Nora. However, it's not romantic so much as that he's entering puberty and there's a beautiful girl in the house. His older brother Stanley has a similar attraction to her.
Subverted in August: Osage County. Ivy is in a relationship with her cousin Little Charles, which is already considered pretty bad by the others. Then it's revealed that Little Charles is actually the biological son of Beverly, Ivy's father, making the two brotherand sister as well.
As an extension for its love of the sibling versionFire Emblem has plenty of this, several preexisting relationships in 4s 2nd generation take on this form, and by selective pairing of characters in the first generation it is possible to make a vast number of such pairings.
Two particularly noteworthy incidents in FE4's second generation are the predestined couples of Lana/Faval and Lester/Patty. Because their mothers Aideen and Briggid were identical twins, IS pulled off the impressive feat of doing this and Brother-Sister Incest at the same time.
It is possible to make Roy and Lilina from the 6th game cousins... by pairing Eliwood with the Pegasus Knight Fiora and Hector with either of Fiora's youngest sisters Florina or Farina in the 7th game (which is a prequel to 6). Since 7 was not released yet (and the pairings involved exist among other possible pairings), the 6th game never makes any mention of the possibility.
Fire Emblem Awakening uses a love system very similar to that of the fourth game. Either Lucina or a Chrom-fathered Cynthia or Kjelle can potentially marry their paternal cross cousin Owain while other cousin pairings can be set up with certain combinations of parents. The international release has the status screens of such a pairing Bowdlerized to read "Companion" instead of husband/wife, though. A female Morgan mothered by Lissa can also marry her cousin Inigo or Brady.
An ill-fated romance between two Kissing Cousins forms part of the plot of the adventure game The Dark Eye.
Though nothing ever comes of it, Brother in Final Fantasy X-2 has a noticeable (and one-sided) crush on Yuna. Brother's father and Yuna's mother were siblings.
It should be noted that in The Sims 2 and The Sims 3, the game does not even allow the option for first cousins to be married. (A certain cheat will allow them to have offspring, if the player so chooses). However, more distantly related Sims have the ability to seek romantic interactions with one another (probably because the family tree in the game does not recognize first cousins once removed and beyond, or great-grandparents for that matter).
At the end of Persona 4, your little cousin Nanako tells you that she wants to marry you when she grows up, and apparently won't take "no" for an answer. If you didn't max the link, her father won't allow it. If you did, he's gonna hold you to it.
In Bully, the Preppies are the kids of a bunch of inbred rich people. When Gary gets them to attack you with his old trick of insulting them and saying you did it, the "inbred" insult is met with indignation and the phrase "And first cousins is legal anyway!"
In Jade Empire, it's revealed that Dawn Star is the long lost daughter of Sun Li, the brother of the Emperor. As a result, when a male protagonist forms a ménage à trois with the Princess Silk Fox and Dawn Star, the two ladies are in this kind of relationship.
In Matches And Matrimony, this is one of the nine paths which the player character can take, if she accepts (or is too weak-willed to refuse) the proposal of her cousin Mr. Collins.
BlazBlue: While there are no examples given, the Yayoi family (Tsubaki's family) practices this; they are so obsessed with blood purity that marrying in the family is the only choice they get. Which has led to the family being Royally Screwed Up; Tsu's the only surviving heir to the family
A lot of visual novels will often feature a cousin as an option. Whether or not the main character ends up in a relationship with her (or him) depends on the player's choices.
While he's joking for the most part, Umineko: When They Cry's Battler Ushiromiya is not adverse to playing grab-ass with his first cousin Jessica. As for more serious cousin-cousin relationships, the second half of the story reveals that Sayo Yasuda (who is implied and later confirmed to be Shannon, Kanon, and Beatrice) is involved with as many as three of his/her cousins. Who are also his/her niece/nephews (since Kinzō is both Sayo's father andgrandfather). As it turns out, this is a large part of Sayo's issues, since finding out that s/he's actually related to his/her love interests makes him/her think of him/herself as disgusting and no better than Kinzo.
The entire Nanaya clan from Tsukihime, with the exception of Shiki due to his situation. They only breed within the clan to sustain and increase the psychic power within their bloodline.
Referred to in Dead Days. Brown-hair claimed he knew everything, so Blondie tested him out. Brown then stated Blondie's first kiss was with a cousin at a family reunion. His name was Steve.
Tedd of El Goonish Shive averts this trope, being almost allergic to the idea of his "ugly cousin" Nanase as a sexual being at all. (Said cousin is, of course, scorchingly hot actually, as Tedd admits much later.)
In Templar Arizona, Mose's grandfather want him to "keep the bloodline pure" and tries to browbeat him into taking up with the temple dancers. Mose objects on the grounds that they're his cousins ... and underage.
Trigger Star: Saeurkraut and Avacado's idol, Exlax The Mighty. Not only are they cousins, they were lovers.
In Scandinavia and the World, Norway and his cousin, Jan Mayen, actually get in trouble for being in a relationship, resulting in the latter's execution.
HomeSchooled: Juan the gardener has an infatuation with Dulce the housekeeper, despite the fact that they're 2nd cousins. This disgusts her to no end.
In Monster Buster Club, Cathy's big secret is that she kissed her cousin Elton, but only on the cheek, and only on a dare.
Wolverine and the X-Men made Silver Samurai and Mariko Yashida into husband and wife, even though they're cousins in the comics. It's not mentioned one way or another if they're still related in the cartoon. Justified as they're Japanese and it fits their culture.
When Hervé and Nicolas follow the gang to the factory in an episode of Code Lyoko, Odd and Aelita pretend to have sneaked out of school on a date, despite the fact that Aelita joined the school under the pretense of being Odd's first cousin. Note that it works as a perfect in-universe Fridge Brilliance: it was Fake-Out Make-Out, but Hervé and Nicolas probably reads it: "They are kissing? But... They are cousins! Oh... No wonder they are hiding." Notably, when Hervé report the fact to Sissi, she obviously doesn't believe him and finds the concept absurd.
Scooby-Doo and one of his cousins were attracted to one of their cousins, Scooby-Dee. It's less Squicky since they're dogs, and inbreeding is typical.