History Main / HalfIdenticalTwins

* The official medical terms for these kinds of births are sesquizygous twins or semi-identical. They are incredibly rare. Of the theoretical 100 billion humans ever born, less than a thousand pairs -- 0.00000002% of all humanity -- are thought to be born like this. In modern recorded times, depending on how strict one categorizes amniotic genotyping, less than five proposed and [[https://www.nejm.org/doi/full/10.1056/NEJMoa1701313 only two]] medically confirmed.

It's common -- especially in drawn or animated media, where the creator has complete control over the appearance of the characters -- to use brother-sister twins as being each other's DistaffCounterpart and SpearCounterpart. They often display identical twin tropes, such as TwinTelepathy or {{Synchronization}} -- ''especially if they are CreepyTwins.'' It's a way to make sure that twins, even if they're not identical, [[CastSpeciation are immediately identifiable as such]] if it's relevant to their characters, and there are no other visual cues to show that siblings are fraternal-twins instead of just regular brothers and sisters. If the two siblings drift apart at any point during the story, a TwinDesynch is likely, and often occurs at puberty when the secondary sexual characteristics start becoming more apparent. In fact, if they ''don't'' desynch to some degree during puberty, they're likely to come across as a little ''[[{{Twincest}} too]]'' close.

[[folder:Web Videos]].

* While extremely rare (only three to five known cases), there are cases in which otherwise identical twins can be of the opposite sex. [[http://en.wikipedia.org/wiki/Twin#Semi-identical_twins More info here]] from Wiki/TheOtherWiki.

Compare to the rare real-life phenomenon of [[http://news.bbc.co.uk/2/hi/6498215.stm semi-identical twins]], where the twins have identical genes from their mother and different genes from their father, and thus can be the same sex or opposite sexes. This could lead to an UncannyFamilyResemblance if the sperm are similar enough.

* The Beauvoi twins, Reynard and Hermione, from ''Fanfic/BeCareful'' are described as this, with Reynard being referred to by Lord Voldemort in one side-story as looking like a male version of Hermione, which is particularly notable given that their canon counterparts, Hermione Granger and [[spoiler: Draco Malfoy]] are not related and bear no resemblance to one another at all.

** Tragically TruthInTelevision; there was apparently a real rash of this kind of thing back in the 70s, when cutting edge thinkers had decided that gender was just a matter of socialization. Turns out it's a little more complicated than that. See Wiki/{{Wikipedia}}: [[http://en.wikipedia.org/wiki/David_Reimer David Reimer]]. It happened more than once because the first doctor, [[http://en.wikipedia.org/wiki/John_Money John Money]], who performed it wrote medical articles stating that the procedure went well without aftereffects, because he didn't like the results he got -- they conflicted with his theory.

* ''WesternAnimation/TheSimpsons'': The twins from Audrey McConnell's 4th grade class at Springefield elementary. The twins consist of one boy and one girl.

* The ''WesternAnimation/{{Animaniacs}}'' fan series ''WebAnimation/ZanyToTheMax'' has Zak Warner and his sister, Ko. Taken UpToEleven by [[ConjoinedTwins conjoining them]].

* Taken UpToEleven with ''Literature/{{Redwall}}'''s Marlfoxes, a family of ''seven'' siblings (who may or may not be actual septuplets, given that they're foxes and could be one big litter) described as all looking almost identical.

* A rare {{Justified}} example occurs in ''VideoGame/TellMeWhy'': Alyson and Tyler were both assigned female at birth and are actually genetically identical, but Tyler is a trans man while Alyson is a cisgender woman.

* Played totally straight in ''Ladykiller in a Bind'' where the plot revolves around the fact that The Beast can easily impersonate her brother by simply wearing a suit.

* ''WesternAnimation/TheOwlHouse'' has [[Characters/TheOwlHouseAmityBlight Amity Blight]]'s elder siblings Edric and Emira. Emira wears earrings and has longer hair, with a tamer fringe compared to Edric's messier quiff, but beyond that, they're essentially identical. They appear to consciously coordinate their outfits outside of school: their clothes come in identical colors, and either identical cuts or very similar styles with only minor gender differences. And since they're in the same [[ColorCodedWizardry magical track at school]], their uniforms there are identical too.

* ''Literature/PleaseDontTellMyParentsImQuenOfTheDead'' Chris and Annie are the same height and have the same "[[BigRedDevil scarlet red skin]] and glossy black hair", although his muscles, her breasts, and the different lines in their faces distinguish them.

* Ser Jaime and Queen Cersei Lannister of ''Literature/ASongOfIceAndFire''. As kids, they looked so much alike that they would sometimes wear each other's clothes and swap places for a day without anyone suspecting. The fact that their parents were cousins might have helped. They're also {{Twincest}}uous (with the implication that the narcissistic Cersei sees it as the closest she can get to ScrewYourself). When Jaime starts to grow a beard while spending time as a prisoner in the third book, he thinks to himself that Cersei will hate that it makes them look less alike, and it becomes a very important symbol of their growing distance.

* Ser Jaime and Queen Cersei Lannister of ''Literature/ASongOfIceAndFire''. As kids, they looked so much alike that they would wear each other's clothes. The fact that their parents were cousins might have helped. They're also {{Twincest}}uous (with the implication that the narcissistic Cersei sees it as the closest she can get to ScrewYourself). When Jaime starts to grow a beard while spending time as a prisoner in the third book, he thinks to himself that Cersei will hate that it makes them look less alike, and it becomes a very important symbol of their growing distance.

* As children, Thom and Alanna, of Creator/TamoraPierce's ''Literature/SongOfTheLioness'' series, were so much alike in face and body shape as to be mistaken for each other, if dressed alike, which they exploit so Alanna can train for a knight and Thom can be a mage. The only distinguishing feature of the twins at that time was the length of their hair. It stops applying once they're grown, as Alanna comments that Thom has grown taller than she when they meet as older teenagers.

* Johan and Anna/Nina from ''Manga/{{Monster}}'', [[spoiler:who were dressed identically when children and were almost indistinguishable. It remains when they grow up, to the point that Johan [[CreepyCrossdresser disguises himself as a woman to hide]], and when Nina arrives in the same town she's confused for her brother's female identity]].

* ''Series/PowerRangersRPM'' has the peppy twin geniuses Gem and Gemma. They have several superficial differences if you look close enough, but you have to look ''very'' closely - not because the differences are minor, because they aren't, but because the twins in question are ''just that [[SingleMindedTwins single-minded]]''.

** The short lived FOX series ''Series/{{Mental}}'' had the part about a botched circumcision resulting in a sex change. It was all fine, until the "girl" ended up lighting him/herself on fire for no apparent reason and kept seeing him/herself in the mirror without a face. The protagonist (a rebellious psychiatrist) realized what was going on. The "girl's" true identity as a male was trying to push its way to the surface. "She" didn't even have proper female genitalia, just a prosthetic designed to look like one. The crackpot who convinced her father to do this planned to give "her" a vagina when "she" was 18. (Because [[SarcasmMode every girl]] waits until she's 18 before having sex or having ADateWithRosiePalms, and wouldn't notice the difference because NoPeriodsPeriod is normal.) Naturally, when "her" boyfriend finds out the truth, he runs away in disgust. At the end, "she" gets a boyish haircut and decides to try to explore the male lifestyle, even though, without certain body parts, the experience would be far from complete.
* ButchLesbian "Walter" from German series ''Series/HinterGitternDerFrauenknast'' ("''Behind Bars - the Women's Prison''") has a twin brother who's apparently indistinguishable from her without his beard. They use this in one episode to change roles, allowing her to escape and him to get closer to several female prisoners.
* ''Series/TheBigBangTheory'' averts this by giving Sheldon a fraternal twin sister, Missy, who could pass for a sister but is not simply him with a wig. Sheldon explains the scientific errors behind this trope in his typical SesquipedalianLoquaciousness. [[CasanovaWannabe Howard]] replies, "Hallelujah!" as Missy is rather attractive and Sheldon is rather gaunt.
* Also averted on ''Series/TheEdisonTwins'': Annie is a redhead, while her twin Tom is blonde. (There was even an episode in which they explained the concept of fraternal vs. identical twins.) Meanwhile, their younger brother Paul is a brunette!

* In '' Series/RavensHome'', Nia mentions that her hairstyle is the only thing that separates her from her twin brother. Of course their actors [[AllegedLookalikes don't look similar]], though Nia could also have been joking.

* In ''Podcast/TheAdventureZone'', [[spoiler:Lup]] is revealed to be [[spoiler:Taako]]'s twin sister. Justified in that [[spoiler:Lup]] is trans, and her and her brother's general ambivalence to gendered fashions make their wardrobes very similar.

* OlderThanSteam: See Sebastian and Viola from Creator/WilliamShakespeare's ''Theatre/TwelfthNight''. Viola, assuming her brother is dead, disguises herself as a man -- so when the actually-not-dead Sebastian returns, he promptly gets mistaken for his "sister". This could be seen as reflecting Shakespeare’s life as the father of opposite sex twins, Hamnet and Judith; Hamnet died in childhood.
* Siegmund and Sieglinde from ''Theatre/DieWalkuere''.

** Coricopat and Tantomile from ''Theatre/{{Cats}}''.

* Vent and Aile in ''VideoGame/MegaManZX'' seem to be like this... That, or they're just [[SchroedingersPlayerCharacter two versions of the same person]]. It depends on where you look.
* Likewise, games in the ''VideoGame/SuperRobotWars'' series often give you a choice for the OriginalGeneration Player Character, and when those series get adapted to the ''VideoGame/SuperRobotWarsOriginalGeneration'' sub-series, the different choices often undergo some form of DivergentCharacterEvolution and become their own characters. But in the case of Raul and Fiona Gureden of ''VideoGame/SuperRobotWarsReversal'' and Akimi Akatsuki of ''VideoGame/SuperRobotWarsGC'' they were presented as a Male/Female choice of the same person. The OG games made them twins, and in Akimi's case, the sister was renamed "Akemi". Averted however with Ingram Plisken and Viletta Vadim of ''Super Hero Sakusen'': they were male and female versions of the same character, but when introduced into ''VideoGame/SuperRobotWarsAlpha'' and ''Original Generation'', they became [[spoiler:{{Opposite Sex Clone}}s]].
* ''Franchise/FinalFantasy'':
** Palom and Porom from ''VideoGame/FinalFantasyIV'' qualify as this. The original sprites lacked sufficient detail to make it clear whether they were meant to be identical or simply share a number of similar traits and style of dress; but the CG renders in the DS edition depict them as having identical facial features.
*** However, instead of being clones of one another, the two are characterized with distinct themes of reversal and mirror imagery. Not only the sexes, but elements of personality (Palom is boastful and rude, Porom reserved and polite), their style of dress (both are pictured wearing red and green outfits with identical patterns, but one's is red where the other's is green, and vice versa), their use of magic (Palom uses the destructive Black Magic, Porom uses the healing/supportive White Magic), and hairstyle (the sprites show a right/left reversal between the two, otherwise being identical; the portraits show Porom's hair looking well-groomed and Palom's hair looking rather messy).
*** By the time that ''VideoGame/FinalFantasyIVTheAfterYears'' rolls around, they've developed their own styles and no longer dress in complimentary outfits. They've also dyed their hair different colors (Porom's hair is now a vivid pink, whereas Palom has white-tipped bangs), which makes them look even less alike. However, they still have identical facial features and the CG renders depict them as being the exact same height even as adults, so they never manage to escape this trope completely.
** Alphinaud and Alisaie from ''VideoGame/FinalFantasyXIV'' are this in terms of looks, but their personalities are so different that Alphinaud serves as a major character throughout the main plot, whilst Alisaie leaves soon after her introduction and is only important in the plot for the Binding Coil of Bahamut raid. Humorously, Alphinaud (the male twin) is [[RunningGag frequently]] [[DudeLooksLikeALady mistaken]] for Alisaie (the female twin), but not the other way around... at least until the first expansion, where she's shown a few times spying on the Warriors of Darkness and eventually returns to the main plot ([[OldSaveBonus with slightly different dialogue depending on whether you did the Coil or not]]) and becomes instrumental to their defeat. By the time the second expansion rolls around she's just as much part of the main cast as her brother. Patch 5.5 reveals that this is a BerserkButton for Alisaie [[spoiler:when she rips Estinien a new one when he mistakes her for her brother showering praise to her. It's the hair ruffle that really pisses her off.]]
* In ''VideoGame/TheLastBlade 2'', a woman impersonates her dead twin brother, Kojiroh, a member of the Shinsengumi, in order to bring his killer to justice. She ends up living the rest of her life under the charade, taking on her brother's identity as a tribute to him.
* Alfred and Alexia in ''VideoGame/ResidentEvilCodeVeronica''. In fact, the resemblance is so good that Alfred is able to convincingly pretend to be Alexia for several ''years'' after she was [[HumanPopsicle frozen]] in order to make people think she was still alive. Kind of explained in that [[spoiler:they are really clones.]]

* Tate and Liza, twin Gym Leaders in ''VideoGame/PokemonRubyAndSapphire''. They look so similar that it's a common mistake to think [[ViewerGenderConfusion Tate is also a girl]], thus making them fully identical.

* Averted in ''VideoGame/EagleEyeMysteries'' with the title protagonists, Jake and Jennifer Eagle. Besides the obvious gender differences, he's a redhead and she's brown-haired.

* Subverted in ''VideoGame/BioShockInfinite''. Robert and Rosalind Lutece seem to be this at first, though this is the ''least'' abnormal trait they display. They actually turn out to be [[spoiler:different versions of the same person from parallel universes]].
* In the ''Manga/{{Bleach}}'' video game ''The Third Phantom'', we have the main protagonists Matsuri and Fujimaru Kudo, both have similar hair and eye colors and both are noted to have similarly enormous talent and spiritual pressure.
* Reynold and Wren from ''VideoGame/CostumeQuest''. The player chooses which one they want to play, the only real difference between the two being gender, and saves the one that they didn't choose.
* Isabelle and Digby from the ''VideoGame/AnimalCrossing'' series look similar besides fur color and clothing. In ''[[VideoGame/AnimalCrossingHappyHomeDesigner Happy Home Designer]]'', Digby insists on being called a twin brother, not a little brother.
* Prince Alaric and Princess Alana, in ''VideoGame/CuteKnightKingdom''. [[spoiler:They're so identical that for a long time, they're able to get away with pretending to be a single individual called Al. The observant player, however, will note that their eyes are different colors.]]
* In ''VideoGame/OdinSphere'', we have playable protagonist Velvet and her twin brother Ingway. While not exactly alike, both have similar features, share hair and eye colors, and have a tendency to wear rather {{Stripperiffic}} clothing.
* ''VideoGame/MassEffectAndromeda'': The protagonist is established in the character creation screen as one of a set of opposite-sex fraternal twins, and the character model for your twin uses the same settings you have, only gender-inverted.
* ''VideoGame/AssassinsCreedSyndicate'': Jacob and Evie Frye, who have enough similar features that people easily identify them as twins. It's a bit more of an InformedAttribute though, as while Henry describes them as being equal in height and have matching dark hair, Jacob's hair is darker and he's visibly quite a bit taller, and looks older thanks to a crooked nose (as he's more prone to fighting) and unshaven facial hair. They have enough similarities that you can tell they were ''probably'' this when they were younger, but the two went through significant DivergentCharacterEvolution as they got older thanks to Jacob's roguish behaviour and Evie's scholarly pursuits.
** ''VideoGame/AssassinsCreedOdyssey'' plays this a bit straighter with its optional protagonists, Alexios and Kassandra, both of whom look pretty much identical save for the former having a squarer jaw and being unshaven. Ironically, they're not even twins; one was a young child when the other was born (the older sibling is whichever one the player chooses to play), but they have such strong family resemblance and are close enough in age anyway one could easily pass for the other's Distaff or Spear Counterpart (which is kind of the point of the choice).
* Tsukino and Yosuke in ''VideoGame/{{Judgment}}'', to the point that Yagami tries to have Yosuke go undercover as his twin in order to catch a groper. Yosuke refuses, but the groper still mistakes him for Tsukino in the end.
* Aether and Lumine of ''VideoGame/GenshinImpact'' are a pair of twin {{Dimensional Traveler}}s. The twin that the player does not choose as their avatar gets captured by one of the gods of the world they just arrived in, with the other twin having their dimensional powers stripped from them, and going on a journey to rescue their twin.
* ''VideoGame/DragonQuestV'': Parry and Madchen, the hero's blonde children. Parry is mainly a physical attacker whereas Madchen is the magic powerhouse. Also, for whatever reason, Parry is the only who can wield the Zenithian Sword, even though both children are descendant of ''VideoGame/DragonQuestIV'''s legendary hero Solo/Sofia.

* Played completely straight with the BrotherSisterTeam of [[https://static.tvtropes.org/pmwiki/pub/images/kaname.PNG Kaname]] and [[https://static.tvtropes.org/pmwiki/pub/images/saori_8.PNG Saori]] Shishido from ''[[VisualNovel/ShallWeDateNinjaShadow Shall We Date?: Ninja Shadow]]''. It's even a huge plot point since Kaname is killed off almost at the start of the game and Saori pulls a SweetPollyOliver to join a group of vigilante that he was supposed to become a part of, needing just an ImportantHaircut and putting on male clothes to pass as Kaname.

* ''WebAnimation/DSBTInsaniT'': Killer and Killdra, who are both sarcastic goths who wear orange.

* Walky and Sal in ''[[Webcomic/WalkyVerse It's Walky!]]'', but less so in ''Joyce and Walky,'' and not at all in ''Webcomic/DumbingOfAge''. This is due to ArtEvolution, with the fact that they do have differences (in particular, Sal claims ParentalFavoritism for Walky because he "came out more white" while she has naturally kinky hair) being a point of contention between them. However, it might be there on ''some'' level, as Walky has mentioned that he's been mistaken for Sal before.

%%* ''Webcomic/TheAdventuresOfWiglafAndMordred'': Janus and Arthur, as illustrated [[http://liliy.net/wam/2008/05/09/seeing-double/ here]].
* ''Webcomic/{{Drowtales}}'': Kau and Shala, seen briefly [[http://www.drowtales.com/mainarchive.php?order=chapters&id=1037 as children]] where the only visual differences between them are different shades of blue for their eyes, Shala (the girl) having more prominent eyelashes and Kau (the boy) having spikier hair tied on the other side. This is averted after the timeskip where there are a number of obvious differences between them, the main one being that following usual drow sexual dimorphism Shala is noticeably taller than her brother, and after chapter 46 Kau gains [[RedEyesTakeWarning tainted red eyes]], [[spoiler:but Shala only lives a few minutes after this happens anyway]].

* ''Webcomic/{{Catena}}'': The littermates Bear and Bryony don't act alike, but except for their hair and Bear's chin they're pretty nearly identical. Their other sister Patches, on describing Bryony, even comments to Bear that "She looks like you, only, you know, pretty."
* Sam and April of ''[[http://www.drunkduck.com/dragon_city/ Dragon City]]'' look identical aside from gender and April's glasses; but according to the FourthWallMailSlot they actually are identical. This is because gender in dragons is influenced by incubation temperature (as in crocodiles) rather than genes. Every other set of twins in the comic are obviously fraternal, even having differently colored scales.
* In ''Webcomic/QuestionableContent'', people think that Claire and Clinton are this, but she's a couple years older than him. [[spoiler:It also doesn't work because Claire's actually trans, so she was presumably raised as a male.]]

* Ember and their sister Ariel in ''Webcomic/{{Blindsprings}}'', with the variation that Ember is non-binary in gender identity, but was assigned male at birth. The only real visual difference is Ariel having longer hair.
* In ''Webcomic/WelcomeToRoom305'', there was a rumor around his campus that Yoongsung was a crossdresser. They really were seeing his twin sister, Yoona. Yoona's hair color is lighter but otherwise they look very similar.
* ''Webcomic/TigerTiger'' is about the noblewoman Ludovica takes the identity of her twin brother Remy in order to seek adventure and pursue her dream of studying sea sponges. Sure enough, the siblings look similar enough for her to pull off the charade, though they are actually drawn in subtly different ways, such as in the shape of their jaw. The most obvious difference is how Remy's beauty mark is by his eye while Ludo's is at the edge of her lip.
* ''Webcomic/{{Hooky}}'' features the twins Daniella and Dorian Whytte. As twelve-year-olds, they look alike except for their hairstyles and [[CoordinatedClothes different - although matching - clothes]], to the point that a major plot point in the first part of the webcomic is the question of which of them is featured in an important prophecy.

%%* Fisk and Lucy from ''Webcomic/{{Better Days}}''.
* Pince Rayburn and Princess Hoya from ''Webcomic/ImStanningThePrince'' look almost completely identical except for Hoya's longer hair, make-up and dimples.

** As of 2011 there are now [[http://www.boston.com/lifestyle/family/articles/2011/12/11/led_by_the_child_who_simply_knew/?page=full news stories]] about a pair of teenage identical twins where one is trans.

* Tuffnut and Ruffnut Thorston from the film adaptation of ''WesternAnimation/HowToTrainYourDragon''.

* Both sets of ''Literature/TheBobbseyTwins'' are explicitly stated to bear a close physical resemblance to each other. Nan and Bert are both tall, dark-haired and slender, while Flossy and Freddie are small, blonde and chubby.

* ''Series/PowerRangersRPM'' has the peppy twin geniuses Gem and Gemma. They have several superficial differences if you look close enough, but you have to look ''very'' close- not because the differences are minor, because they aren't, but because the twins in question are ''just that [[SingleMindedTwins single-minded]]''.

** Tragically TruthInTelevision there was apparently a real rash of this kind of thing back in the 70s, when cutting edge thinkers had decided that gender was just a matter of socialization. Turns out it's a little more complicated than that. See Wiki/{{Wikipedia}}: [[http://en.wikipedia.org/wiki/David_Reimer David Reimer]]. It happened more than once because the first doctor, [[http://en.wikipedia.org/wiki/John_Money John Money]], who performed it wrote medical articles stating that the procedure went well without aftereffects, because he didn't like the results he got -- they conflicted with his theory.

* OlderThanSteam: See Sebastian and Viola from Creator/WilliamShakespeare's ''Theatre/TwelfthNight''. Viola, assuming her brother is dead, disguises herself as a man -- so when the actually-not-dead Sebastian returns, he promptly gets mistaken for his "sister". This could be seen as reflecting Shakespeare’s life as the father of opposite sex twins, one of whom died as a child.

* ''VideoGame/EagleEyeMysteries'': The title protagonists, Jake and Jennifer Eagle. Besides the obvious gender differences, he's a red-head and she's brown-haired.

* Prince Alaric and Princess Alana, in ''VideoGame/CuteKnightKingdom''. [[spoiler:They're so identical that for a long time, they get away with pretending to be a single individual called Al. The observant player, however, will note that their eyes are different colors.]]

* ''VideoGame/AssassinsCreedSyndicate'': Jacob and Evie Frye, who have enough similar features people easily identify them as twins. It's a bit more of an InformedAttribute though, as while Henry describes them as being equal in height and have matching dark hair, Jacob's hair is darker and he's visibly quite a bit taller, and looks older thanks to a crooked nose (as he's more prone to fighting) and unshaven facial hair. There's enough similarities you can tell they were ''probably'' this when they were younger, but the two went through significant DivergentCharacterEvolution as they got older thanks to Jacob's roguish behaviour and Evie's scholarly pursuits.

* Walky and Sal in ''[[Webcomic/WalkyVerse It's Walky!]]'', Less so in ''Joyce and Walky.'' And not at all in ''Webcomic/DumbingOfAge'', due to ArtEvolution, with the fact that they do have differences (in particular, Sal claims ParentalFavoritism for Walky because he "came out more white" while she has naturally kinky hair) is a point of contention between them. Although it might be there on ''some'' level, as Walky has mentioned that he's been mistaken for Sal before.

* Sam and April of ''[[http://www.drunkduck.com/dragon_city/ Dragon City]]'' look identical aside from gender and April's glasses, but according to the FourthWallMailSlot they actually are identical, gender in dragons is influenced by incubation temperature (as in crocodiles) rather than genes. Every other set of twins in the comic are obviously fraternal, even having differently colored scales.

* ''Webcomic/{{Hooky}}'' features the twins Daniella and Dorian Whytte. As twelve-year-olds, they look alike except for their hairstyles and [[CoordinatedClothes - although matching - clothes]], to the point that a major plot point in the first part of the webcomic is the question which of them is featured in an important prophecy.

* WesternAnimation/EdgarAndEllen look exactly the same except for Ellen has long hair in pigtails and no bangs. They even dress exactly alike.
* {{Downplayed}} in ''WesternAnimation/GravityFalls'': Dipper and Mabel, the main characters, are twins with identical bodies and faces with the exception of small skin details (rosy cheeks for Mabel, eyebags and a red nose for Dipper); Mabel also has braces. The resemblance isn't generally brought up, as their clothes and personalities are closer to PolarOppositeTwins. In the defictionalized Literature/GravityFallsJournal3,'' Dipper writes that Mabel looks like him but with "girl hair."

* There's also the less rare instance where fraternal twins of opposite sexes simply have such a StrongFamilyResemblance that they can pass for each other... at least till puberty, anyway. Even then, there are boys who are a bit {{Bishonen}}, and girls who are a bit {{Bifauxnen}}...
* This can also happen if opposite-sex twins are babies with short/no hair. All babies look alike, when they're that young.
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** Palom and Porom from ''VideoGame/FinalFantasyIV'' qualify as this. The original sprites lacked sufficient detail to make it clear whether they were meant to be identical or simply share a number of similar traits and style of dress; but the CG renders in the 3DS edition depict them as having identical facial features.

* ''WesternAnimation/GravityFalls'': Dipper and Mabel, the main characters, are twins with identical bodies and faces with the exception of small skin details (rosy cheeks for Mabel, eyebags and a red nose for Dipper). The resemblance isn't generally brought up, as they dress completely differently, and Mabel also has braces. In the defictionalized [[Literature/GravityFallsJournal3 Journal 3]], where Dipper writes that his sister looks like him but with "girl hair".

* ''Webcomic/TigerTiger'' is about the noblewoman Ludovica takes the identity of her twin brother Remy in order to seek adventure and pursue her dream of studying sea sponges. Sure enough, the siblings look similar enough for her to pull off the charade, though they are actually drawn in subtly different ways, such as in the shape of their jaw. The most obvious difference is how Remy's BeautyMark is by his eye while Ludo's is at the edge of her lip.