S Cry Ed was completely based around this trope, with Kazuma and Ryouhou being eternal red/blue rivals.
Athena and her assistant Nike in Appleseed are complete opposites but work extremely efficiently together running the city of Olympus, with Athena keeping the public and the politicians in check mostly by sheer force of will and Nike serving as her Noble Top Enforcer behind the scenes. In the anime, Athena has red hair and dresses in red and brown, while Nike is pale blond and dresses in white and blue.
Jin and Mugen from Samurai Champloo. They are not only dressed in the respective colors and are foils, they represent every trait possible of the trope. Water and fire (fish and rooster in the OP), past and future, tradition and innovation (Technician Versus Performer), orthodox and unorthodox, predictable and unpredictable, economy and extravagance, controlled purpose and chaotic energy, order and chaos, stoicism and emotion, etc. Jin is practically unable to feel passionate about anything or form attachments to anyone, while Mugen is recklessly passionate without direction or purpose (or the brain power to put it to use). Fortunately, they get better throughout all the whirls of yin and yang.
The Elric brothers: Edward (red) and Alphonse (blue). Ed is typically more impulsive and quick to anger and wears a red coat, while Al is a more collected Gentle Giant who typically has to restrain his older brother and happens to be a cool gray suit of armor.
Made quite blatant in the fourth Brotherhood opening — the two pass each other and gain their respective colors.
Also kind of interesting is that all of the other State Military characters wear blue uniforms, and the Xingese characters also tend toward either blue or more muted colors, and Ed is one of the most Hot-Blooded characters in the cast. On the other hand, he's a unique example of a highly intelligent Red Oni.
From the first anime, there's Winry and Sheska. Winry is extraverted, enthusiastic, and sometimes wears a red bandanna, while Sheska is quiet, bookish, and sometimes wears a blue uniform.
Also from the first anime, Ax-CrazyBlood Knight Kimblee, whose main outfit before being re-instated is a red buttoned shirt, and cold-blooded General Ripper Archer, who's never seen in anything but his blue military uniform, would be villainous examples.
Ayano and Kazuma from Kaze no Stigma. Ayano has a fiery, impulsive, very caring personality, while Kazuma has a calm, impassioned, jaded personality. The colors fit them too; in the OP, Ayano is colored red and Kazuma blue. Kazuma has blue eyes when his power is activated and a general blue theme, and Ayano has red hair and reddish eyes.
The manga has Usagi/Minako as impulsive, outgoing red, with Ami/Rei as cool, introverted blue. Makoto's in the middle. As for the first anime, Rei contrasts better with Ami, since Rei is just as impulsive as Usagi and is actually a fire soldier to counteract calm Ami's water powers.
While Haruka and Michiru both had the same intentions in season 3, Haruka's attitude was more outgoing and harsh in comparison to Michiru's calmer, more introvert demeanor.
Also, Inuyasha and Miroku, each dressed in their respective color.
An arguable case is Ogami Itto and Yagyu Retsudo from Lone Wolf and Cub. Although Itto doesn't have the not-so-bright or tasteless qualities of many red oni, he is driven to incredibly reckless behavior and horrid deeds by a passion for revenge, while Retsudo prefers being the puppetmaster and using traps, mooks, and the like. Along the way, he sacrifices an appalling amount of men and his own children in his attempts to stop Itto.
Light and L from the Death Note anime series are often shaded in red or blue to reflect this, although personality-wise, it doesn't quite apply, since aside from a few times that Light gets riled up after his cause is challenged (and just before his death)both Light and L tend towards being brainy, cold blooded types. However, Light tends towards extremes of fantasy and pitches of emotion that L never begins to approach. This theme is also used (and generally played much straighter) with Misa and Light, Light and Near, Mello and Near, and even Misa and Takada.
In the 1980 sci-fi manga and 1988 anime film adaption "AKIRA", the two main character is based on this trope; Hot-head Kaneda tend to be Red Oni compared with (a little) Blue Oni Tetsuo
Goku and Vegeta of Dragon Ball Z exemplify this trope to a point where it could be named for them (And for a while, it was).
Although it's hard to remember now, but when Vegeta was first introduced, he seemed like a cold-blooded and heartless killer, one who seldom emoted more than wearing a Psychotic Smirk when killing someone. It wasn't until Goku proved himself an equal, if not superior in fighting ability (something that goes directly against Vegeta's pride, the Saiyan traditions, and culture he prizes so, etc), that Vegeta starts going off the deep end. Even then, it's worth noting that, in the description, it does say that (especially for villains) the calm, unemotional face of a Blue can just be a facade and conceal a lot of intensity and even craziness right below it. (Oh, and Piccolo is definitely a Blue type as well.)
When introduced, Vegeta played the Blue Oni to Blood Knight Nappa's Red.
Another example from Dragon Ball Z: Goku encounters a literal red and blue oni in the first season. It's inverted, as The Big Guy bruiser is a blue oni (who gets beaten quickly in a contest of strength), while the faster and more clever red oni challenges Goku to catch him and spends half the episode dodging the hero.
This can be traced to the very first episodes of the series with strong but dumb Goku and sly and crafty Bulma.
Goku's children fits this too, with Gohan being the blue and Goten being the red.
On the same side, but Ryoma and Hayato from Getter Robo definitely fit. Ryoma's a heroic burning-sense-of-justice type (well,mostof the time...), while Hayato is a cold-blooded loner. This is taken into extremes in Getter Robo G, where Ryoma's Getter Dragon is red and Hayato's Getter Liger is blue!
In Black Butler Alois is the Red Oni to Ciel's Blue Oni. Alois is impulsive and more outgoing than Ciel while Ciel is clam and collected. They both have a red and blue color scheme respectfully as well. It's further driven home after Alois' soul is trapped in a ring by Claude, it's red in contrast with Ciel's ring.
Naruto and Sasuke (complete with the colors of their clothing and demon forms). In the third opening of Naruto Shippuden, "Blue Bird", the pair are shown against a red-and-blue background◊. Unusually, Naruto has wind-based powers, while Sasuke's are fire-based.
Other Red Oni/Blue Oni pairs include Lee and Neji, Jiraiya and Orochimaru, Guy and Kakashi (and, before that, Obito and Kakashi), Kiba and Shino, Choji and Shikamaru, and arguably even Kankuro and Gaara (at least after his Heel-Face Turn). With Choji and Shikamaru, Choji is easily set off and uses close attacks while Shikamaru is known to think things through thoroughly and always be ten steps ahead, and he also uses his shadows to attack from a distance. Shikamaru is not exactly blue but he does have a cool-color based theme while Choji has his bright red symbol, and in Shippuden, his outfit is nearly all red.
To a lesser extent, their dads qualify. Shikaku is a fiercely intelligent, rational strategist and Jounin Commander of Konoha. Choza is calmer than his son, but is still the fieriest of the Ino-Shika-Cho trio, and he has red hair.
The color scene is inverted with Akatsuki partners Itachi and Kisame, the former being a cold, calculating Aloof Big Brother with red eyes and several fire jutsus, the latter being a Blood Knight that specialises in Water Jutsus and has the blue skin of a shark.
See also Juugo and Suigetsu. Juugo has red hair, but is a Gentle Giant when he's not flipping out and is the calmest out of Taka. Suigetsu, meanwhile, is a white-haired Blood Knight from the same village as Kisame.
A few of the Akatsuki pairings invert this. Between Sasori and Deidara, Sasori has the orange eyes and Deidara has blue.
Despite their hair colors mismatching the trope(at first), during near the end of Pein's fight with Naruto. Pein became the Red Oni by losing his emotionless attitude and slowly turned drastically infuriated when fighting the enraged Jinchuuriki. Pein's Blue Oni exterior finally faded showing what many years of torture can do to you. Konan proved to be the Blue Oni after warning Nagato not to over-exhaust his power, and attacks her foes when it is truly personal or ordered to. This is a clever example of how both Oni's can switch at any time of a story.
Lately, Sasuke has been showing a few Red Oni traits, while Naruto has been showing some Blue Oni traits. But I wouldn't switch the names quite yet.
However, before and after the Uchiha Massacre Sasuke was the red compared to Itachi's blue.
Then there's Hidan and Kakuzu. No colour association, but jeez, the contrast couldn't get much stronger.
Lets not forget the two Senju brothers Hashirama and Tobirama, their armours colour makes it obvious and the fact that Hashirama has more involvement in the Leaf's past than his brother despite both of them were Hokage.
The Two Snake Shinobi Orochimaru and (eventually) Kabuto can fit. Orochimaru was the Red Oni as he sacrificed too much and recklessly in his quest for power which ultimately resulted in his death. Kabuto was the Blue Oni who patiently followed the latter and even became a far greater threat, manipulating more appropriately.
Bleach: There are a lot of examples but many of them can be much more complicated or even the reverse of what they might appear to be. Kubo loves playing with this trope.
Played straight with Ichigo (Red) and Ishida (Blue), Ichigo (Red) and Byakuya (Blue), Renji (Red) and Byakuya (Blue), Renji (Red) and Ishida (Blue), Kenpachi (Red) and Byakuya (Blue), Ginjou (Red) and Tsukishima (Blue), Hitsugaya (Red) and Gin (Blue), Hiyori (Red) and Shinji (Blue).
Played with in the case of Orihime and Rukia where Cloud Cuckoo Lander, orange-haired Orihime should be the red and Ice Person Rukia should be the blue. However, the wild, passionate, forceful character is Rukia and the quiet, introverted character who would rather fade into the background is Orihime. This is especially highlighted when Urahara pulls Orihime off the frontlines. Orihime accepts the situation sadly but without protest while Rukia goes on the warpath to get Orihime back to the frontlines...even if she has to drag Orihime there herself to do it.
Mayuri Kurotsuchi is a captain that many characters fear mostly because of his appearance and disturbing attitude towards human experimentation that borderlines psychopath, However Nemu is calmer, more approachable but just as dangerous nonetheless.
Played with in the case of Aizen and Ichigo. Aizen is the blue to Ichigo's red until their Deicide battle when Ichigo becomes the blue to Aizen's red.
Subverted with Tsukishima versus Byakuya. Being two characters who traditionally take the Blue role, this trope shouldn't have come into play at all. Except it did. With Byakuya as the red oni. Discussed by the pair during the fight.
Subverted with Aizen and Gin. Throughout the manga, it looks like Aizen's the blue oni to Gin's red. It turns out to be the reverse.
Rurouni Kenshin has Sanosuke and Kenshin, who are even cast in their respective colored lights during their first battle. After losing, Sano becomes The Lancer.
A lot of the time, Kenshin becomes the Red Oni, especially compared to stoic antagonists such as Saito and Aoshi
In Fruits Basket, temperamental, red-haired, red-eyed Kyou and calm, blue-eyed, grey-haired Yuki are cousins and rivals in love, martial arts, and, to some degree, even social life, each one envying the other's abilities in dealing with people.
Tohru's friends, Arisa and Hanajima, have this going on. As did Tohru's parents: Kyoko was brash and excitable while Katsuya was calm and polite to a fault.
In Majokko Meg-chan, Meg and Non are the Red and Blue respectively, complete with conveniently color-coded hair.
Zenon and Shien, the two gods that appear about halfway through Gensou Maden Saiyuki.
The titular duo of Futari wa Pretty Cure: Nagisa is the lacrosse-playing tomboy who wears the black and red costume, Honoka is the intellectual one in the white and blue dress. At one point, they even fight a pair of red and blue Oni just to drive the trope home.
In Yes! Pretty Cure 5, this trope is played both straight and inverted. Cure Rouge and Cure Aqua play it straight, complete with a story showing how their opposite personalities clash. However, while Nuts usually wears red and Coco wears blue, especially in their human prince forms, Nuts is the quieter, more aloof one of the two, so they are the inversion of this trope (with the quieter one wearing red).
In Fresh Pretty Cure!, Love is the red oni to Setsuna's blue. Interestingly, Setsuna is the who wears red while Love wears pink, but Setsuna also wears darker colors (especially black) in contrast to Love's bright clothes.
HeartCatch Pretty Cure! also inverts this. The pink-wearing Tsubomi is a shy and introverted blue oni; her partner, the blue-wearing (and water elemental!) Erika, is an outgoing and energetic red oni.
It's played straight again with Smile Pretty Cure! and its rainbow theme with Miyuki and Akane as Red and Nao and Reika as Blue. Yayoi (Yellow) falls in between.
In Doki Doki Pretty Cure, Mana is the red oni to Rikka's blue oni. Also, Alice and Makoto are blue onis to Mana's red. However, when Regina is there, she becomes the red oni to Mana's blue oni.
Kiddy GiRL-AND has the antagonist duo Saphir and Rubis, with Hair Colors to match their names (though Saphir's hair is actually closer to green than blue), with the "blue" one able to use ice-based attacks (the "red" one doesn't use fire, though, but rather is a beast-humanoid with long claws), and with contrasting personalities in line with this trope.
Zatch and Brago from Zatch Bell!. Also, Zatch and his Evil Twin Zeno, later on in the series. The former is a kind, but childish boy who wishes to be friends with anyone he meets, while the latter is a cold, manipulative person who hates humanity and bears a grudge towards Zatch, though this is only because Zatch received the Baou power instead of him. Their owners and even the color of their books reflect this as well.
Asuka Langley Soryuu and Rei Ayanami from Neon Genesis Evangelion also satisfy this trope, although more in the rivalry sense, as Asuka despises Rei and Rei is characteristically indifferent to Asuka much of the time. That doesn't stop Studio Gainax from pairing them up in merchandising, though.
Note that their 'theme colour' is inverted in their eye colour: Rei is blue-haired with red eyes, Asuka is a redhead (or a blonde in the manga) with blue eyes. This arguably reinforces their contrast and even complimentarity.
Their mecha are, however, all red and all blue respectively and explicitly compared to oni in concept and design just to be obvious.
If you look at the colors of the mecha and plug suits, Shinji appears to be the blend of the two: not a hot-blooded glory hound but not a heartless machine, completing the Power Trio.
Misato (red) and Ritsuko (blue).
In Gundam Wing there are two mobile suits designed to complement each other in battle: Vayeate, a blue colored suit that specializes in attack, and Mercurius, a red colored suit that specializes in defense.
∀ Gundam features Sochie Heim, a feisty (read: bratty) tsundere, and Miashei Kune, her relaxed and practical friend, who both wind up piloting Kapools and partner with each other often.
YuYu Hakusho has literal blue and red oni — the blue oni are the bureaucrats in the Spirit World, while the red oni are security. With the protagonists, Yusuke and Kuwabara are both brash and eager, ready to throw themselves at a challenge, while demonic protagonists Hiei and Kurama are far more calculating and keep much cooler heads about them.
Every season of Digimon has at least one hero and teammate that make up this duo.
Digimon season 2 has the high-energy, somewhat brash gogglehead Daisuke paired with introverted intellectual villain Ken, who pulls a Heel-Face Turn halfway through the series. While enemies, they repeatedly face off; while allies, they find out that their digimon can combine into a much stronger digimon, linking their characters even more than before. Furthermore, Daisuke felt a kinship with Ken before they learned that he was a villain and, of all the other heroes, was the most sympathetic toward Ken during the time between repentance and alliance. Oh, and on the Blue Oni quality of "pride and aloofness": after his repentance, Ken spent a long time apart from the hero group, trying to "clean up his mess" in his own way, and worried that even if he tried to join up, they wouldn't accept him.
In the first half of the season, T.K. was the Blue Oni — smarter, more level-headed and rational than Davis. With Ken's arrival, T.K. sort of became the third banana, though.
Just 02? Let's see, in the first Adventure, we have the main character, Taichi, who Daisuke is an Expy of, and so they share a lot of personality traits (albeit Taichi's are toned down a little), and Aloof Big BrotherLancer Yamato, who spends most of his time trying to figure out what will keep his younger brother safest. While Taichi is unrestrained emotionally, Yamato is more prideful and tends to get embarrassed quickly at activities that lower him down to Taichi's level. Taichi is associated with the color orange (at least it's close to red) and Yamato with the color blue.
Just Digimon Adventure? Masaru and Touma in Digimon Savers. There are specific episodes built around their might vs. mind clashes, and Touma seems particularly afraid of losing his coolness and intelligence in the face of Masaru's determination and charisma. Nanami taunts him with the fact that he didn't defeat with his prided logic and calculations; he beat her by charging at her head on, Masaru-style, and this seems to disturb him. Their DATS uniforms (red bodysuit with blue jacket for Masaru, blue bodysuit with blue jacket for Touma) reinforce this...heck, there's an absolutely hilarious Image Song dedicated to them (and Agumon and Gaomon) explaining why their personalities and methods clash, but they're still the greatest team...right?
In short, all seasons of Digimon invoke this trope.
Interestingly, in all of the seasons of Digimon save Digimon Tamers, the Blue Oni/Onis have blue eyes while the Red Oni has brown. In Digimon Tamers, this is reversed (at least, if you count Ruki's indigo eyes as blue).
Duck (or Ahiru in the Japanese version) and Fakir from Princess Tutu follow this trope very well. Duck has orangy-pink hair and is a loud, determined, dizty klutz who cares deeply about people and wants to be everyone's friend. Fakir is a green-haired boy who is cold, seemingly prideful, and anti-social. They start off as bitter rivals but later discover they have the same goal — to help and protect Mytho — and end up becoming awkward partners. In the second season, Fakir develops a crush on Duck and the two become even more closely associated.
Keroberos and Yue of Card Captor Sakura fame also qualify; Blue Oni Yue is often cold, introspective, and seemingly totally dispassionate, while Red Oni Kero-chan is hot-headed and emotional.
In the anime, Sakura switches to Blue Oni when she's around the more Hot-Blooded Li Meiling.
Sakura Kinomoto (red) and Li Syaoran (blue). A bit of a twist happens when the Red and Blue Onis actually fall in love.
Jonouchi (Joey) and Seto Kaiba from Yu-Gi-Oh! follow this trope to the letter, right down to their trademark cards.
Sometimes, Honda (Tristan) is the blue oni to Jounochi's red oni when Kaiba's too busy, Honda being more romantic, quiet, contemplative, and likely to choose his battles than Jounochi.
Yu-Gi-Oh! 5Ds has Yusei Fudo as the Blue Oni and Jack Atlas has turned to be the Red Oni. Remarked with Yusei's blue Stardust Dragon and his Clear Mind and Jack's Red Dragon Archfiend and his Burning Soul.
On the villains' side, there's Heartland's two henchmen, the high-spirited and energetic Gauche, and his partner, the cold and stoic Droite. (To emphasize this, their names are French for "left" and "right", respectively.)
In Trigun (especially on the manga covers), Vash is associated with fiery reds and poses full of dynamism while Wolfwood is associated with blue and grey tones and more static positions. Bonus points if Wolfwood also glares coldly at the reader. This is an accurate representation of the contrasts between their personalities.
Vash vs. Knives is a more complex case: Knives is the brainy and coldly rational part of the "duo", but he's also incredibly violent and psychologically unstable. While Vash is a passionate and dynamic character, Knives is prone to feeling lonely and depressed and tends to hang around doing nothing. Moreover, Knives's grand theories actually hide his crazy irrationality, while Vash is able to think with a cold head so as not to take personally all the shit he takes from humans. Manga Knives is often associated with blue and aqua colors, but also with darker reds than his brother. Also, note that, during their fight at the end of the anime, Vash's vortex is blue and Knives' is red.
GaoGaiGar: EnRyu and HyoRyu, red and blue. Later, they get taken over by yellow RaiRyu and green FuuRyu, respectively. And then again by light pink KouRyu and dark purple AnRyu. They even represent elements - EnRyu's fire, RaiRyu's lightning, and KouRyu's light for the Red Oni side, and HyoRyu's ice, FuuRyu's wind, and AnRyu's darkness for the Blue Oni side. And it's interesting to note that when the first two pairs switch Fusion Dance partners, they switch across Red Oni, Blue Oni boundaries: EnRyu combining with FuuRyu, HyoRyu with RaiRyu.
GaoGaiGar himself and King J-Der. Twist: GaoGaiGar's G-Stone is green, while J's J-Jewel is red. Also, GaoGaiGar is a mostly black-colored robot while King J-Der is mostly white.
Chrono Crusade reverses the color-coding: Rosette is Hot-Blooded, brash, energetic, and reckless, but wears a blue nun uniform. Chrono, who serves as her lancer, is calm, sensitive, and the voice of reason, but wears a striking red coat. However, Chrono himself does have a dangerous temper which flares up at times.
In the movie Tokyo Godfathers, homeless Transvestite Hana uses the story of the red and blue oni to illustrate a point to tomboyish runaway Miyuki; in it, Hana explicitly compares himself herself to the blue oni and the gruff but good-hearted Gin to the red oni.
Miriya/Max from Super Dimension Fortress Macross. Or the updated version, Klan/Michael from Macross Frontier. In both, they pilot appropriately color-coded mecha. Although, rather than being rivals, they end up love interests, but hey, what's the difference?
In a weird way Sheryl and Alto qualify for this trope as well, as their aura color is Red and Blue respectively due to Chromatic Arrangement, but the attitude between them and their individual behavior when it's just the two of them (most notably in episode 5) fits. Possibly unintended, as the Chromatic Arrangement doesn't appear in its finalized form until much later in the series.
Guts and Griffith from Berserk, with Guts being the violent, determined, and impulsive Red Oni to Griffith's cool, calculating, and exceedingly ruthless Blue Oni, the ruthlessness even more pronounced when Griffith goes bad. And Guts, in keeping with the Red Oni, swears unholy vengeance upon Griffith after the horrible betrayal that wiped out the rest of his True Companions and ended the anime.
Lampshaded in Berserk Abridged, with Zodd comparing the two with Naruto and Sasuke, though Griffith notes that Guts is way more Emo than he is. And as noted, Griffith does indeed turn into a "winged lipstick monster" by the name of Femto upon his Face-Heel Turn.
Pokémon: Ash, the Idiot Hero, as the perfect example of the Red Oni, while Gary, The Rival, definitely qualifies as the Blue Oni. Paul, Ash's new rival, seems to have taken over the Blue Oni role, mixed with Jerkass. To a lesser degree, Zoey and Nando also qualify.
From the first movie: the cute and cheerful Mew as the Red Oni to the Badass and angsty Mewtwo as the Blue Oni.
Pokémon Special features the heroic trainer Red and his rival, Oak's nephew, Blue. In the Japanese original, Pokémon Special, however, this was not the case, as Red's rival was Green, while Blue was the female trainer that the English-language version called Green.
Gold and Silver fit the trope better, although they don't get the colors.
Inverted with cultured, urbane Ruby and wild, tomboyish Sapphire.
Diamond (quiet, thoughtful and lazy) and Pearl (loud, rash and hyperactive) use this as part of their double act and their team make ups (Diamond's are all mighty glaciers while Pearl tends towards fragile speedsters)
Kamina and Simon — blue-shirted and blue-eyed Simon is the comparatively rational one of the two, while red-caped and red-eyed Kamina is...well, Kamina. Kamina is also the Red to Yoko's blue.
Later, Simon becomes the red to Rossiu's blue.
On the villain side, the four Beastman generals have this dynamic as well, in a way. Thymilph and Adiane, the fire and water generals, are off-the-wall BerserkerBlood Knights, whereas Guame and Cytomander, the earth and air generals, are much smarter, calmer, and more calculating.
In Gundam SEED Astray, Lowe Guele (loud, dramatic, impulsive) pilots the Astray Red Frame and Gai Murakumo (cool, intelligent, professional) pilots the Blue Frame.
In Prince of Tennis, Kaoru Kaidoh (skittish, kinda naĂŻve, aloof) and Takeshi Momoshiro (cheerful, a bottomless pit, carefree) might not dress in red and blue, but otherwise, they fit the trope to a T. And yes, they play doubles.
In Hyoutei, we have the flighty and loud redhead Gakuto Mukahi and his doubles partner, the suave Yuushi Oshitari (who has blue hair).
One Piece has two giants, Dory and Brogy, respectively titled "The Red Ogre" and "The Blue Ogre" on their wanted posters, although they both act the same to this troper
Nami and Nico Robin also fit this dichotomy as the two women aboard. Orange-haired Nami tends to react loudly and angrily to the crew's stupid antics and gets very passionate over money, while black-haired and blue-eyed Robin is introverted to a fault, reacting quietly to everything short of a world-ending crisis.
Not to mention Nami and Vivi, whose hair (orange for Nami, sky blue for Vivi) even helps to fit this trope. Nami, as mentioned above, is short-fused and quick to react with anger, while Vivi is sweet and sensible. In a crisis, however, this trope is completely inverted; Nami usually is the one to react with a plan, while Vivi has a meltdown.
For the Marines, Admiral Akainu (Red), who is prone to passionate bouts of well-intentioned extremism, and Admiral Aokiji (Blue), who is very laid back. Even their names reflect this—"aka" is red, "ao" is blue. Also, they are bitter rivals.
A friendship-based duet of the kind in the Marines are Sengoku and Garp, with Sengoku usually being the cool one and Garp the emotional one.
The second season changes things up by introducing Vita, a tiny girl clad in red that carries around a massive hammer with a hair-trigger temper. Throughout the second and third seasons, she is the Red Oni and Nanoha, who by this time has become much more level headed and calculating, is the Blue Oni among the Wolkenritter.
Highlander: The Search for Vengeance features a strong Red vs Blue rivalry between its protagonist and antagonist. Colin is a red with a two thousand year old grudge against the Roman general who slaughtered his people and wife; the blue Marcus cares only for bringing "civilization" and order to the world.
If you look closely, the Haruhi Suzumiya series contains a very subtle subversion. At first glance, it may seem as though Yuki (quiet, rational, and unemotional) is the Blue Oni to Ryoko's (cheerful, pleasant, compassionate, and somewhat Ax-Crazy) Red, but actually, it's reversed. Over the course of the series, it's revealed that beneath Yuki's expressionless face exists a complex inner world which comes boiling to the surface in the fourth book/second season, while Ryoko is actually a ruthless and emotionally vacant Stepford Smiler whose foiled attempt on Kyon's life was actually a calculated act designed to prompt a reaction from Haruhi.
In the 6th episode of the Endless Eight, Kyon wore red swimming and Itsuki wore blue.
Also, in the 13th (11th) episode of Season 1, Haruhi is wearing a red uniform, while Kyon is wearing blue.
The two ghosts (or whatever they are) in The Tower of Druaga, although it's not immediately obvious for two reasons: one, the red girl doesn't show up until episode 8, and it's not the girls themselves that demonstrate the appropriate personality, but rather the person to whom they appear. The blue girl shows herself to Neeba, while the red one appears to Jil.
Noa Izumi and Kanuka Clancy from Patlabor. One is a slobbish redhead without a college degree who constantly rushes into trouble; the other is a super-professional MIT graduate with glossy black hair (that looks blue) who never lets any situation get to her.
Dragon Quest: Dai's Great Adventure has the clashes between super-Hot-BloodedMaam and borderline cowardly Pop. They're respectively dressed in red and pink and in green. Maam and The Stoic Hyunkel form an even bigger contrast, but they get along well while a large amount of screentime is devoted to the conflict between Pop and his "badass goddess of luck". Also, notice that Maam is a martial arts specialist and Pop a mage. Avan and Hadler are another interesting case, with Avan as the silly, warm-hearted, and spontaneous red oni (he's gotta have blue hair, but he's dressed in red]]) and Hadler as the stubborn and fiery but cold-hearted and stoic green-skinned warrior. Pop and Hadler become increasingly like their counterparts - the former through The Power of Friendship and the latter through the magic of Foe Yay.
D.N.Angel has Daisuke Niwa as red and Satoshi Hiwatari as blue, very obvious in their theme colours. Dark and Krad are rather associated with black and white, though they may also be seen as the grown-up and cynical equivalents of their hosts.
Code Geass has scenes where Lelouch and Suzaku are shaded in red and blue respectively, though it counts as a subversion: Lelouch is the cold, tactical one and Suzaku is brash and reckless...but in the end, both can be hotblooded and irrational under pressure.
Lelouch's first Evil Counterpart (and Worthy Opponent) Mao is also a red Oni to Lelouch's blue in a way: Mao is emotional, impulsive, completely concerned with the people around him C.C., and has no concern for the political climate or anything bigger. Lelouch is (relatively speaking) cool, intellectual, sophisticated, and has lofty political ideals. It makes for an ironic form of Color-Coded for Your Convenience in that Lelouch wears a reddish-brown jacket and Mao wears a blue-and-white great coat.
And Lelouch and C.C. are red and blue Oni respectively as well, perhaps even better. Lelouch is, after all, very passionate and C.C. is a detached, sarcastic Stoic.
In maps, Brittania is blue and the UFN is red.
In the final arcs of the series, Lelouch is red and Schneizel is blue, even though they are both ruthless and calculating Magnificent Bastards.
The final opening theme parodies this color-coding, having Schneizel and Charles under Red/Blue light, meaning they have a cold and an impulsive sideďż˝then Lelouch appears, and his light is a full rainbow. Don't try to color-code Lelouch, folk: he's more complicated than that.
Sakuragi and Rukawa from Slam Dunk. Heck, Sakuragi even has red hair; not to mention, Rukawa has blue eyes (anime only).
In Mai-HiME, Mai Tokiha is the Red Oni (emotional, passionate, concerned with people) and Natsuki Kuga is the Blue Oni (aloof, mysterious, and concerned with goals). They even have hair colors to match (Mai's is reddish-orange and Natsuki's is bluish-violet).
Mirrored by Arika (red) and Nina (blue) in Mai-Otome. In the prequel mini-series, Nina's mother Sifr plays Red to Arika's mother Lena's Blue, seemingly just for the irony.
Interestingly, at various times during the anime series, each member is represented by a coloured rose. Kyouya's is a pale blue, almost mauve, whereas Tamaki's is white. The red rose went to Haruhi.
Alternatively, the twins Hikaru and Kaoru represent the red and blue oni, respectively. It's not always obvious, since they tend to use the 'Identical twins' act, but a few episodes that focus on the twins delve into this aspect. Exemplified in one episode when, each twin trying to distinguish himself from the other, Hikaru dyes his hair pink (red) and Kaoru dyes his hair blue.
One color may be off, but Keroro (green) and Giroro (red) not only exemplify this trope, they even drag out the trope namer and elaborate on it in one episode.
Shaman King loves this. Firstly, there are several instances where the show uses an overlay of two characters, one in red and one in blue - Yoh, the calm, cheerful protagonist, is always the blue character. Also, Amidamaru, Yoh's spirit partner, condenses into a blue spirit flame in battle, which means that Yoh's various oversouls are all blue as well. The major baddies he winds up fighting (Ren at first, then later Hao) have spirits who manifest themselves in red. Finally, there are Zenki and Kouki, two genuine oni who are actually red and blue.
In Fushigi Yuugi, friends-turned-enemies Miaka and Yui. Miaka, who is impulsive and passionate, becomes priestess for the god Suzaku, whose element is fire. The more coolheaded Yui becomes priestess for the god Seiryuu, whose element is water.
A friendly version is done among the male characters: Vitriolic Best Buds Tasuki and Tamahome, and later Tasuki and Chichiri.
The amusing part is that this is a pun on the symbol on Tamahome's forehead. Go ahead and guess what it is.
In Soul Eater, almost every meister/weapon pairing does this.
Maka is a cool, intelligent planner, while Soul is impulsive, emotional, and aggressive. It may say something that the Blue Oni is in charge in this case!
Later on, the roles switch; Maka becomes more headstrong and direct, while Soul becomes more of a calm and cool foil.
Maka's father Spirit/Death Scythe mirrors Soul's traits, with a double shot of lechery. His former meister, Dr. Stein, is much like Maka...except that his curiosity is so strong, it drives him to do medical experiments on people while they're asleep!
Jin and Jo from Innocent Venus. Jin is the smooth talker and nice guy at first; Jo is the intimidating stoic. Appropriately, Jin has white hair and pilots a white mecha and Jo has dark hair and pilots a black mecha. Subverted in that Jin really was the villain all along and Jo is the true hero of the series.
In Axis Powers Hetalia, Red Oni US is cheerful, idealistic, and brash, if a little too much; whereas Blue Oni England is his cynical, grouchy, critical, sometimes underhanded longtime 'frenemy'.
No one's mentioned Denmark/Sweden? Denmark, ie happiest country in the world, is constantly smiling and dresses in red (even his flag is red), whereas the calmer, quieter, and less emotional Sweden is in blue, like his flag.
One could also replace Sweden with Norway, who is constantly stoic and calm, and although his flag only has a little blue, he himself dresses head to toe in it.
Turkey and Greece.
Azumanga Daioh's Red Oni homeroom and English teacher Yukari, who is goofy, carefree, fun-loving, and irrational, and wears bright red and yellow clothes contrasts Blue Oni P.E. teacher Nyamo, who is cautious, caring, responsible, thoughtful, and wears darker blue clothes. Red Oni Tomo and Blue Oni Yomi also fit the trope.
Fai and Kurogane from Tsubasa Reservoir Chronicle, especially through the first arc. They're almost completely colour coded (eyes/clothes even skin colour and hair to an extent) until their positions start to change and Fai starts to crack.
And also, hot-blooded lightning wizard Laxus versus calm, noble, blue-haired staff wizard Mystogan.
One scene in the first Fist of the North Star has Ken and Shin standing next to their master's headstone. As they recall his words about the Nanto and Hokuto being two sides of the same philosophy, Ken and Shin are replaced by a Blue and a Red Oni respectively.
In episode 47, as Ken prepares to fight his brother Raoh, Raoh releases a red aura and Ken releases a blue aura, with both auras filling about half the screen and merging into a purplish haze in the middle.
The main characters of Hunter × Hunter seem to pair off in these. Leorio is the Red Oni to Kurapica's Blue Oni. Same goes with Gon and Killua, Gon obviously being the Red Oni and Killua being the Blue Oni. Heck, they've even stated it themselves; Gon is the one who's supposed to do the stupid stuff and Killua's there to bail him out of it. And Gon absolutely forbids it to be the other way around.
Slayers (movie/OVA timeline) has the rather shy Lina with her quiet, unassuming temper of a bounding mine and narcissistic Naga showing off herself but not keeping a teaspoon of powder in reserve — she isn't wound up at all even when fighting. Lina is leaning toward fire magic and Naga is more inclined to water, though they have personal reasons for this.
The TV Slayers timeline has Lina as a textbook Red Oni with her red hair, red outfit, red eyes, love of fire magic, and red-hot temper. "Heartless magic-using swordsman" Zelgadis is the Blue Oni. Unusually, Lina and Zelgadis are near-equals in intelligence and strategic ability.
Katekyo Hitman Reborn!, with Gokudera and Yamamoto as Red Oni and Blue Oni respectively. In so many ways. A strange balance between rivalsandcomrades, Gokudera has the firey disposition while Yamamoto is almost always composed. Heck, even their Flames correspond perfectly to this trope.
The opening credits of Saint Beast: Kouin Jojishi Tenshi Tan present Judas (blue) and Goh (red) like this, except this assignment only invites Epileptic Trees. When the other way around (Goh->blue, Judas->red) invoking this trope makes quite a bit more sense, especially as both are different interpretations of The Hero.
Shamanic Princess: Tiara (red) and Lena (blue). Or, alternately, Tiara (red) and Sara (blue).
Louie and Genie in Rune Soldier are both very tall and extremely strong, and very good in combat as well. They are also the two characters who are arguing and getting into fights with each other the most. Interestingly, they are the only two characters with unnaturally colored hair, but it's stoic and responsible Genie who has bright red hair and funny guy and troublemaker Louie who has blue hair. While Genie has her violent moments, it is almost always because of Louie's antics.
Played With in Legend of the Galactic Heroes with Wolfgang Mittermeyer and Oskar Von Reuental. Much of the trope is played straight: Mittermeyer is a blond commoner, more brawny and passionate and, in his youth, was clearly a bit more goofy. In any other anime, he could be the Idiot Hero. Reuental is colder and more distant, dark haired and elegant son of a noble family. They are even colour-coded: their otherwise identical flagships have a red stripe for Mittermeyer and a blue one for Reuental, and after the uniform change in Season 3, they sport adequately coloured capes! The playing with comes into play in many ways, firstly because they are best friends rather than rivals. Secondly, because they are both masterful tacticians and very brawny. However, their tactical preferences for commanding fleets are quite different: Mittermeyer prefers swift attacks, while Reuental prefers a slower, more calculating approach, thereby matching the trope.
Hayato Kazami and Bleed/Jotaro Kaga in Future GPX Cyber Formula seems to be this at first, but eventually subverts this, as they are a mix of both red and blue oni traits. In addition, Kaga's car is reddish-purple (in the TV series) and Hayato's is blue (but it's a white car with blue trimmings).
Kyoko Sakura and Sayaka Miki in Puella Magi Madoka Magica, right down to the respective colors of their hair, eyes, and combat outfits. Madoka (outgoing, cheerful) and Homura (distant, aloof, collected) also fit, including their color identifiers (pink, gray).
Madoka and Sayaka, meanwhile, the two best friends at the start of the series, count as an inversion of sorts - Madoka is pink and Sayaka blue, as already mentioned, but gentle, slightly ditzy Madoka is definitely the blue oni to boisterous, Jumped at the Call Sayaka's red oni in terms of personality.
Finally, though it's not reflected in the colour-coding, both Madoka and Sayaka could be seen at the beginning of the series as the naďve red onis to Mami's calm, experienced blue. It seems that Kyouko might also fulfil the red oni role to Mami in the prequel manga much as she does to Sayaka in the anime.
And pretty much everyone ends up playing the red oni when interacting with Kyubey.
Guy Double Target stared Reina, the cheerful, whiney, and outgoing red oni, and Guy, the collected, sensible, and serious blue oni.
From Seven of Seven, Nanappe is hot-tempered, violent, wields a red crystal, and wears a red Nana Ranger costume. Regular Nana is much more calm, rational, and level-headed, wields a blue crystal, and wears a blue Nana Ranger costume.
In Rosario + Vampire, the two main characters are Aono Tsukune (the only human among monsters and often the Only Sane Man) and Akashiya Moka (who's much more excitable, to say nothing of her true vampire personality). Most of the other characters also have colour-based names.
Go Lion plays with this trope. Isamu has all the stereotypical characteristics of the Red Oni: impulsive, rebellious, loud, confrontational, outgoing, nervous...but wears a blue uniform, while still piloting the red lion! Akira has the Blue Oni traits: levelheaded, cool-minded, rational, quiet, calm, composed, judicious, reasonable...but wears the red uniform and civilian attire! Fala has an even mix of traits from both red oni and blue oni, wears a pink uniform and civilian clothes, and pilots the blue lion.
The eponymous duo of Tiger & Bunny exemplify this. Heroes with identical abilities forced to work as partners by their sponsoring company, their personalities and views on their profession are vastly different. Wild Tiger is the Red Oni - relying on emotion, instincts, and personal beliefs in justice to guide him; Barnaby is the Blue Oni - relying on logic, reason, and the best interests of his sponsors instead.
Their color schemes are actually inverted. Tiger originally wore blue but moved on to green (still a "cool" color) early on in the series; in constrast, Barnaby wears red, a "warm" color.
Color coded in Panty & Stocking with Garterbelt: Panty has red nails and usually wears shades of red and Stocking wears shades of blue. Even their weapons are color coded: Panty's gun, Backlace, is a pair of pink panties before transformation and Stocking's katanas, Stripe I & II, are a pair of blue and black striped stockings before transformation.
Character-wise the Angel sisters are the red onis, compared to their rivals the Demons sisters Scanty and Kneesocks who are the blue oni (despite their red skin). Though Panty and Scanty serve as the Red sister, while Stocking and Kneesocks serve as the blue sister from both groups.
Durarara!!: Shizuo Heiwajima and Izaya Orihara. Masaomi Kida and Mikado Ryugamine.
Also, Walker and Erika collectively play red oni to Kadota's blue.
Shizuo Heiwajima gets two, actually — when Izaya isn't around, his Benevolent Boss and middle school sempai, Tom Tanaka, acts as his blue, complete with meeting the insanity caused on a daily basis with tolerance and facepalms. He's not without his moments, though.
Tom: You guys never heard of Heiwajima Shizuo? You guys really did go to public school...
In Lotte no Omocha, Lotte and Asuha even wear the matching colors for their roles (Asuha wears pink, but close enough).
In Night Raid 1931, Aoi is a red oni, being friendly and easygoing, is very open about his feelings, and uses his powers a lot, even when not necessary. He frequently butts heads with blue oni teammate Kazura who is The Stoic, generally keeping his emotions in check and often appearing humorless (although he can be The Comically Serious). He only uses his powers when necessary. For extra points, Aoi wears his clothes casually and has a red tie hanging loosely, while Kazura dresses conservatively and generally wears dark colors.
Excel and Hyatt from Excel♥Saga. The anime fittingly gives Excel red hair and Hyatt blue hair. When they sing the opening theme song, Excel has a red microphone and Hyatt has a blue one.
In Bakuman。, Takagi and Mashiro; Takagi tends to wear red and is somewhat more excitable and temperamental, while Mashiro wears Blue and is more often level headed. On the other hand, when issues that influence whether the manga they are working on at the moment will get an anime come into play, Mashiro tends to be the one to get impatient and take risks while Takagi is more cautious. Similarly, Miura and Hattori, as Miura tends to lose his temper more easily than the much calmer Hattori does, as while Miura is cautioned to avoid letting artists see him lose his composure, it's noted that Hattori angrily reacting to Mashiro and Takagi going mainstream is unusual for him.
In Muhyo And Roji, Muhyo is a blue oni to virtually everyone he's partnered with. His old friend and current enemy Enchu comes off as fairly stoic most of the time, but inwardly held issues with jealousy and felt pressure to become an executor, leading him to snap and perform a Face-Heel Turn after his mother's death. Roji is also quite the Red Oni, being more impulsive, emotional, and concerned with others than Muhyo is. Busujima and Imai are another Red Oni, Blue Oni pairing.
Inverted in a A racing genre manga, Bakusou Kyoudai! Let's & Go!!, the older sibling, Retsu, wearing red, is level-headed and careful, while Go, the Hot-Blooded and bad behaving little sibling, wears blue. Their traits also show off in their customized mini 4wd racing machines.
Tomoe and Nanami of Kamisama Kiss. Nanami is red: passionate, energetic, frequently acts on impulse, very extroverted. Tomoe is blue: is very proud along with being much more calm, intellectual, tends to think before acting, and is more introverted.
Ryoga and Mousse in Ranma ˝, especially in their team-up episode to signify it.
Kaoru and Rei from Oniisama e.... Kaoru is sporty and sociable while Rei is reserved and angst-laden. Atypically, it's actually Kaoru who puts a leash on Rei, due to the latter's self-destructive habits.
Arikawa and Misaki from Hana No Mizo Shiru. Arikawa is cheerful, sociable and honest about his feelings. Misaki is quiet, antisocial and emotionally repressed. The Chapter 4 picturelampshades this trope, by outlining how both characters' birth flowers describe their personalities (Arikawa is honest and free; Misaki is delicate and sensitive).
Brothers Kanba and Shouma Takakura in Mawaru-Penguindrum are a classic example, with their hair colors being an instant giveaway. Kanba is the handsome, emotional, brash brother who usually takes immediate action, is popular with the ladies, and is determined to follow in their father's footsteps as the family protector. Shouma by contrast is practically a House Husband, being mellow, cheerful, cautious, and often the voice of reason and restraint to Kanba's hotheadedness.
Harunobu Nikaidou and Rei Kiriyama from Sangatsu No Lion have this dynamic, and it manifests in the way they approach shogi as well as in life. Nikaidou's passion, enthusiasm, and strong determination make him the Red Oni, while Rei's calm intellectualism and introversion make him the Blue Oni.
The case of Chuunibyou Demo Koi ga Shitai! is a bit complicated. Rikka's red to Yuuta's blue, yet when she's paired with her "servant" Dekomori, the latter's red to Rikka's blue.
Korean Web ToonThe Children's Teacher, Mr. Kwon has two students: the excitable blonde-haired, orange and blue-clad Kang San and the gloomy Eerie Pale-Skinned Brunette Cha Shiru, seen here. One has a weak heart and is the heir to a corporation and the other's a local boy with a dark past Kang San's the heir (who may not be heir to anything after the economic recession) and Cha Shiru's the local boy whose mother died in child birth and his dad blamed his son, went crazy, disappeared, and only returns to beat him to death (he's unsuccessful). If you didn't guess correctly don't worry, Mr. Kwon didn't either.
Infinite Ryvius: The Aiba brothers, Yuki (confrontational, defiant red) and Kouji (obediant, introverted blue). And Also Kozue (red) and Aoi (blue), though only by comparison. During Airs Blue's takeover of the ship's bridge, Fuu Nam Chai (red) and Stein Heigar (blue)'s incompatibility quickly becomes apparent.
This is played with in Xam'd: Lost Memories with the male lead Akiyuki and his school friend Furuichi. At first it looks like joker Akiyuki is the red oni while the more focused and serious Furuichi is the blue oni, but as they diverge from one another, the line between which is the red and which is the blue becomes more and more blurred, with Akiyuki maturing as he learns to harness his power and Furuichi slowly being driven insane by the hiruko inside him and his jealousy over losing their mutual friend, Haru, to Akiyuki. In the end, Furuichi's Xam'd form manifests as a bright red flaming monster, while Akiyuki's is shown to be a more neutral white with colored marking.
Marginal Prince has Alfred and Henri. The former is a Hot-BloodedFiery Redhead, while the latter is a stoicDeadpan Snarker and of course the two quarrel quite a lot over the course of the series. In one episode when Henri is abscent, everybody comments on how he's the one with the fixed role of snarking at Alfred's Large Ham moments. Naturally, their hair colors (Alfred = red, Henri = blue) respond to their roles too and bonus points also go for Alfred's nickname, which is, well, Red.
In Shiki the passionate doctor Toshio Ozaki pulls red oni duty while his lifelong friend, a melancholy monk named Seishin Muroi, plays the blue oni. Several of the important younger cast members exhibit this dynamic as well: among the girls there's excitable pink-haired Megumi (red) and her friend Kaori (blue) who has more neutral brown hair and a more reserved disposition. Kaori is also the blue oni to her orange-haired brother Akira's red oni. For the three main teenage boys, long-time antagonists Masao (red) and Natsuno (blue) have this dynamic, as lampshaded by their mutual friend Toru, who himself falls somewhere in between.
In Kämpfer the fiery Akane (when transformed into her Kampfer form) is a stark contrast to the "go with the flow" Natsuru Senō. Another possible match up is the lovely Shizuku Sangō (Blue) and the childhood friend Mikoto Kondō (Red) Interestingly enough in the series the concept is that the Red team and Blue team are against eachother (indicated by the bracelets) and have 1 Red Oni and 1 Blue oni on each.
Claymore has the main duo of Miria and Clare. From their personalities to their methods, these two are like night and day but when it's all said and done, they understand each other better than anyone else on their squad since both of their analytical skills and fighting power are nearly equal. They now fight in tandem with little to no communication needed between one another, managing perfectly synchronized attacks. As of late, some of Clare's recklessness has rubbed off on Miria, and likewise Miria's ability to lead and delegate team roles has rubbed off on to Clare.
Beta role falls to Helen and Deneve, who were like this from even before the story picked up.
Mei and Yako of Yurara are red and blue oni, respectively. Appropriately, Mei uses fire elemental powers, while Yako uses water.
In the first series, tomboyish and impulsive Minami is the red to cultured and reserved Aoi's blue.
In Twinkle, energetic Miria is the red to rational Sara's blue. Alma's Jewelpets Diana (who's playful and follows Alma's wishes without question) and Opal (who tries to reason with Alma) are another example.
In Sunshine, Kanon is loud and dramatic while her boyfriend/secret brother Mikage is polite and distant. There's also knucklehead Shouko and introverted Hinata. Class Representatives Nishigori (easily angered) and Opal (demure and caring) are yet another example.
Hot-Blooded Retsu and princely Blue Knight from Kira Deco are a textbook example.
Kill la Kill has siblings Ryuko Matoi as the red oni and Satsuki Kiryuin as the blue oni. Ryuko is brash, prone to letting her emotions get the best of her, and favours on-the-fly battle tactics rather than long-term strategy. In contrast, Satsuki is more of a calm and collected Chessmaster.
A variant of this occurs in Heat Guy J with Clair and Daisuke. The former is a bloodthirsty, volatile young mob boss with a Hair-Trigger Temper, who wears a purple shirt and tight-fitting black leather pants, whereas the latter is a cool, collected, laid-back detective who wears a blue undershirt and breezy white jacket and pants. The show also gives us, of course, Daisuke and the titular J, the latter of which is an android with all that implies.
Gundam Build Fighters has Sei Iori, a blue-haired responsible young man who's terrible at physical activities, and his friend Reiji, a red-haired goof off with amazing hand-eye coordination.
The sequel, Gundam Build Fighters Try, has Yuuma Kousaka, a blue-haired glasses wearing boy who specializes in long-range tactics, and Sekai Kamiki, a red-haired martial artist who specializes in barefisted brawls.