In much of Asia, especially well known in Japan, blood types are seen to determine personalities. It's common in any series where it's All There in the Manual to list the blood type of all the characters. Incidentally, the practice started as a type of pseudo-scientific propaganda: One group of people rebelled against invasion while another simply accepted the invaders. Since the two groups had different blood-types, the army doctors simply claimed that it was their blood-types making them rebel, rather than accept that just maybe, most people don't like having their country invaded. Interestingly, there used to be machines in public places which would tell your blood type, but they were removed after the health issue associated with shared needles became more apparent.
It's said that the predominant blood type in Japan is A, with about 40% of the population, while Americans tend toward O, about 37%. It's also estimated that more than 99% of the Japanese are Rh+, so the familiar +/- seen after American blood types can usually be dispensed with.
This belief was also the basis for a Japanese eugenics program during WW2, and has since been disproven.
While the system above is almost exclusively an east Asian trope, Western media does occasionally use blood types as metaphors for a character's personality, especially assigning Type O- (Universal Donor) to generous, selfless characters.
Compare: Four-Temperament Ensemble.
- Kamiyama, Hayashida and Maeda from Cromartie High School try to deduce Freddy's blood type based on his behaviour. They presume him as a B-type by looking at his completely unpredictable movements (sumo teppo practice shows him to be an A type and holding a textbook upside down is considered either a B type or an AB type).
- The issue pops up in a chapter of Franken Fran, in which the school becomes obsessed with the theory to the point that it causes social splits and discrimination. This causes problems for Adorea, whose dominant blood type is constantly changing due to the sheer number of organs she stores in her body.
- Volume 6 of the Harukanaru Toki no Naka de manga includes a scene with Akane, Tenma and Shimon trying to guess the blood types of the Hachiyou based on their personalities.
- Several characters in JoJo's Bizarre Adventure have listed blood types.
- Jonathan Joestar is type A, fitting with his caring personality.
- Joseph Joestar is Type B, suiting his more playful personality and optimism, especially as a young man.
- Jotaro Kujo is also Type B, which is unusual considering his more subdued personality. But he definitely fits some of the "loner" bits of the type.
- Giorno Giovanna is the only Type AB main character, suiting his serious and introverted attitude.
- And there´s a One Piece entry. In a SBS Eiichiro Oda revealed the Straw Hats' blood types this way:
- Luffy is F (by extension, Jimbei too)
- Zoro is XF
- Nami is X
- Usopp is S
- Sanji is S (Rh-)
- Chopper is X
- Robin is S
- Franky is XF
- Brook is X
- Vivi is F
- Ouran High School Host Club has an absolutely hilarious scene where Kaoru and Hikaru convince Haruhi that Honey is actually evil to the core by pointing out that he has the same blood type (AB) as Kyoya. Haruhi immediately broke the Fourth Wall to apologize to any viewers with AB blood type.
- Episode 3 of Recovery of an MMO Junkie has a scene where Koiwai Sakurai asks if he's an A Type because he's such a stickler (he is), then uses his own O blood type to justify his glib antics. A disclaimer immediately appears, stating that personality have nothing to do with blood types.
- In Revolutionary Girl Utena, one episode has a tidbit where Nanami and her posse discuss the blood type-personality correlation. It reveals that, while their parents and Nanami have Type B blood, Touga (her Aloof Big Brother) has Type A, which should be impossible... it turns out that both of them were adopted. Although, due to how shaky things were getting between the two and the fact that she had been too young to remember, Nanami automatically assumes that just Touga was adopted...
- There's also this scene:
Utena: Himemiya, you're type-AB, right? Let's see, type-ABs are elusive and seldom reveal their true feelings, huh?
Anthy: And you're type-B, right, Utena-sama? Type-Bs are self-centered and prone to misconceptions....
Utena: Yeah, sorry, okay.
- There's also this scene:
- In Sketchbook many characters' personalities seem to fit their stated blood types. Hazuki Torikai (type A) is the straightest example, which is lampshaded several times in the manga. However, Sora Kajiwara (Type A) and Daichi Negishi (Type AB) are subversions, which is also lampshaded.
Daichi Negishi: I'M AB! DID YOU THINK I WAS B? BASTARDS! WELL I'M NOT! SORRY!
- The four main leads of Wotakoi: Love is Hard for Otaku each has a different blood type that corresponds to their respective personality stereotype.
- Kind and sweet Narumi is Type A.
- Laid-back and self-absorbed Hirotaka is Type B.
- Hot-Blooded but responsible Kabakura is Type O.
- Cool and independent Koyanagi is Type AB.
- Naoya averts this trope by being a Type AB despite being nice and happy-go-lucky like Narumi. However, Kou's shy and constantly apologetic personality fits her Type A blood.
- Zigzagged with Yugi Moto, who has type AB Negative blood. Cool, controlled and unforgiving aren't the best choice of words to describe him. They are, however, a good choice of words to describe his alter-ego Yami Yugi, who shares his blood type on account of sharing his body. Also, a sub-characteristic associated with AB blood type is Split Personality. Or an least mood swings. Which Yugi has. In spades.
- Bakura who also have a Split Personality is also type AB.
- Marik, despite also having Split Personality like Yugi and Bakura, is not type AB. However, his actual blood type (B) does fit his personality much better than AB. The fact that Marik's other half came from very different circumstances than Yugi's or Bakura's is probably why he's different.
- In Mad Max: Fury Road it's a major plot point that Max is a universal donor and his personality actually does match up quite well with most of the traits of Type Os described above.
- Discussed in South Korean girl group f(x)'s nu song NU ABO, where it describes a completely different personality symbolized by a nonexistent blood type called ABO.
- Is the whole theme of the Japanese song Blood Type Hamburger Shop, each verse featuring an employee exemplifying each blood type taking the orders of an unfortunate customer. Curiously, the verse for AB heavily downplays the "coolheaded" and "rational" bit despite mentioning it in-song, and is played more like an Absentminded Professor. Like many things, it is a subject of heavy Memetic Mutation on Nico Nico Douga, with many videos in various fandoms being created, matching up the characters with their corresponding blood type personality.
- The Bronze Horseman by Paullina Simons. After Major Belov is severely wounded during a river assault, his wife Tatiana, a nurse in the Red Army, saves his life by donating her own blood. Belov is told it's lucky she's a universal donor. Belov can only think with irony "Of course she is."
- In Kevin J. Anderson's Death Warmed Over, a halfway house for down-and-out monsters offers expired B-positive blood packs from hospitals to vampires in need. It's not a popular flavor, but the house's manager likes to reinforce the "be positive" message.
- House is type AB ("Universal Receiver"); Wilson is type O ("Universal Donor"). In this example, the Japanese personality types are completely ignored and it's brought up in-universe solely as a comment on House's tendency to take from anyone whatever he needs and Wilson's tendency to give to anyone whatever they need.
- As a Western game with Japanese influences, battle-girl lists its heroine's blood type among her vital stats. It's B, which suits her.
- The indie RPG Cthulhu Saves the World has Umi, one of the party members, bring this up as banter. Umi states that her blood type is B+, making her a cheery person. Unfortunately, the other party members are the Great Old One-turned-hero, a talking sword, a goth necromancer, an alien, a crazy priest and a demon-dragon. These members respectively have ink, nothing, Uranium, and acid. Not even two other human members can give expectable answers, as the old man is insane, and therefore cannot remember his blood type, and the necromancer, being Emo, says she's got pain for blood.
- Final Fantasy:
- Parodied for Mog from Final Fantasy VI - his official listed blood type is "black-footed duck."
- Shockingly, Cloud Strife from Final Fantasy VII fits the AB blood type 'personality' almost to a T. Guess which blood type he is.
- Same goes for Squall Leonhart from Final Fantasy VIII but not as hard like Cloud to have split personality. But, rather a "mask" to cope with his abandonment issues.
- In the Japanese version of Fire Emblem: The Blazing Blade, the elemental affinity of the tactician (an avatar for the player) was determined by both birth date and their blood type, both which could be manually chosen. In the international releases, since this trope doesn't have as much relevance, it was changed so that birth date was the sole factor in deciding affinity.
- In the Princess Maker games, stats are determined by blood type. And in 2, it also determines how stressed the girl gets; one notable aspect is that a girl with Type A blood will never smile.
- An early PA in Star Ocean: Till the End of Time gives the player the option of choosing Fayt's blood type. Each choice either raises or lowers the affection of certain party members, giving insight into what personality types they like and which ones they don't. Judging from Fayt's actual personality in the game, Type O seems to be his blood type by default (since the two that go up from this are Sophia (his childhood friend) and Albel.) To support the fact that he remains optimist throughout the game, agrees to almost everything and is very sociable to the point where he makes friends easily. Also, if the group were to ever get ambushed, he announces that "He was careless!"
- You can choose a blood type for the protagonist in Tokimeki Memorial Girl's Side games. It only affects the horoscope. All of the love interests have blood types listed as well.
- In Valkyrie no Bouken, you get to choose a blood type at the beginning. Whereas blood type doesn't establish your personality type, it does affect the rate at which you level up: A → normal, B → precocious, O → late-blooming, AB → random.
- In the H-Game Violated Heroine, you can customize the heroine's blood type at the beginning of the game to raise combat stats: A —> more Agility but less Spirit, B —> more Attack but less Defense, O —> more Defense but less Attack, and AB —> more Spirit but less Attack.
- A Simple Thinking About Blood Type is an anthology series that portrays the personifications of the four blood types and how they stereotypically react to various life situations. Type A is a law-abiding but considerate people-pleaser. Type B is carefree and outspoken. Type O is goal-driven but temperamental. Type AB is a rational individualist.
- In Blip, after the Friendly Neighborhood Vampire consumes several gallons of Type B blood, she suddenly shows an impulsive streak, and the author speculates in The Rant that this trope is in play.
- Discussed in the Miraculous Ladybug episode "Ikari Gozen". During the scavenger hunt, Kagami asks what Marinette's blood type is, expressing surprise when the latter doesn't know. Kagami then explains that she's a type O, and therefore is independent, optimistic, strong-willed, and intuitive. She then reasons that Marinette must be AB, based on her indecisive nature.
- It's blink and you'll miss it, but in the first episode of Futurama, just before Fry is about to get his career chip put in the first time, you see some of his info on a screen, where you can see that his blood type is B. Given his friendly and sunny if ditzy nature, it fits him well.