There exists a common, popular belief in Japan and other East Asian countries that a person's ABO blood type or ketsueki-gata (血液型?) is predictive of his or her personality, temperament, and compatibility with others,similar to how astrological signs are used in other countries throughout the world, although blood type plays a much more prominent role in Japanese and the societies of other East Asian countries than astrology does in other countries' societies.
The ABO blood group system is widely credited to have been founded by the Austrian scientist Karl Landsteiner, who discovered three different blood types in 1900.
In 1927, Takeji Furukawa, a professor at Tokyo Women's Teacher's School, published his paper "The Study of Temperament Through Blood Type" in the scholarly journal Psychological Research. The idea quickly took off with the Japanese public despite Furukawa's lack of credentials, and the militarist government of the time commissioned a study aimed at breeding ideal soldiers. The study used ten to twenty people for the investigation.
In another study, Furukawa compared the distribution of blood types among two different ethnic groups, the Formosans in Taiwan and the Ainu of Hokkaidō. His motivation for the study appears to have come from a political incident: After the Japanese occupation of Taiwan following Japan's invasion to China in 1895, the inhabitants tenaciously resisted their occupiers. Insurgencies in 1930 and in 1931 resulted in the deaths of hundreds of Japanese settlers.
The purpose of Furukawa's studies was to "penetrate the essence of the racial traits of the Taiwanese, who recently revolted and behaved so cruelly". Based on a finding that 41.2% of a Taiwanese sample had type O blood, Furukawa assumed that the Taiwanese rebelliousness was genetically determined. The reasoning was supported by the fact that among the Ainu, whose temperament was characterized as submissive, only 23.8% had type O. In conclusion, Furukawa suggested that the Japanese should increase intermarriage with the Taiwanese to reduce the number of Taiwanese with type O blood.
Interest in the theory faded in the 1930s as its unscientific basis became evident. It was revived in the 1970s with a book by Masahiko Nomi, a lawyer and broadcaster with no medical background. Nomi's work was largely uncontrolled and anecdotal, and the methodology of his conclusions was unclear. Because of this, he was heavily criticised by the Japanese psychological community, although his books remain popular.
|Best traits||Earnest, creative, sensible, reserved, patient, responsible|
|Worst traits||Fastidious, overearnest, stubborn, tense|
|Best traits||Wild, active, doer, creative, passionate, strong|
|Worst traits||Selfish, irresponsible, unforgiving, unpredictable|
|Best traits||Cool, controlled, rational, sociable, adaptable|
|Worst traits||Critical, indecisive, forgetful, irresponsible, "split personality"|
|Best traits||Agreeable, sociable, optimistic|
|Worst traits||Vain, rude, jealous, arrogant|
Romatic Compatability by Blood Groups:
A is most compatible with A and AB
B is most compatible with B and AB
AB is most compatible with AB, B, A and O
O is most compatible with O, and AB
Discussion of blood types is widely popular in women's magazines as a way of gauging relationship compatibility with a potential or current partner. Morning television shows feature blood type horoscopes, and similar horoscopes are published daily in newspapers. The blood types of celebrities are listed in their infoboxes on Japanese Wikipedia.[A series of four books that describe people's character by blood type ranked third, fourth, fifth and ninth on a list of best selling books in Japan in 2008 compiled by Tohan Corporation.
Although there is no proven correlation between blood type and personality, it remains popular with the many matchmaking services that cater to blood type. In this way, it is similar to the use of astrological signs, which is also popular in Japan. Asking one's blood type is common in Japan, and people are often surprised when a non-Japanese does not know his or her own blood type.
It is common among anime and manga authors to mention their character's blood types, and to give their characters corresponding blood types to match their personalities. Some video game characters also have known blood types. In addition, it is common for video game series to allow for blood type as an option in their creation modes.
Blood type harassment, called "bura-hara" (wasei-eigo-a portmanteau of "blood" and "harassment"), has been blamed for bullying of children in playgrounds, loss of job opportunities, and ending of happy relationships.
There has been many incidents where people have been discriminated against their blood type. Employers have been asking blood types during interviews despite the warnings they have been given. Children at schools have been split up according to their blood type. National softball team has customize training to fit each player's blood type. Companies have assigning assignment according to their employee's blood type.
Facebook in many Asian countries allows users to include their blood type in their profile.
After then-Reconstruction Minister Ryu Matsumoto's abrasive comments towards the governors of Iwate and Miyagi  forced him to step down from his post, he partially blamed his behavior on his blood type, saying "My blood's type B, which means I can be irritable and impetuous, and my intentions don't always come across."
Blood types are very important in South Korea as well. An example can be seen in the film My Boyfriend Is Type B where a girl is advised not to date a man because his blood type is B. It is not uncommon to see Korean shows talk about blood types and personality seriously on national TV misleading the public as if it has some truth.
In Japan, a person’s blood type or ketsu eki gata is a popularly used to determine a person’s temperament, much the way Americans use astrological signs. The difference is that the Japanese take blood types very seriously. Japanese dating services use blood types to make matches. Employers use them to evaluate job applicants. High school students exchange blood types by way of introduction. Sports card include athletes’ blood types prominently alongside more traditional sports statistics. Manufacturers even market a wide variety of blood-type specific products, including calendars, chewing gum, colas, and condoms.
The obsession with blood types began in 1927, when a psychology professor by the name of Furukawa Takeji who work as a high school administrator began observing the the differences in temperament of the students who applied to his school. From his observations, he conjectured that all humans could be divided into two personality types. According to Furukawa, people with blood type A were mildly tempered and intellectual. People with blood type B were just the opposite – easily roused to anger and unintellectual. Furukawa published a series of articles and books, called “The Study of Temperament Through Blood Type,” which the public gobbled up, despite a complete lack of hard evidence. Interest in ketsu eki gata waned after Furukawa’s death in 1940, but was revived in 1971 when journalist Masahiko Nomi expanded on Furukawa’s theories in a best selling series of book, “Understanding Compatibility from Blood Types.” The new theories associated some blood types to academic success and different types of crime.
After Masahiko Nomi’s death, his son Toshitaka Nomi founded “Ketsueki-gata Ningen-gaku Kenkyusho,” the Institute of Blood Type Humanics. Since the Institute’s founding, interest in ketsu eki gata has continued to grow. It has been used to hire employees, divide labor forces into blood-type appropriate roles, broker marriages, and even dictate child-rearing techniques. It’s use has become so widespread, in fact, that some people have reported being discriminated against because of their blood type.
South Koreans in particular have embraced ketsu eki gata on the dating scene. No, you don’t need to get your eyes checked or opt for LASIK surgery. You did, indeed, read that correctly. Men with type B blood are reportedly having an increasingly difficult time finding dates. The men in South Korea must immediately be thinking “Houston, we have a problem” as soon as they find out that they are type B. In a recent nationwide survey conducted by a South Korean site, Type-B men were overwhelmingly voted the most difficult blood-type to date. In addition, forty percent of female respondents indicated that they would never marry a type B man. Magazines, television shows, and internet communities have all jumped on the band wagon, espousing the perils of getting involved with a type B man. There was chart-topping song entitled “Type-B Men” which featured lyrics describing these men’s short-comings, and even a hit movie, “My Boyfriend is Type B.” In the movie, the heroine, a type A personality, falls in loves a passionate but completely irresponsible type B personality, and, inevitably, hilarity ensue.
Type A: The Farmer
Speaking broadly, it is said that people with Type A Blood are calm, composed, levelheaded, and very serious. They have a firm character, and are reliable, trustworthy, and hardheaded. They are shy, introverted perfectionists. They are considerate to others and don’t easily lie. They are loyal to friends and coworkers. They can be secretive, though, and don’t often share their feelings. They try to suppress their own emotions, and because they have continual practice in doing this, they appear strong, when, in actuality, they have a fragile, nervous side, as well. They tend to be hard on people who are not of the same type, and consequently, tend to be surrounded with people of the same temperament. They also don’t hold their liquor well. Type A’s are the most artistic of the groups. They can be shy, cautious, conscientious, reliable, trustworthy, and sensitive. They can also be overcautious, picky, arrogant, and reckless when drunk.
Type B:The Hunter
People with Type B Blood are curious everything. That may be good, but they also tend to have too many interests and hobbies. They tend to get excited about something suddenly only to drop it again just as quickly. They seem to manage to know which of their many interests or loved ones are truly the most important. B Types tend to excel in things rather than just be average, but they tend to be so involved in their own world that they neglect other things. They have independent spirits with strong personalities. They have the image of being bright and cheerful, full of energy and enthusiasm, but some people think that they are really quite different on the inside. They also don’t really want to have much personal contact with others. While they don’t care what others think of them. They are extremely passionate about the things they hold dear. Type B’s are the individualists of the blood group categories and find their own way in life. Type B personalities can be curious, bright, cheerful, enthusiastic, independent, sensitive, and unpredictable. They can also be superficial, unreliable, selfish, unpredictable, indiscreet, lazy, and impatient.
Type AB: The Humanist
Type-AB people are an unpredictable, distant lot, but tend to use their heads over their hearts. They are good with money. Type AB’s are the split personalities of the blood groups. They are considerate of other people’s feelings and deal with them with care and caution. On the other hand, though, they are strict with themselves and those close to them. They, therefore, seem to have two personalities: one for those “outside,” and another for people on the “inside.” They often become sentimental, and they tend to think too deeply about things. AB Types have a lot of friends, but they need time to be alone and think things through, as well. They can be both outgoing and shy, confident and timid. While responsible, too much responsibility will cause a problem. They are trustworthy and like to help others. Type AB personalities can be sensitive, considerate, careful, and efficient. They can also be strict, moody, easily offended, critical, and standoffish.
Type O: The Warrior
Type-O people are outgoing, expressive, and passionate. They are highly motivated, natural leaders. Blessed with a strong physical presence, they aren’t afraid to gamble because they are so convinced they’ll win. Type O Blood people are said to set the mood for a group and to take on the role of creating harmony among its members. Their image is one of being peaceful and carefree. They are also thought to be big-hearted and benevolent, and they tend to spend money on others generously.They are natural athletes. They tend to be obsessive in their quest for success, and this can make them boring to others. Type O’s are outgoing, and very social. They are initiators, although they don’t always finish what they start. They appear to be levelheaded and trustworthy, but they often slip and make big blunders inadvertently. That is also the what makes O Types lovable. Creative and popular, they love to be the center of attention and appear very self confident. Type 0 personalities can be carefree, generous, independent, flexible, idealistic, goal-oriented, athletic, competitive, and adaptable. They can also be clumsy, flighty, jealous, greedy, unreliable, obsessive lover, vain loudmouths.
The popular indigenous typological system called ketsueki-gata holds that one can categorize people according to blood types A, B, AB and 0. This type of classification only dates back to 1927 when it was first proposed by Furukawa Takeji, a professor at Tokyo Women’s Teacher’s School.10 In this scheme there are four basic types (Table 3). Blood Typology has broad applications: a nursery school in Saitama used it to divide students into different groups, and Mitsubishi Electronics once relied on it when they put together product development teams composed of only AB blood types. One of the most interesting developments is the combination of western astrology with Japanese blood typology. This means that for each of the twelve zodiac signs there can be further elaborations made on the basis of ketsueki-gata, yielding forty-eight separate personality profiles. Almost every woman’s magazine now follows this syncretic practice.
Alternatively, the twelve western zodiac signs may be classified as one of four elements (Air, Earth, Water or Fire), and combined with the four Blood Types to produce sixteen categories. In one article, each of the sixteen combinations is accompanied by an individual “Love Biorhythm Graph.”" A paradigm chart also cross-references all the possibilities by sixteen male types, yielding 256 fortunes in a “You and your boyfriend’s love compatibility chart.” To illustrate, a woman who is a Water sign with Blood Type AB will do well with a man who is an Earth sign with Blood Type A, while someone who is a Water sign with Blood Type O should stay away from men who are Fire signs with Blood Type A.