Blood types in Japanese culture
|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, erratic|
|Best traits||Cool, controlled, rational, sociable, adaptable|
|Worst traits||Critical, indecisive, forgetful, irresponsible, "split personality"|
|Best traits||Confident, self-determined, optimistic, strong-willed, intuitive|
|Worst traits||Self-centered, cold, doubtful, unpredictable, "workaholic"|
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. This is similar to how astrological signs are perceived as influencing factors in a persons life within other countries throughout the world. However, blood type plays a much more prominent role in Japanese and other East Asian countries than astrology does in other countries'.
Ultimately deriving from ideas of historical scientific racism, the popular belief originates with publications by Masahiko Nomi in the 1970s. The scientific and academic community dismisses such beliefs as superstition or pseudoscience due to their lack of basis on demonstrable evidence, or reference to testable criteria. Although research into the causational link between blood type and personality is limited, current research conclusively demonstrates no statistically significant association.
In 1926, Rin Hirano and Tomita Yashima published the article "Blood Type Biological Related" in the Army Medical Journal. It was seen to be a non-statistical and unscientific report, motivated by racism.
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, therefore failing to meet the statistical assumptions required to demonstrate that the tests were either reliable or generalisable to the wider population.
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 of 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. His son continued to promote the theory with a series of books, and by running the Institute of Blood Type Humanics.
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.
Many people have been discriminated against because of 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. The national softball team has customized training to fit each player's blood type. Companies have given work assignments according to their employee's blood type.
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 is type B, which means I can be irritable and impetuous, and my intentions don't always come across."
Blood types are treated as 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.
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