There is a popular belief in Japan

Japan

Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...

, Korea

Korea

Korea ) is an East Asian geographic region that is currently divided into two separate sovereign states — North Korea and South Korea. Located on the Korean Peninsula, Korea is bordered by the People's Republic of China to the northwest, Russia to the northeast, and is separated from Japan to the...

, and other Asian countries that a person's ABO blood type

ABO blood group system

The ABO blood group system is the most important blood type system in human blood transfusion. The associated anti-A antibodies and anti-B antibodies are usually IgM antibodies, which are usually produced in the first years of life by sensitization to environmental substances such as food,...

 or is predictive of his or her personality, temperament, and compatibility with others, similar to how astrological sign

Astrological sign

Astrological signs represent twelve equal segments or divisions of the zodiac. According to astrology, celestial phenomena reflect or govern human activity on the principle of "as above, so below", so that the twelve signs are held to represent twelve basic personality types or characteristic modes...

s are used, though blood type plays a much more prominent role in Japanese society than astrology does in the West.

Ultimately deriving from ideas of historical scientific racism

Scientific racism

Scientific racism is the use of scientific techniques and hypotheses to sanction the belief in racial superiority or racism.This is not the same as using scientific findings and the scientific method to investigate differences among the humans and argue that there are races...

, the popular belief originates with publications by Masahiko Nomi

Masahiko Nomi

Masahiko Nomi was a Japanese journalist who advocated Takeji Furukawa's idea of an influence of blood type on personality. He was also known as a sumo essayist....

 in the 1970s.