His first book on the subject, Ketsueki-gata de Wakaru Aisho (Understanding Affinity by Blood Type) became a best seller in 1971.
Blood-type research carried out during the 1920s and '30s in Germany,[3] ostensibly focused on how to recognise blood of non-Aryan origins during the newly emerging medical procedure of blood transfusions, resurfaced in "Age of Aquarius"-era Japan.
The book was hugely popular in Japan with the core idea of "blood type = personality type" becoming firmly embedded in Japanese popular culture and the cultures of other East Asian countries.
While seeming quaint and harmless, cases of Japanese workers finding themselves on the receiving end of workplace issues arising from being of the "wrong" blood type is common enough for the phrase "bura hara" ("ブラハラ"), an abbreviation of "blood harassment", to have been coined.
In addition, variety of personality decreases like type A to some extent compared to fresh vegetables.