BLOOD TYPE THEORY
The blood type theory of personality is a popular belief in Japan. It states a person's ABO blood type, or "ketsueki-gata" is predictive of their personality, temperament, and compatibility with others, similar to the Western world's fascination with astrology. This belief has carried over to some extent in other parts of East Asia such as South Korea and Taiwan. This theory is completely dismissed by many scientists as superstition or pseudoscience. Even if you don't scientifically believe it in, I think the theory that blood and personality being related is incredible and can be very appropriate for certain individuals. Seeing that Tifa is not a real person, it could be that the Japanese creators incorporated this theory into their designs for each character, giving them a distinct blood type to match their personality.
Tifa has type B Blood and according to the theory, Type Bs are said to be loners and self-sufficient, as "hunters". Traits may include:
Dislike restrictions and one's own way, Non-stereotyped action, Non-stereotyped thinking, Self-conscious and not warped expressions, Makes less
distinction of things, Not conscious of circumstances, does no't care about social rules and customs. Traits also include being:
Creative, passionate, animal loving, optimistic, flexible and individualistic but at times
Forgetful, irresponsible, and self-centered. Famous people with type B blood include
Akira Kurosawa, Jack Nicholson, Luciano Pavarotti, Tom Selleck, Mia Farrow, Paul McCartney, Leonardo DiCaprio
and Vince Young.
I believe that this blood type suits Tifa well because she is a very passionate woman with optimistic beliefs. She is also extremely individualistic. However, I don't see her as ever being self-centered or irresponsible. If anything she tends to be extremely selfless because she cares so much about the world and those around her. It could be argued though that she was once self-centered as a child and teenager. Her relationship with Cloud in a way is selfish because she seems to put it aside out of fear or some other issue which then results in her focusing on something else that she may consider to be more important. Who knows.
Why So Popular in Japan?
Blood type was a contentious issue in the 1920’s and 30’s. The interest in blood types in Japan grew as a reaction against Western racism. Scientists in the west found that type B was common in Asia, but rare in Caucasians. As type B was typical in animals, they argued that Asians were inferior, lower on the evolutionary scale. Japanese scientists were keen to disprove this ludicrous theory, debate continued and it became a popular “ology.” Interestingly, 90% of the Japanese know their blood type, although whether this is the reason the fad became so popular or a consequence of its popularity is not certain. In contrast, their European and American peers are blissfully unaware of not only their blood type, but also the “blood typology” phenomenon.
Sian Thatcher, Japanvisitor.com