Blood types

There is a popular belief in Japan and Korea that a person's ABO blood type is predictive of their personality, temperament, and compatibility with others, similar to the Western world's astrology.

Blood type	Positive traits	Negative traits	Most compatible with
Type O	Social, outgoing, creative, popular, confident, speak their mind.	Don't always finish what they start, not dependable, like to be the center of attention	O is most compatible with O and AB.
Type A	Artistic, creative, trustworthy, stays calm in situations others panic, good at avoiding confrontation, polite, responsible, if there is a job to be done they want to take care of it themselves, seeks success.	Picky, sensitive, shy, sensitive, sometimes withdrawn, conscientious, stubborn.	A is most compatible with A and AB.
Type B	Mentally tough, individualist, finish what they start, focused, specialist in something.	Not cooperative, likes to follow their own rules, pay attention to thoughts more than feelings, can seem cold and serious.	B is most compatible with B and AB
Type AB	Outgoing (but also sometimes shy), confident (but also sometimes timid).	Split personality, so sometimes shy and sometimes outgoing, sometimes timid and sometimes shy, can't handle too much responsibility, unpredictable.	AB is most compatible with AB, B, A, and O.