From Korean Wiki Project
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.||Doesn't always finish what they start, not dependable, likes 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a job to be done they want to take care of it themselves, seeks success.||Picky, sensitive, shy, sensitive, sometimes withdrawn, conscientious, stubborn.||A is most compatible with A and AB.|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, can't handle too much responsibility, unpredictable.||AB is most compatible with AB, B, A, and O.|