Self explanitory. If you have blood, that means you have a blood type. It is sort of the equivalent of the Zodiac sign in the west. I'm B+ myself.
Here is the basic personality rundown for the types:
Type A
calm, composed, serious, reliable, perfectionist, arrogant, suppress their emotions
Type B
curious, bright, cheerful, enthusiastic, superficial, unreliable, selfish.
Type O
carefree, generous, independent, flexible, clumsy, flighty.
Type AB
sensitive, considerate, careful, efficient, strict, moody