Assuming you're serious......in a number of Asian countries, it is a popular belief that a person's blood type is an indicator of their personality traits, similar to the way that astrological signs are in the West, and is often used to determine compatibility with a potential partner or for horoscopes.
(
Happosai _,,,,_(O ; o)_,,,,
Tue 20 Sep 2011, 15:20,
archived)