To kill them and take their blood?
All i know is i have a rare type (idk what it is) because they had a hard time finding someone to match for a transfusion :p

wiki Wrote:Cultural beliefs

The Japanese blood type theory of personality is a popular belief that a person's ABO blood type is predictive of their personality, character, and compatibility with others. It was a serious scientific hypothesis which was proposed early in the 20th century, which gained currency within the Japanese public. This theory has long since been rejected by the scientific community. (For a proponent, see Masahiko Nomi.) This belief has been carried over to a certain extent into other parts of East Asia, including South Korea and China. In all these places, asking someone their blood type is considered as normal as asking their astrological sign. It is also common for Japanese-made video games (especially role-playing games) and manga series to include blood type with character descriptions.