According to a BBC report, in Japan there is a "widespread belief that blood type determines personality, with implications for life, work and love."
When you meet someone new in Japan, you will most likely be asked "what blood type are you?" the same as Americans ask "what do you do?"
In fact, in 2008, four of out the top 10 selling books were devoted to the subject.
Matchmaking groups in Japan use blood typing as a criterion and there are actually speed dating groups set up so people can meet people with a certain blood type.
According to the BBC report, many Japanese believe that people with type A are "dependable, self sacrificing, but also reserved and prone to worry."
People with type O are decisive and confident.
People with type B are flamboyant free-thinkers, but selfish.
People with type AB? "Balanced, clear sighted and logical, but also high-maintenance and distant," says this report.
Interest in blood type and dating is so prevalent that women's magazines run articles about it, according to the BBC.
Some employers actually have asked about a prospective employee's blood type before deciding whether to hire him, which is much like some of the personality tests some companies give.
Even more interesting, there is actually a term for mistreatment because of your blood type, says this BBC report. "Bura-Hara" translates to blood group harassment.
Mari Yamaguchi, reporting for The Associated Press wrote this about blood typing:
"Matchmaking agencies provide blood-type compatibility tests, and some companies make decisions about assignments based on employees' blood types.
Children at some kindergartens are divided up by blood type, and the women's softball team that won gold at the Beijing Olympics used the theory to customize each player's training."
Another writer, Justin McCurry, wrote in The Guardian that there is a "darker side" to blood typology: "It has been blamed for bullying among kindergarten children, denying jobs to otherwise ideal candidates and ending happy relationships, all because of an imagined (blood type) mismatch."
Scientists don't give the theory that your personality and traits can be determined by your blood type. They classify it somewhere along the line as the same as horoscopes.
But there are enough people who believe in it.
According to the BBC report, Japan's last prime minister put his blood type (A) in his official profile on the internet.
And it looks like it will continue to be used as a matchmaking tool, so women can narrow down prospective mates.
During the speed dating session in the BBC report, the women were looking for men with blood type A or AB.
One woman told the BBC reporters that after dating a type B man, she was annoyed by how unorganized he was.
Her friend told the BBC that she is seeking a man with type A blood because she hopes that will mean the man is down to earth.