Kenji Kawamoto, a Tokyo office worker who organizes various social gatherings in Tokyo as a hobby, has been busy organizing one particular holiday party this year. You could say it's in his blood.
"The success of this party is all I have been thinking of nowadays," the 42-year-old said excitedly, like a little child waiting for Santa's arrival. "We had a pretty large crowd last year too, but this year's should be even bigger. We have more than 100 people signed up for this event."
Kawamoto created a social group 13 years ago when he was new to the city, and he's been coordinating parties ever since.
"When I first came to Tokyo for my job, I had no friends and I wanted to meet people," Kawamoto said. "So I created a social group calling for people from the Kyushu region [of southern Japan] where I am from. The group kept getting bigger, and we now have other social groups with names like People Born in the '70s or People Living in North Kanto region [Tokyo vicinity]."
Which group is drawing the biggest crowd this year? "Oh, that would be the blood type group. This group kept growing this year and we saw many new members."
Japanese are often asked their blood type in various settings. Friends often try to guess each other's blood type or one may be asked to mention his or her blood type on a job application. In singles' bars, it can be a common question -- the Japanese equivalent of "What's your sign?"
Many Japanese people believe blood type is an indicator of everything from personality to marriage compatibility.
Japanese morning television shows and magazines often include horoscopes based on blood type and several books on blood type analysis came out during the last year, including one called "An Instruction Manual for Those With Type B Blood."
The book, written by an author who goes by the pen name of Jamais Jamais, became one of the nation's top sellers. The manual led to sequels for other blood types -- A, O and AB -- selling a total of 5 million copies.
"Blood type is a good tool to understand different human behaviors," said Chieko Ichikawa, the head of Human Science ABO Center in Tokyo. The center was founded by journalist Masahiko Nomi, who released a series of publications on blood type in the 1970s with a concept called blood type humanics -- a new way of studying the human mind.
"Most Japanese have some knowledge of each blood type and its trait so blood type often becomes a good conversation piece," Ichikawa said.
Most scientists don't see a basis for the nationwide fascination with blood types, at least for now.
"There does not seem to be any validity between blood type and personality or traits analysis," said Toshiki Nishizawa, a clinical psychologist in Tokyo. "Having said that, dating back to 400 B.C., the days of the Greek physician Hippocrates... people tried to study if or how fluids in our body such as blood can affect our personality."
Kawamoto's group called Association for Blood Type A.B.O.AB meets almost every month, with roughly 40 attendees at each gathering.
"This is just one way to meet new people and make friends," Kawamoto said.
And it's been a fruitful experience for some.
"We have 37 couples that met at those gatherings and got married," Kawamoto said. "I met my wife through group activities and we are the 22nd couple. We are both Type O and we have been getting along pretty well."
The blood type group and other social groups often meet for various activities such as barbecues in summer and cherry blossom viewing in spring.
"People sometimes use blood type analysis to see who may be a better match for them," Ichikawa said. "Such knowledge should be used only as guidance and not a definitive last word. But knowing one's blood type is like doing your homework. It may better prepare you when you meet a stranger or give some reasoning for the behavior of someone, which you may find hard to understand."
Takeshi Yoshida, another member of the group who married a fellow group member, said his wife, Ayako, surprised him occasionally when they first started to live together.
"I am Type A who is said to be a lot more detail-oriented than Type B, my wife," Yoshida said. "For example, when I hang laundry, say a handkerchief, I pull out the wrinkles and then fold it nicely before I hang it. This way I can just pick it up in the morning before I head off to work. My wife still hangs it as one big piece even though she realizes why I do what I do."
Yoshida understands every couple may go through similar experiences, and he said he sometimes finds himself referring to blood type analysis to understand differences between him and his wife.
"The widespread use of blood type analysis in Japan is not that surprising," said Ichikawa. "We have all four types spread out among the population -- 31 percent Type O, 38 percent Type A, 22 percent Type B and 9 percent Type AB -- so taking samples and analyzing them is much easier in Japan. In some parts of the world, like many countries in North America and Europe, a few blood types -- specifically Type O and A in this case -- make up a majority."
"Blood type analysis may give people a framework to help them understand society and people," the clinical psychologist Nishizawa said. "Having a frame of reference gives people peace of mind. This may reflect the state of our society -- uncertain and fluid. From job security to human relationships, many people do not know what to believe or where things are going ... and blood type analysis may just do that for them."
The Japanese have long studied and analyzed traits of human behaviors based on four blood types -- A, O, B and AB.
The study of blood types began in the early 1900s, soon after their existence was discovered.
Japanese scientist Takeji Furukawa published what is considered the nation's first book on blood typology in 1927. The nation's fascination with blood type and different behavioral tendencies grew with Nomi's extensive work in the field. Through his field work and observation, Nomi collected blood type data of more than 50,000 Japanese.
"Differences in the blood type composition can show unique traits or tendencies of people," Ichikawa said. "Our research has focused on Japan so far but it would be interesting to conduct research in those countries if we can collect enough data and samples to analyze."
Here are Ichikawa's descriptions of each blood type and some famous examples from the Human Science ABO Center:
Type O: Often seeks to make friends or form a group. Has great ambition for power and prosperity. Strives for leadership.
"Type O people are good at finding ways to satisfy basic human needs, meaning they have good survival instincts or skills," Ichikawa said. "They are keen to find out what their position, role or expectation is within a group. With that knowledge, they come up with ways to survive within that group."
Famous Type O's include Al Capone and Charlie Chaplin.
Type A: Methodical, organized and responsible. Self-restrained. Places importance on order, formality and stability. Sensitive to changes in surroundings or environment.
"Type A tends to think of oneself in relation to others and his/her surroundings," Ichikawa said. "They often pay attention to how their action/behavior can affect or relate to society."
Famous Type A's include Robert Kennedy and Meg Ryan.
Type B: Seeks freedom. Values independence and practicality more than community and order.
"Type B focuses on what he/she is interested in," Ichikawa said. "Other types may be driven by societal norms or morality but the driving force for Type B is the source of interest. This does not mean they do not pay attention to societal needs, but they often may be viewed as self-centered or unconventional."
Famous Type B's include Jack Nicholson and Johnny Depp.
Type AB: Rational thinker -- shows sometimes conflicting dispositions of Type A and Type B.
"Qualities of Type A and B often have a dialogue in the minds of Type AB," Ichikawa said. "They often seek balance between the two. This process is often not easily understood or recognized by others. So Type AB can be described as mystical or an owner of a split personality."
Famous Type ABs include John F. Kennedy and Marilyn Monroe.