My summary from Mr. Masahiko NOMI's book "Ketsueki-gata Josei Hakusho" (Blood-Type Woman White Paper).
There is a superstition that "type AB is a genius or fool". This is an expression that type AB is completely mysterious. Needless to say, this is untrue. Type AB is a person of common sense more than any other types.
The No.1 personality of type AB is the dual-facedness. One is to have competence and strength, and to participate in the society faithfully. The other is sudden feelings, unrealistic actions of capricious willfulness.
I'd like to point out the rational thinking for type AB's basic parts, too. This is seen coldhearted, when too much appeared in attitudes. This cooperates with type AB's trend to be less absorbed to things. Type AB has little sense of togetherness with the society or the group, even if it is zealous to take part in. This draws a clear line from Type O and A.
Type AB seems to participate in the society for getting safe and stable life. In fact, type AB hopes mental and economic stabilities most. It usually makes up its regular image (or mask) to join to the society. This resembles many students or employees usually wear their uniforms.
It can choose any images, but usually chooses soft and sociable one for smooth society participation. Many type ABs wear smiling and soft images.
As a result, men seem gentle although less manly, women seem famine in addition to gentle, which seems women got a little gain. But both are only superficial.
Although someone sees type AB as "dual personality", it is not right. Proof: type AB takes off its image easily, to the people who became a little bit familiar to.
Shigeyuki Yamaoka (2001), A Psychology Book for not to Become a Useless Adult
Self report of personality from 1 (strongly disagree) to 5 (strongly agree); Subjects are 649 university students who love blood-typical topics.
The above descriptions are correct, because I am type AB. First of all, distant feeling from the society is one of the type AB's fundamental traits. Therefore, it decided to make a good external image, because of little sense of togetherness with the society.
I recalled a tale of Japanese immigrants to the US. The "nisei" seemed to be more like American, to melt to American society smoothly for civil rights. Mr. NOMI also says "type AB takes off image easily, to the people who became a little bit familiar to." It depends. Some ABs easily take off their images while others do not. I am the latter.