Harry Potter and the Deathly Hallows tops the Japanese bestseller list for 2008. No surprise there. But in positions 3, 4, and 5 are three books from the Jibun no Setsumeisho series (Instruction Manual for My Self), and they are about about Type B, Type O and Type A blood types. (The list is here.)
You see, the Japanese believe that your blood type predicts your temperament, in the same way that your astrological sign might. Type O folk are outgoing; type A people are artistic; and type B people are independent. Bearers of type AB blood are a mixed bag and apparently not great readers.
You can find more on blood typing here, here, or here.–David E