血液型 (blood types)。

Last tea class, or just after, we talked about our blood type. Seems it's a thing in Japan to know people through their blood type (ketsuekigata), as it is here with the Zodiac. Wikipedia says that "blood type plays a much more prominent role in Japanese society than astrology does in the West". Here's that page's summary of traits:

	Good things	Bad things
A	Earnest, creative, sensible, reserved, patient, responsible	Fastidious, overearnest, stubborn, tense
B	Wild, active, doer, creative, passionate, strong	Selfish, irresponsible, unforgiving, unpredictable
AB	Cool, controlled, rational, sociable, adaptable	Critical, indecisive, forgetful, irresponsible, "split personality"
O	Agreeable, sociable, optimistic	Vain, rude, jealous, arrogant

Apparently it's also thought of as a measure of compatibility. And it's super popular: "A series of four books that describe people's character by blood type ranked third, fourth, fifth and ninth on a list of best selling books in Japan in 2008 compiled by Tohan Corporation." 信じられない.

So a bit ago I was waiting for someone else to do something here at work, so I practiced Japanese (and had some fun) with online dating profiles on Yahoo Japan. (The text one finds on sites like Yahoo is great for relatively easy reading.) And there it is: blood type! Will have to learn more about that.