The Japan SAQ
Q. It seems like more than half of my female acquaintances over the age of thirty have the sound "ko" in their name, but there are very few Keikos and Yokos under the age of 30. Why is this?
"Ko" was originally used as an honorific in the names of many important people and scholars in ancient China, and came to Japan in the Nara period (710-794). It was used in the names of both boys and girls who came from important families and gradually became used more and more in female names. By the start of the Edo period, it was not used anymore for male names. It was also used by members of the Emperor’s family, and meant "noble woman" but in the early part of the 20th century, it became popular to add it to ordinary names in order to make them sound more impressive. It also took on the meaning of "child". For more than half a century, a majority of Japanese women had "ko" in their names, until it suddenly decreased in popularity during the 1980s. No one knows for sure why it fell out of favor, but since the trend coincides with a growing consciousness of the equality of women, it seems likely that mothers didn’t want to give their daughter a name that might make them sound childish and weak. Whatever the reason, names with "ko" in them sound quite old fashioned and are a very good way to tell which side of 30 a woman is on.