Talk:Kaneki Ken/@comment-3173617-20150622023314/@comment-10733658-20150622041229

I'm with Blue Luna, it really isn't surprising. Japan (and many other countries) don't have the same strong Taboo against cousin marriages that you see in some Western nations. And for much of history, it was not only perfectly acceptable but considered a good thing especially among the upper class.

(For example, Ciel from Black Butler is engaged to his cousin. One of the potential love interests in Sword Art Online is Kirito's cousin. It pops up in anime all the time.)

Though it does sound like the Tsukiyama family tree is small enough that it caused them some issues. That's a fairly common issue among nobility in many countries, as cousin marriages were very common to protect inheritance rights and keep the bloodlines "pure".