Talk:Tsukiyama family/@comment-24.149.42.183-20150705232440/@comment-10733658-20150705234416

Consanguineous marriages typically refers to marriages between First Cousins. (It isn't illegal in Japan, and has been fairly common in upper-class families throughout human history. But generally speaking, it's much less common these days.)

So basically, the Tsukiyamas as an upper-class family have a long history of marriages between cousins.