Kou and Shi Clans

The double bar means marriages. Previous=previous head of clan.

Yuri is Shouka, Reishin, and Kurou’s first cousin once removed. A first cousin once removed is the child of one’s first cousin. So Yuri’s first cousin is Shouka’s father. In other words, you are someone’s cousin if you both have the same person as your grandparent. You are someone’s first cousin once removed if the same person is your grandparent, and the other person’s great-grandparent.

This means, that if we consider Kouyuu to be Yuri’s child, he would be Shuurei’s second cousin once removed (and Shouka’s second cousin). However, since we would then also be considering him Reishin’s child, then he would also be Shuurei’s first cousin (and Shouka’s nephew). This is what happens when you marry your relatives.

Ran Clan and Shiba Clan

Shiba Jin and Jyuusan-hime are second cousins. Gyokuka is Setsuna’s wife who hasn’t appeared yet in the anime. Confusingly, she and Gyokuka have similar names. In both names, Gyoku=jewel 玉. The kan in Gyokukan 環 means ring or wheel. The ka in Gyokuka (華) means splendor or flower.