Well as Kusari literally means chain, first thing that came to my mind is the Emperor, and his royal family, as in his ancestors and his children...kinda like a family <strike>tree</strike> chain.
Seeing as the person with the real power in Japan/Kusari is the Shogun (Shogunate japan is a little confusing, from what I understood, the Shogun could be compared to a military prime minister and the emperor simply the head of state). So now my question is, whats the link between the shogun and Kusari/chains?