
Was Ryu a part of the Date clan? I think he could be
In Kashimo's backstory, Ryu was mentioned to be living in Date province (its not a province but whatever). The Date clan is a samurai clan, and Ryu in the Edo period had a samurai cut and held a katana. Also, it would explain Uro's hatred more since the Date clan is related to the Fujiwara clan.
(Speculation/Headcanon part) we know nothing about the time Kashimo lived but since it's very far away from Date city I'd say he was in his prime at around the Shimabara rebellion, and participated in it (for some lore I'm working on)