I'm not well-versed in the late Edo Period, but Yamaouchi Yodo (Toyoshige) comes off as one of the more moderate figures involved in those events. He was a friend to Tokugawa Yoshinobu and had come out on the side of reforms within the Tokugawa shogunate and been placed under house arrest (along with Matsudaira Yoshinaga and others) as part of Ii Naosuke's Ansei Purge. He supported Yoshinobu throughout the crisis that came later and seems to have greatly distrusted the Shimazu's intentions.
I'd say the most famous activist from Yamaouchi's domain (Tosa Province) was Sakamoto Ryoma.