I was reading the historical shoujo manga title Kaze Hikaru (which I mentioned at the end of this post), and in volume 14, p. 85 of the Viz edition, it's stated that the wife of Commander Kondo Isami of the Shinsengumi is "the eldest daughter of a Shimizu house general. She serves as a secretary for the Hitotsubashi house." A footnote explains that the Hitotsubashi house was one the Gosankyo, or three branches of the ruling Tokugawa clan. (The Gosankyo consisted of the Tayasu, Hitotsubashi, and Shimizu branches of the Tokugawa, and were descended from the eighth Tokugawa Shogun, Yoshimune.)

So our beloved Shimizu-san might be descended from a very old and powerful samurai family! Which does not surprise me--she certainly has enough strength and determination to be a samurai woman. Heh heh, a Shimizu ancestor could have been in Fuyu no Semi! ^_^ Kikuchi and Mochimune also have surnames from old samurai clans as well.