Like the Shinsengumi, the Mimawarigumi too was a special police force, created to restore order to Kyoto. The Mimawarigumi were made up of higher-ranking samurai and retainers who served feudal lords, as opposed to the Shinsengumi which consisted of ronin.
In Gintama, the Mimawarigumi appeared wearing opposite colors of the Shinsengumi.
Sasaki Isaburo (佐々木異三郎)
Sasaki Isaburo is the commander of Mimawarigumi, who shares his name with the leader of the real Mimawarigumi, Sasaki Tadasaburo (佐々木只三郎).