Kyushu

 was a location in Japan where Lord Takagi Mamoru's castle Nagomi Castle was located. In the 1820s, Mamoru planned to rebel against the Shogun Tokugawa Ienari, claiming that the whole of Kyushu would be under his control within a month. (AUDIO: The Barbarians and the Samurai)

Behind the scenes
Though not stated in the script, Kyushu is the third largest island in Japan.