An elite samurai working for the Shogunate. Kariya has not drawn his sword in quite some time being that there hasn't been an opponent worthy of him in years, according to Goroujuu, a member of the Shogun's council who visits him. Upon learning of Sara's death, he determines that Mugen and Jin must be worthy adversaries, and brings himself out of retirement in order to face them. Although employed by the Shogunate, his truer motives are to use the government to further his own needs since the age of the samurai is ending.

(Source: Samurai Champloo Wikia)