Kousuke is a Special Class Investigator and a former partner of Kureo Mado prior to a major assignment in China. He was previously assigned to the 20th Ward as the partner of Seidou Takizawa and worked on the Gourmet case. He's devoted to the mastery of quinque and is said to have surpassed Kureo.
Currently, he serves as a member of the illustrious S3 Squad.
(Source: Tokyo Ghoul Wikia)