is Shizuo's younger brother. He's a famous actor of extraordinary skills (praised as "unbelievable" ever since he first started out as an amateur) under the alias Hanejima Yuuhei. However, when away from works, Kasuka is completely devoid of emotion and rarely talks unless necessary - this attitude, according to him, is a direct influence of growing up with Shizuo, who abysmally lacks emotional restraints. Izaya's twin younger sisters, Kururi and Mairu, are his fans.
His loveLater, he falls in love with Hijiribe Ruri, whom he knows to be the serial killer Hollywood, after saving her twice: once when she was gravely injured by Shizuo, later when she was being hunted down by Nebula for her dullahan blood.