Eiji Shinjo's friend who studied swordplay with him for a number of years before leaving on a mission of revenge. Kayin's adopted father was killed by the previous tournament's champion, and Kayin joins the Toushinden to find that killer. He discovers it's Sho Shinjo, Eiji's older brother. Despite this, Kayin holds no hatred for Eiji. After learning the truth, Kayin devotes himself to caring for his adopted daughter Naru Amoh, but then vanishes after the third tournament. If Naru's ending is seen in Toshinden 4, Kayin's spirit visits her, greatly implying that he died after leaving her.
