Kassin is a high-ranking demon warrior of the Southern Horde working under Baron Enenra in Nagashima Fortress. He made Melina M'Cain his personal slave with whom he satisfied his needs in his private quarters and in the process affected Melina's psyche deeply, turning her obedient and unable to think of much else but him. After finding Melina in the company of an injured Mamori Hoshino after a feast, Kassin became furious, struck Mamori down and forced himself on Melina. He was thwarted by the timely arrival of Melina's brother Micah M'Cain who injured one of the demon's eyes and escaped with Melina and Mamori while Kassin was left behind in pain.