Kosuke Kurumizawa is the main antagonist of The 25th Ward: The Silver Case. He is an Observer who harnesses Kamui Uehara's power to attain a post-physical level of reality.
It is suggested by the characters that Kurumizawa attained this state through becoming an observer who could never be observed. By observing (and defining reality) without being observed (and thus never being defined in reality) Kurumizawa is able to cheat physical reality and live on as a "digital man" within the system of the cities and Kamui Uehara. He chooses not to die, and so he doesn't. Through this, he is able to exist in the "world of the dead" that other apparitions (such as Remnant Psyches) exist in. It is later revealed that Kurumizawa is also the "cursor" through which gameplay actions are performed by the player, and it is also implied that he is the running man controlled on the chapter select screen
