Notes of Assassination

When I woke up, there was a gun and a note saying, "You know what to do." Who am I? Why do I feel so comfertable killing people?

I don't remember who I am. All I do know is that my purpose in this land is to kill whoever the note says. If I keep doing so, everything I need will be provided.

All I have is a gun, a knife, a lighter, and the darkness to help me kill and recover my past.