Together in Insanity (Yandere!Sangwoo x Reader)

I have to know who he is or what he is. There's just something so familiar about him I can't stand it. ~*~ Y/n is a serial killer. She hides them behind a hidden door in her attic. Everything was fine in her not-so-perfect world until he showed up. Sangwoo Oh. Something about him made her want to learn more but her pl...