A collection of letters to one person from one person that show the slippings into insanity, like they start off as regular "so n so did this" "blank is getting on  my nerves" "I can't believe the amount of work I have" the usual but slowly the letters get darker as the person writing them gets more and more angry, slowly starting to threaten people, or commit crimes, at the end they write something along the lines of confessing to about to do a major and violent crime and you are left wondering what will happen to the characters, almost like they write "I'm coming for you, watch out" and then it ends. Idk it could be creepy or smth.