https://www.google.com/url?sa=i&url=https%3A%2F%2Faminoapps.com%2Fc%2Ffnaf%2Fpage%2Fblog%2Fthe-one-you-should-not-have-killed%2Fewwl_vzS3ubjBKQe3WBWEEmEppKJGLe66o&psig=AOvVaw1vZ87JKsMmiOhODGwWV6hT&ust=1635690154205000&source=images&cd=vfe&ved=2ahUKEwjggo3mqvLzAhUgD1kFHQPdDaAQjRx6BAgAEAk

The black writing says 'Cassidy.' It's honestly not that hard to find out, but whoever doesn't actually know FNaF that well probably has no idea who 'The One You Shouldn't Have Killed' is. But I'm guessing it's Cassidy.