The Letters I Don’t Remember Writing

The first letter arrives on a quiet morning, written in the protagonist's handwriting but dated thirty days in the future. Inside is a warning about a moment that hasn't happened yet. Then a second letter arrives. And a third. Each one is more desperate. Each one reveals a truth the protagonist doesn't remember. Each one hints at a future they may not survive. The letters describe events that later come true-conversations, small accidents, choices that lock into place exactly as written.
But the final line of every letter is the same: "Stop me before I finish this." As the protagonist tries to uncover who-or what-is sending the messages, they begin to experience memories that aren't theirs, injuries that appear overnight, and time skips that leave them disoriented and afraid. Someone is rewriting their life. Someone who knows their thoughts, their past, their future. Someone who shares their handwriting. And the newest letter contains something far more terrifying than a warning: It contains a confession.