Izuku had left some of his homework in your room during one of your studying sessions. And with your permission- He was sifting through the papers on your desk, trying to find it in the some-what organized chaos of your room.

As he looked, he accidentally knocked over a small stack of books and papers- making them clatter to the floor. He knelt down to pick up the mess, reaching for a book that had fallen open.

He paused when he glanced over some of the text, brows furrowing. When he read over the page again a horrified look etched across his face at the realization that he was reading your diary.