It’s the final trial, and Shuichi (aka you) had a gut feeling that Kaede is the mastermind, so he was the only who voted for her. Which she is the mastermind, but she got corrupted by the despair in her heart. When Monokuma spilled the beans about the true mastermind, Kaede broke into psychotic laughter.

“Aw… Shuichi was the only one smart enough to realize that I was the one behind it all!” She said in a scary tone.