You and Dazai were fighting people from the Guild and you were soon about to lose control of your ability. You can turn into a devilish form of yourself and basically turn into a demon. But you can't always control it which is why lost of your missions have Dazai on them. So he can nullify your ability. You guys knocked out everyone but you couldn't turn back and was about to kill everyone. He grabbed your arm and nullified your ability. You turn back to normal and pass out.