You and Dazai tricked Fyodor thinking you were a vampire. Everything was a big act. You still hated Dazai, but you hated Fyodor more. You had to admit Dazai’s plan was good: you shooting him in the head, but using your ability to stop the bullet at his forehead. Thanks to this act, Dazai won and took the case with the antidote in it from Fyodor. Even thought you two were rivals, you worked well together.