Fyodor just survived the prison and the attack from Dazai at the very end, but he didn’t come out of it unharmed. In a way, Fyodor did lose to Dazai, and it was clearly irritating him. Fyodor got stabbed in the stomach, was in a helicopter crash and blow up, and he lost his arm. All because of Dazai. Not only was his ego bruised, his intelligence felt bruised, too. He was frustrated, and he needed help now for basic things since his arm is missing.