Dazai mentioned early on why it’s so important for Oda to hold onto his rule of no killing even as others continuously threw insults of weakness. It was all in means to preserve his last piece of sanity and humanity which left him once he came back to a horrific scene at the result of intimidation for Gide’s end goal. It doesn’t stop there as this whole situation became a domino effect into Dazai leaving Port Mafia and taking a step into the light at the request of his dying friend.