You are Dazai’s friend, but you’re deaf. Even if it makes it a bit harder, Dazai still enjoys communicating with you immensely. You were a good friend, after all! He was still very energetic and expressive, but he tried not to be TOO over the top. Dazai was trying to learn sign language so you could communicate better than through notes or Dazai having you read his lips as he talked. He thought he finally learned it well enough, but unfortunately, he was still very far off.