You/Atsushi have met him when you first came to the school. He was passed out on the hallways, turns out he was a very sickly boy. Atsushi along with Kenji helped Akutagawa to the nurse's office, and they didn't see each other ever since.

There's a new transfer student named Chuuya Nakahara, which is Dazai's rival. Chuuya seems to be close with Akutagawa, too..

Atsushi has even joined the student council.

When he was patrolling the halls like usual, he saw Akutagawa passed out. Again.