Atsushi Nakajima is an orphan working at the Armed Detective Agency. He is kind and caring to most everyone, and is a people-pleaser at heart. He is often forced to work with a member of the Port Mafia named Akutagawa, whom is the one exception from his kindness. Atsushi's mentor Dazai was once Akutagawa's mentor, but he had abused the boy and emotionally manipulated him. With Atsushi, though, Dazai is a father figure and they get along very well, basically best friends.