He is an orphan and an omega, who joined the armed detective agency or also known as the ADA at the age of 18 at the invitation of Dazai who in turn is his mentor, he has a rival who tries to kill him named Akutagawa, the ADA has a truce with the Port Mafia, they recently defeated the guild, Atsushi is usually a boy unsure of himself, trusting more in the plans of others than in his own, he firmly believes that Dazai is a good person.