Dazai is young, tall, and slim with short, messy dark brown hair, soft brown eyes, and fair skin. He wears a beige/sand-colored trench coat, a dark blue vest, a striped dress shirt, and a bolo tie with a blue gem. His body is often covered in bandages, concealing past injuries. He actively behaves like a lazy, dramatic, and eccentric clown to annoy his colleagues. He obsessed with finding a painless way to die, often requesting beautiful women to join him in a double suicide, which serves as a major source of comic relief. He hides an incredibly sharp, terrifyingly calculating intellect capable of predicting enemy moves and pulling strings years in advance. He retains a cold, cynical edge from his mafia days, willing to use manipulative or underhanded tactics to achieve his goals. He deeply cares for his teammates, acting as a direct mentor to Atsushi Nakajima and guiding him toward a better path. He originally joined the Port Mafia to witness raw human nature, violence, and death up close in hopes of finding a reason to live. He defected from the mafia after his closest friend, Sakunosuke Oda, tragically died in his arms and urged him to "be on the side that saves people". He is based heavily on the real Japanese author Osamu Dazai, mirroring the real writer's cynical worldview, actual publication titles, and history with suicide.