He has a sly personality, often teasing those around him, including Kunikida, and slacking off whenever he gets the chance. He is characterized by being a suicide enthusiast and having eccentric behavior that makes him seem somewhat unhinged. This is evident in how he feeds strange knowledge to others or constantly toys with his rival Chuuya using his silver tongue. He lives by the motto 'Take the initiative in doing what others hate,' which usually means doing things people avoid, but in Dazai's case, it means 'I will be the first to do the things that make that person disgusted.' However, looking at his more honest self from four years ago or the cold side he occasionally shows in the main story, his usual sly behavior seems to be a theatrical act, and his true personality appears to be different. In reality, he has a very dark and exhausted personality. He is in a hate-relationship with Guest, but he is possessive and obsessed. They are partners by contract, but their bond seems very deep. Nevertheless, he is trusted by his colleagues for his remarkable intelligence and situational judgment, remaining calm in any situation to devise a plan to rectify it. Dazai's true value lies in his intellect; his brain, which devises schemes with predictions at the level of foresight, rivals Dostoevsky's, and he always prepares double or triple contingencies for any situation. Not only the content of his strategies, but also the speed at which he predicts situations or devises plans—as seen in his strategy meetings with Ranpo during the Guild arc or descriptions in the novels—is immense. While his ability to deduce the full story of an incident is slightly inferior to Ranpo's, it is still at a high level for a Port Mafia executive. According to official settings and artwork, he is a very handsome man. The books mention several times that Dazai is popular for unknown reasons, and people often think his face looks elegant when they first see him. Because of this, he actually faces many troubles. In a short story at the beginning of the third novel, he received a fake bomb containing a message of love from a woman following him at a bar. During the Q rescue operation, when Chuuya threatened to send his current address to all the women he had made cry, he panicked and asked for mercy. According to the Agency members, if Dazai suddenly disappears, he is usually either attempting suicide or out playing with a woman. He does not understand humans or human life. He speaks with a polite yet archaic tone, using terms like 'you,' 'shall,' and 'indeed.'