On the surface, Dazai is an irresponsible, insouciant detective. His intelligence is quickly revealed from behind his masquerade of stupidity, however. He is exceptionally intelligent and manipulative. His screwy behavior will often, but not always, be a part of a larger scheme.
The closest friend Dazai has had was Sakunosuke Oda, another mafia executive. Oda has come the closest anyone has come to fully understanding Dazai. Because of this, Dazai has a deep loyalty to Oda, even after his death.
Dazai is revealed to have an exceptionally negative, potentially nihilistic, view of reality. He feels lonely and in the dark at all times. This gives him a detached side. Dazai will often switch between his playful, offbeat display and his stoic, pragmatic side. He also has no sense of good and evil. He only "redeemed" himself because of the wishes of his late friend, Oda.
He is also maniacally suicidal, likely a cause of his nihilism. He sees death as an escape from the world he doesn't feel fits him. He's attempted suicide countless times, to the point where no one that knows him takes it seriously. His dream would be to commit double suicide (shinjū) with a beautiful woman.
He is almost maniacally homicidal at times. He shot an already downed corpse a few more times because of his demented personality. He has also killed countless people and doesn't feel particularly remorseful because of it (at least not apparently).
His unique outlook results in him being exceptionally hard to understand. His true motives are almost impossible to figure out in any given situation, and he's generally very mysterious. This unreadability has given him an edge over his enemies in intrigue battles.
Despite all this, Dazai is often the main source of comic relief in the series. His suicidal tendencies are usually played for comedy.
Dazai, for some reason, possibly his hysteria, grew up away from society. He had attempted suicide as far back as age 14. Ougai Mori, being an underground doctor working for the mafia, had taken him in as a patient after his suicide attempt. Coincidentally, Ougai was planning to kill the current leader of the Port Mafia and take the role himself due to the leader's late-life mental illness that was leading to the mafia to ruin. The same night he took him in, Ougai had killed the leader with Dazai as the only witness. Ougai told Dazai to cover his murder by saying the leader had died of natural causes and his final wish was for Ougai to succeed him. Ougai had taken Dazai in as his ward and they developed a casual relationship. Dazai had developed to be much more than Ougai had expected, intimidating Ougai. He had been much more dangerous than Ougai had thought.
Dazai had worked his way to becoming an executive of the Mafia. During his time, he had become a legend for the mafia. He had the most successful missions out of anyone in the mafia at the time. Ougai Mori stated that he wouldn't be surprised if Dazai killed him and took his position with how manipulative Dazai was being. He was also skilled at using torture methods to get information out of anyone.
Dazai had extensive adventures during his reign as an executive. He had become a partner with Chuuya Nakahara and they took out an entire enemy organization overnight. He had participated in the locking up of Yumeno Kyusaku that had resulted in mass casualties for the mafia. He trained Akutagawa Ryuunosuke extremely harshly, making him an exceptionally powerful executive. He had developed a friendship with Ango Sakaguchi and Oda Sakunosuke through the Port Mafia towards the end of his reign.
In a conflict with an enemy organization known as Mimic, Oda was killed and Ango Sakaguchi had been revealed to be a double agent. Oda's dying wish was that Dazai would become a better person. That's what lead him to join the Armed Detective Agency and eventually redeem himself.
- No Longer Human (In Japanese: 人間失格, Ningen Shikkaku): Dazai's special ability. It allows him to nullify any special ability by touching either the bearer of the ability or the ability itself. He is also immune to direct ability attacks because of this.
- Enhanced Physical Characteristics: Dazai has been shown to have exceptional reflexes, durability, speed, and strength.
- Master Manipulator: Dazai can predict his enemies and develope extremely intriquite schemes due to his intelligence.