Osamu Dazai is a tall, slim young man with mildly wavy, short dark brown hair and narrow eyes of the same color. His bangs frame his face, with a few strands falling at the center of his forehead.

Dazai’s usual attire consists of a long sand-colored trench coat, which he leaves untied, paired with a black vest over a light blue, striped dress shirt. A distinctive bolo tie—featuring a turquoise pendant and a brown ribbon—complements his outfit. He wears beige pants and dark brown shoes. Notably, Dazai’s body is almost entirely wrapped in bandages, leaving only his face, hands, and feet uncovered.

In his Port Mafia days, Dazai donned a black trench coat that extended below his knees. During this period, he also wore bandages over his right eye, and his right arm was often in a sling—suggesting injuries from his infamous suicidal tendencies. Eventually, he regained the use of his arm.

Dazai’s appearance occasionally changes to suit the context:

• Post-Cannibalism Celebration: He wears a formal suit during the Agency’s gathering.
• Yokohama Fog Incident: Dazai is seen in a white waistcoat over black long sleeves, paired with white pants and a brown tie. A lapel pin adorns his padded overcoat.
• Meursault Prison: After being arrested by the Hunting Dogs, Dazai is dressed in white prison attire.

Osamu Dazai is an enigmatic and multi-layered individual whose true intentions often remain concealed unless he chooses to reveal them. His complex personality has only been truly understood by a select few, most notably his late friend Sakunosuke Oda. Oda believed Dazai would forever “linger in the darkness,” as his unparalleled intellect and inner turmoil left him isolated from others. Oda also recognized that neither killing people nor saving them could fill the void of loneliness that Dazai himself acknowledged.

As a former Port Mafia executive, Dazai displayed an unrivaled aptitude for strategy and manipulation. His dark and foreboding façade earned him a reputation as one of the most ruthless and effective members of the Mafia, where he rose to become its youngest leader. At the height of his tenure, Dazai contributed to nearly half of the organization’s profits over two years, but his methods left a legacy described as “dark as the Mafia itself.” Dazai’s sinister nature was evident even in his later years; when Kyōka Izumi expressed remorse for having killed 35 people, he coldly remarked that such a number was insignificant.

Dazai was notorious for his cunning and confidence. He devised long-term strategies to subdue enemies, including luring Mimic operatives—trained soldiers—into an elaborate trap. He was a master manipulator, skilled in persuasion and interrogation, often breaking subjects through psychological tactics rather than brute force. Despite his brutality, Dazai admitted to joining the Mafia in search of exposure to death and violence, hoping to uncover the essence of human nature and, ultimately, a reason to live.

Following Oda’s dying request for him to “be on the side that saves people,” Dazai defected from the Mafia and began working underground before joining the Armed Detective Agency. While his darker traits linger, his actions now align with a mission to protect others and maintain peace in Yokohama.

Agency Life

Within the Agency, Dazai contrasts his dark past with an outwardly lazy and comedic demeanor. He is frequently scolded by Doppo Kunikida for shirking responsibilities and slacking off. Despite this, Dazai’s intellect and sharp wit shine through, as seen when he deduced that Atsushi Nakajima was the tiger he believed was stalking him.

Dazai is often overly dramatic and enjoys teasing others for amusement, though this lightheartedness masks his deeper struggles. His infamous suicidal tendencies, played for comedic effect, stem from a profound existential despair. He frequently attempts bizarre methods of suicide but abandons them when they prove too painful. Dazai’s macabre humor includes his wish to commit a “double suicide” with a beautiful woman, a recurring joke that belies his darker outlook on life.

Duality of Character

Beneath his lighthearted exterior, Dazai retains the calculating and strategic mind that defined his Mafia years. He devises intricate plans, often withholding details until the opportune moment. He is also unafraid to use morally ambiguous methods to achieve his goals, such as manipulating allies or exploiting vulnerabilities in enemies.

Despite his flaws, Dazai deeply cares for his teammates, particularly Atsushi, whom he sees as having immense potential. He orchestrates collaborations between Atsushi and Akutagawa, envisioning them as a “new generation of Twin Dark” capable of confronting the city’s growing threats. His loyalty to the Agency and his commitment to its cause reflect his desire to honor Oda’s final wish and prove that even someone as morally ambiguous as himself can choose a better path.

Dazai’s duality—a mix of darkness and redemption—makes him one of the most compelling characters in the series, embodying the struggle between despair and hope.

No Longer Human (人間失格, Ningen Shikkaku) is Osamu Dazai’s Ability, granting him the power to nullify other supernatural abilities upon physical contact. This ability is always active, requiring only skin-to-skin contact to take effect.

Due to its passive nature, Dazai can neutralize abilities even while restrained, as long as the opposing Ability comes into contact with him. This makes him an invaluable asset in combat and conflict situations, as his power effectively renders opponents’ abilities useless. “No Longer Human” serves as a reflection of Dazai’s complex character, mirroring his detachment from the world and his search for meaning.

Intelligence

Dazai’s intelligence is his most defining attribute, serving as a cornerstone of his success both as a former Mafia executive and as a detective for the Armed Detective Agency. Ōgai Mori, a brilliant tactician and leader of the Port Mafia, regarded Dazai as his most capable right-hand man and deeply valued his strategic acumen. As a detective, Dazai is recognized alongside Ranpo Edogawa as one of the Agency’s “Double Jade” (双璧, Sōheki), a title highlighting his unmatched analytical prowess.

Dazai’s intellectual abilities enable him to match wits with formidable adversaries like Fyodor Dostoevsky, a master of cunning who views Dazai as his equal. Even Ranpo, who prides himself as the world’s greatest detective, acknowledges the parallels between Dazai and Fyodor, admitting that dealing with Fyodor feels akin to facing Dazai himself. Dazai’s ability to foresee outcomes and manipulate events to his advantage is one of his most formidable strengths.

Negotiation Skills

Dazai is a master negotiator, capable of persuading even his staunchest opponents to bend to his will. His achievements include:

• Convincing Kōyō Ozaki, a Mafia executive, to allow Kyōka Izumi’s arrest and eventual integration into the Agency.
• Gaining the cooperation of Francis Scott Key Fitzgerald, a former enemy, in the effort to capture Fyodor Dostoevsky.
• Persuading Ryūnosuke Akutagawa to tail and assist Atsushi Nakajima—his sworn rival—during the looming Decay of the Angel terrorism threat.

Dazai’s knack for manipulation extends to his allies as well. For example, he outwitted Naomi Tanizaki and thwarted a covert scheme devised by Kunikida that involved tricking him, proving his ability to anticipate and counteract even internal plots.

Dexterity

Dazai exhibits remarkable dexterity, showcasing an impressive aptitude for tasks requiring precision and finesse:

• Picking locks with ease, including handcuffs and locked containers.
• Planting a tracking device in Higuchi’s pocket undetected.
• Stealthily stealing Chūya Nakahara’s knife without being noticed.
  Kunikida once described him as “frighteningly dexterous,” capable of tasks like cracking a bank’s safe with a needle or seamlessly swapping slips of paper with fake ones.

Physical Prowess

While Dazai’s physical combat skills are relatively average compared to the physically adept members of the Port Mafia, he compensates with strategic timing and his Ability,No Longer Human. He has briefly held his own against Chūya Nakahara by predicting and countering his moves, though he was eventually overpowered. Dazai is resourceful in fights, using his environment to gain an advantage, though his physical limitations often lead to him being overwhelmed.

Heart Rate Manipulation

While imprisoned at Meursault, Dazai demonstrated the ability to manipulate his heart rate using a device implanted to monitor his vitals. By altering his pulse, he was able to encode and transmit messages digitally, showcasing his ingenuity even under restrictive circumstances.

During his tenure as an executive in the Port Mafia, Osamu Dazai amassed a notorious criminal record, which included 138 counts of conspiracy to commit murder, 312 counts of extortion, and 625 counts of various forms of fraud, among numerous other offenses. His involvement in these crimes solidified his reputation as one of the most dangerous and calculating figures in the organization.

However, after Dazai’s defection from the Mafia, he went into hiding, distancing himself from his dark past. In an effort to erase any trace of his criminal history, the Seventh Agency—a covert organization employed by Ango Sakaguchi—succeeded in wiping his record clean. This allowed Dazai to start anew, though his past still looms over him as a constant reminder of the darkness he once embraced.

The given name Osamu (治) carries the meaning of “govern” or “rule,” often symbolizing leadership or authority.

The surname Dazai (太宰) is composed of two kanji: 太 (ta or da), meaning “thick” or “great,” and 宰 (zai), meaning “rule” or “governance.” Together, the surname can be interpreted as “great ruler” or “one who governs with authority,” which may reflect aspects of his powerful and influential role within the Port Mafia.