Osamu Dazai

Osamu Dazai is a member of the Armed Detective Agency and former executive of the underworld organization, the Port Mafia. He has the Ability No Longer Human.

Dazai is a young man with mildly wavy, short, brown hair and narrow dark brown eyes. His bangs frame his face, while some are gathered at the center of his forehead. He is quite tall;; and slim in terms of physique.

For his attire, Dazai wears a long sand-colored trench coat, the belt of which he leaves untied. Under it is a black vest over a striped dress shirt that is light blue in hue. He wears a bolo tie, which is held by a brown ribbon and a turquoise pendant. He also dons beige pants, dark brown shoes, and has bandages wrapped around his entire body; only his face, hands and feet are left uncovered.

Back when he was in the Mafia, Dazai wore a black trench coat that reached under his knees. He also wore bandages over his right eye and his right arm is in a sling—presumably products from his suicidal pastimes. At some point, he was able to regain use of his arm.

After the cannibalism, Dazai wears a formal suit during the Agency’s celebration.

During the Yokohama fog incident, Dazai wears a white waistcoat over black long sleeves and a brown tie, together with white pants. A lapel pin can also be seen attached to his padded waistcoat.

After being arrested by the Hunting Dogs and taken to Meursault, Dazai is currently wearing white prison clothes.

Dazai is a mysterious person, his true intentions are never revealed unless he reveals them. The person who got closest to the truth of his personality, as acknowledged by Dazai himself, was his friend Sakunosuke Oda, who recognized Dazai shall linger in the darkness forever, as there was never nothing that can surpass his mind. Regardless whether he is on the side of killing people or saving them, Oda knew that no place in the world could fill Dazai's loneliness, which Oda thought Dazai knew in himself. Regardless whether he is on the side of killing people or saving them, Oda knew that no place in the world could fill Dazai's loneliness, which Oda thought Dazai knew in himself.

In addition, Dazai kept an enigmatic and dark façade, whose endeavors in the Mafia were unrivaled and eventually earned him the status as the youngest leader in the history of the Mafia Because of his aptitude despite his youth, Dazai contributed to about half the Mafia's profits for at least two years. Eventually, Dazai's ledger became tainted; Ichiyō Higuchi describes his blood to be "dark as the Mafia itself". Even in his adulthood when he becomes an Agency member, when Kyōka Izumi showed remorse over having killed 35 people, Dazai remarked with a sinister face that such number is nothing.

As a saying in the Mafia went, "The greatest misfortune for Dazai's enemies is that they are Dazai'senemies", for Dazai was aptly described to be "practically born to be in the Mafia". He was extremely confident and was a terrific planner, coming up with long-run strategies to subdue his enemies. For instance, he was able to lure Mimic operatives, who were previously trained soldiers, to fall under his trap. Dazai is quite skilled in persuasion notably through his words, which he appeared to utilize in interrogations that broke targets who did not divulge anything under Kouyou Ozaki's torture squad.

Behind this grim persona, Dazai admitted that he joined the Mafia to be exposed to death, violence, and people giving in to their urges and desires, expecting that—in this way—he would be able to see the inner nature of humankind firsthand in hopes of finding a reason to live. Following Oda's demise, Dazai defected from the Mafia and went underground in order to heed Oda's final request for him to "be on the side that saves people". Admittedly, he reckoned that people change over time where potential surfaces, which apparently seems to apply to himself as well.

Upon joining the Agency, Dazai is usually called lazy, with Doppo Kunikida always scolding him for being unproductive and slacking off. Despite that, he has shown a sharp wit, deducing all the unlikely situations that led Atsushi Nakajima to believe he was being stalked by a tiger when he was the tiger in question. He has complete confidence no matter what type of situation he is dealing with, be it combat or simply bad situations he formulated in the first place.

In most occasions, Dazai is overly dramatic. He takes most of his actions as a joke, and, although they are very well-thought plans, he does not credit himself for most of what he has done. Dazai likes to tease anyone and everyone, especially if it means that he can get a laugh out of it. As a suicide maniac, he often attempts to commit suicide in comical manners, but he oftentimes fails or gives up on it when such methods are painful. Dazai, in particular, wishes to commit double suicide with a beautiful woman; though he admits that he "likes all types of women", he possibly prefers the type who would die with him if he asked to. Kunikida once wondered why Dazai is quite popular with women and called him a menace to women, a sentiment Chuuya Nakahara once used when he threatened to leak Dazai's address to every woman he ever made cry, which Dazai soon asked him not to do. Dazai also once had a run-in with a bomb threat instigated by a woman whom Dazai figured was obsessed with him.

While his suicidal tendencies are initially comedic, they reveal a truly dark deep hole that Dazai has. Even as a teenage boy, Dazai questioned whether there was any value in life. Thus, he soon tried to fill this hole and find a reason worth living for, choosing to live a life surrounded by bloodshed and war, but his friend Oda with his dying breath convinced him to choose the good side. He understood that even though good and evil mean little to Dazai, he may become a slightly better person if he were to choose well.

In the past, while he was still suicidal, it was shown to be far less comedic. He even described the death as a way to free himself from the oxidizing world, but, strangely enough, he could not die no matter how hard he tried. Additionally, he was extremely brutal and methodical, setting up traps to catch captives alive to torture them for information, and he would often beat his then apprentice Ryūnosuke Akutagawa for disobeying orders and to push him to the limits to improve his abilities.

While in the present he is more lighthearted and comical, he still retains some of his darker personality. He is still able and proficient at coming up with long-run strategies, though he doesn't inform his teammates what they are until the time is right. When he is able to see through the enemies' schemes, no matter how complex, Dazai would sometimes plot to run along with a charade if he deems it necessary, which he did during his entrance exam in order to let Kunikida's suspicions arouse over him as planted; in so doing, they were able to break free from their opponent's ruse and eventually catch the mastermind behind.

Dazai is also willing to use dirty means to achieve his goals, such as purposely deflating Ango Sakaguchi's car seat airbag when they crashed so Ango would get injured and force him to cooperate with Dazai for pardoning Kyōka in exchange for having his wounds healed.

Nonetheless, he does care for his teammates and watches out for them, especially Atsushi for whom he sees the greatest potential. Moreover, Dazai develops a sense of duty and utilizes his wit and intelligence to the Agency in their quest to help maintain Yokohama's peace and order. As part of his various plans and well-calculated strategies, he even devised for Atsushi and Akutagawa to collaborate at times to become a new generation of Twin Dark who could take on the brewing evil lurking within the city.

No Longer Human allows Dazai to nullify others' abilities on contact. It relies on skin contact and is always active. As such, he can nullify any ability even while restrained as soon as it touches him.