His name is the same as that of the late author Osamu Dazai, and his personality was partially based on the main character from the television series The Mentalist.

Critical reception of his portrayal in the anime and manga has been mostly positive due to his interactions with his partners, Doppo Kunikida and Chuuya Nakahara, his personality, and his character traits.

Named after Japanese author Osamu Dazai (1909–1948), Kafka Asagiri created the fictional character to contrast with the protagonist, Atsushi Nakajima.

When conceptualizing his design, artist Sango Harukawa covered Dazai's body in bandages alongside other items meant to represent his obsession with suicide.

[4] When first reading the manga, anime director Yasuomi Umetsu was impressed by the relationship Dazai had with his students, Atsushi and Ryunosuke Akutagawa.

This gave the staff ideas for making the symbolic sequences in the opening and closing video scenes of the anime series where the three characters are featured.

[7] For the film Bungo Stray Dogs: Dead Apple, Asagiri suggested that Studio Bones change Dazai's hairstyle.

[10] Since being hired to be the English voice actor for Osamu Dazai, Kaiji Tang has looked forward to working on Bungo Stray Dogs, having previously watched the series.

[17] However, Dostoyevsky's men threaten the Agency again, and Dazai is imprisoned by Saigiku Jōno from the Hunting Dogs military government forces.

At the age of 20, he joined the Armed Detective Company on the recommendation of Chief Taneda of the Ministry of Internal Affairs' Special Ability Department and—as a newbie—was entrusted by Fukuzawa Yukichi to Doppo Kunikida.

Shortly afterwards, they were both assigned to work on the Serial Disappearance of Yokohama's Visitors Case, which Kunikida decided would be Dazai's entrance exam.

At the request of Ango Sakaguchi, the Armed Detective Agency investigates Tatsuhiko Shibusawa, a self-described "collector", tied to an incident involving multiple suicides.

[48] Anime News Network noted how dark this incarnation of Dazai is, as he does not appear to care for other people and instead ponders the idea of killing himself.

Nevertheless, the site liked his dynamic with Chuuya, with the Fandom Post echoing similar comments, especially during the Guild arc, as the duo can still fight together despite their distanced relationships.

[49][50] The relationship between the two former mafia allies was noted by Soochow University as one of the most famous shipped characters in China, which led to the nickname "DaChu" (太中).

Likewise, Dazai's character is heavily inspired by No Longer Human and its protagonist, Ōba Yōzō, with a few references to the historical author's life, personality, and preferences.

However, Dazai’s character has still made significant progress towards the fulfillment of Oda's wish and uses his inner darkness and past experiences to serve as a guiding light.

[55] Anime News Network felt that his role in the film, teaming up with Shibusawa and Fyodor, was too difficult to complete based on multiple stakes.

[56] Though Chuuya does not interact too much with Dazai in Dead Apple, their only encounters were noted in the book World Cinema On Demand: Global Film Cultures in the Era of Online Distribution to stand out for their homoerotic overtones among Chinese fans.

[37] The Fandom Post said that Dazai is a fun character, with Mamoru Miyano's "acting range helping his versatile characterization immensely.

[65] Rebecca Silverman referred to Dazai as her favorite character from 2016; despite first appearing in multiple suicide jokes, she felt he showed depths that portray him as a more mature person who influences Atsushi and Akutagawa to become stronger people.

[68] During an interview, Anime News Network regarded Dazai as one of the series' most popular characters, leading to far more appearances in other works besides the manga.

Asagiri was also surprised by this trend, and he considered that while there are several traits involving him besides Miyano's performance, he believes the reason for the character's popularity could be how interesting the core aspect behind his suicide attempts is, which attracts others, which he found unique based on his readings of the book No Longer Human written by the real Dazai.