[1] A number of his most popular works, such as The Setting Sun (斜陽, Shayō) and No Longer Human (人間失格, Ningen Shikkaku), are considered modern classics.

Shūji Tsushima was born on June 19, 1909, the eighth surviving child of a wealthy landowner[3] and politician[1] in Kanagi, located at the northern tip of the Tōhoku Region, in Aomori Prefecture.

At the time of his birth, the huge, newly completed Tsushima mansion, where he spent his early years, was home to some thirty family members.

He also published a magazine called Saibō Bungei (Cell Literature) with his friends, and subsequently became a staff member of the college's newspaper.

[13] Dazai's success in writing was brought to a halt when his idol, the writer Ryūnosuke Akutagawa, committed suicide in 1927 at 35 years old.

Nine days after he was expelled from Tokyo Imperial University, Dazai attempted suicide by drowning off a beach in Kamakura with another woman, a 19-year-old bar hostess named Shimeko Tanabe [ja].

Dazai hardly participated in the strike, but in imitation of the proletarian literature in vogue at the time, he summarized the incident in a novel called Student Group and read it to Ueda.

On January 16 of the following year, the Special High Police arrested Ueda and nine other students of the Hiroko Institute of Social Studies, who were working as activists for Seigen Tanaka's Communist Party.

In college, Dazai met activist Eizo Kudo, and made a monthly financial contribution of ten yen to the Japanese Communist Party.

He was expelled from his family after his marriage to Hatsuyo Oyama in order to prevent any association of his illegal activities with his brother Bunji, who was a politician.

In December, Dazai signed and sealed a pledge at the Aomori Prosecutor's Office to completely withdraw from leftist activities.

He wrote at a feverish pace and used the pen name "Osamu Dazai" for the first time in a short story called "Ressha" ("列車", "Train"), published in 1933.

After fighting the addiction for a year, in October 1936 he was taken to a mental institution,[18] locked in a room and forced to quit cold turkey.

The year before last I was expelled from my family and, reduced to poverty overnight, was left to wander the streets, begging help for various quarters, barely managing to stay alive from one day to the next, and just when I'd begun to think I might be able to support myself with my writing, I came down with a serious illness.

The cold half pint of milk I drank each morning was the only thing that gave me a certain peculiar sense of the joy in life; my mental anguish and exhaustion were such that the oleanders blooming in one corner of the garden appeared to me merely flicking tongues of flame...In the 1930s and 1940s, Dazai wrote a number of novels and short stories that are autobiographical in nature.

Other stories written during this period include Dōke no hana (道化の花, "Flowers of Buffoonery", 1935), Gyakkō (逆行, "Losing Ground", 1935), Kyōgen no kami (狂言の神, "The God of Farce", 1936), an epistolary novel called Kyokō no Haru (虚構の春, False Spring, 1936) and thr stories in the collection Bannen (1936; Declining Years or The Final Years), which describe his sense of personal isolation and his debauchery.

Japan widened the Pacific War by attacking the United States in December 1941, but Dazai was excused from the draft because of his chronic chest problems, as he was diagnosed with tuberculosis.

Dazai's house was burned down twice in the American bombing of Tokyo, but his family escaped unscathed and gained a son, Masaki (正樹), who was born in 1944.

In 1946, Dazai published a controversial memoir, "Kuno no Nenkan" (Almanac of Pain), in which he describes the immediate aftermath of Japan's defeat and seeks to encapsulate how the Japanese felt at the time.

Dazai began writing his novel No Longer Human (人間失格 Ningen Shikkaku, 1948) at the hot-spring resort in Atami.

Keikichi Nakahata, a kimono merchant who frequented the young Tsushima family, was shown the scene of the suicide by a detective from Mitaka police station.