Dazai, Osamu (ōsäˈmō däˈzĪ) [key], pseudonym of Shuji Tsushima shōˈjē tsōˈshĭmä, 1909–48, Japanese novelist. Considered one of the foremost fiction writers of 20th-century Japan, Dazai was noted for his ironic and gloomy wit, his obsession with suicide, and his brilliant fantasy. In the 1930s and 40s he wrote a number of subtle novels and short stories that are frequently autobiographical in nature. His first novel, Gyofukuki (1933), is a grim fantasy involving suicide. His stories, published as Bannen [declining years] (1936) describe his sense of personal isolation and his debauchery. In Otogi Zoshi (1945) he retold a number of old Japanese fairy tales with vividness and a trenchant wit. The decline of the Japanese nobility after World War II was his theme in The Setting Sun (1947, tr. 1956). He depicted a dissolute life in postwar Tokyo in Bion no Tsuma (1947). His No Longer Human (1948, tr. 1958) was a rephrasing of much autobiographical matter. Dazai committed suicide while working on a novel entitled Good-bye.