This article explores the source and the meaning of the eleven quatrains quoted by modern Japanese writer Dazai Osamu (1909-1948) in his last complete novel, Ningen shikkaku (No Longer Human, 1948). Although dubbed as “rubaiyat”, which would indicate that they are translations of classical Persian poet and mathematician Omar Khayyam (1048-1131), the poems do not seem to match any of the known English translations from his work. This article explores the origin of the Japanese quatrains in Dazai’s novel, as well as their possible relevance for his literary work overall.