[1] His works like Geisha in Rivalry and A Strange Tale from East of the River are noted for their depictions of life of the demimonde in early 20th-century Tokyo.

[4] His father was an elite government official in the Home Ministry, who had studied as an exchange student in the United States[1] and also wrote and published Chinese poetry.

[6] From 1897 on, he started his regular visits to the Yoshiwara red-light district, accompanied by his friend and writer Seiichi Inoue (1878–1923).

[1] In 1910, Nagai started teaching as a professor of literature at Keio University and became the editor of the literary magazine Mita Bungaku.

[2] After a decade-long hiatus, he published the novellas During the Rains (1931), Flowers in the Shade (1934) and A Strange Tale from East of the River (1937), with the latter having repeatedly been cited as his major work.