Kotohime monogatari, his first novel, was based on personal experiences in the brothel district, and it appeared in the literary magazine Chūōkōron in 1917.

In 1923, Muramatsu moved to China, where he lived in the Shanghai International Settlement in an apartment run by émigré Russians.

He also made the acquaintance of a number of young Chinese intellectuals, including Tian Han, Yu Dafu and Guo Moruo.

In his 1924 novel Mato (“Demon City”, 1924), he portrayed the dichotomy of Shanghai – a modern, beautiful, civilized façade, hiding a darker side populated by all manner of criminals and vice.

Some of the exaggerated fictional exploits created by Muramatsu were cited as “evidence” in Kawashima’s post-war trial, which led to her execution.