Setsuzan (雪山) was a gô (art name: 號) for Aikawa Hidenari (合川秀成), also known as Minwa (珉和), who died in 1821. Born in Kyoto, Setsuzan studied with Kishi Ganku (1749/56-1838, founder of the Kishi school of painting), but then turned to the ukiyo-e style for his paintings and book illustrations.
A yotaka (night-hawk: 夜鷹) is slang for a low-level or unlicensed prostitute, especially one who carries a straw mat to lie with her customers in the streets, alleyways, and canal embankments of the cities. Yotaka were among many themes found in fûzokuga (pictures of manners and customs: 風俗画), genre paintings depicting daily life and popular pastimes. Other subjects included views of commoners in cities or the countryside, festivals and ceremonies. Figures of many kinds were depicted, such as samurai, townsmen, children, artisans, merchants, peddlers, dancers, and street entertainers. Even stylish women and kabuki actors made their way into these genre scenes.
The poverty of the yotaka is revealed by her patchwork kimono and straw sandals. As she walks through the streets, she plucks her samisen (三味線, in Edo pronounced shamisen) to attract customers.
It is possible that this portrait was intended as a topic painting for a literati discussion group on classes in society. An unusual work by a rarely encountered artist.
References: Roberts, A Dictionary of Japanese Artists, p. 107.