Here is a comprehensive manga synopsis for Koi Ichiya based on available information.

Set within the walled pleasure district of Edo-period Yoshiwara, Koi Ichiya follows the entangled lives of courtesans confined to their floating world of nightly illusion. Each night, love is both performed and betrayed in the locked cages of the red-light quarter. One courtesan swears revenge against a man who wronged her, clinging to hatred as her only power. Another slowly succumbs to a forbidden love even as she grows disillusioned with the men who visit her. Their stories weave together in a series of encounters where beautiful dreams mask a sordid trade, and the women must navigate desire, deception, and their own yearning for escape. The narrative arcs explore the tension between the romantic fantasy sold to patrons and the harsh reality of a life in service, culminating in a romance that is as much about the weight of the pleasure quarters as it is about the fleeting moments of genuine connection within them.