Usugumo stands as the lead female character in "Oedo wa Nemurenai!". She carries the secret lineage of Tokugawa Yoshimune, the eighth Shogun of Japan, and a Christian courtesan, a heritage that places her life in constant peril from court assassins determined to erase the Shogun's secret. At fourteen years old, she holds the esteemed rank of top courtesan (tayuu) at Edo's Yoshiwara district Miura-ya brothel. This status grants her the right to refuse clients, a privilege she boldly exercises against the heir of the Kaga clan when he attempts to assault her. Usugumo characterizes herself as "strong against evil but weak about emotions," embodying the archetype of an Edokko (citizen of old Edo). Her defiance often manifests theatrically, such as a public outburst against the Kaga heir that spectators applaud as a performance.

She forms the vigilante thief group Kikugumi alongside the physician Aoto Touichirou (a shogunate agent assigned as her protector), the chivalrous thief Bentenkozou Kikunosuke, and her pet cat Kotetsu. The group steals from the wealthy to aid the impoverished and confronts adversaries employing advanced "Eleki" (electrical) weaponry. Within the manga's expanded narrative, Usugumo journeys to uncover her origins while navigating complex romantic entanglements. Multiple suitors develop affections for her, including Aoto and Kikunosuke, though her emotional attachments shift rapidly across the story due to unresolved longing for paternal acknowledgment. Her leadership within the Kikugumi evolves, positioning her at the forefront of their conflicts. The manga concludes with her romantically paired with Sangetsu, a former assassin who once targeted her—a resolution some narrative interpretations view as contentious. Later stages of the manga accelerate her character development amid convoluted plot twists, culminating in a finale some audiences criticized as rushed and inconclusive.

The OVA adaptation concludes with narrative conventions reminiscent of stage plays, implying ongoing adventures for the Kikugumi without a direct sequel.