Oyuki appears in the Lone Wolf and Cub saga as a tattooed female assassin, introduced as the renegade member of a daimyo's personal bodyguard detail who has turned against her former masters and is killing every fighter sent up against her. Her roots lie among a settlement of street performers and traveling entertainers, where her father serves as the elder of the troupe. He opposes her violent ways and ultimately cooperates with those who come hunting her. Her path is forged by a deep trauma: her former martial arts instructor raped her, and that act of betrayal set her on a destructive vendetta against men.

In personality, Oyuki is hardened, fearless, and consumed by a need for retribution. She fights with brutal efficiency and shows no mercy to the samurai dispatched to kill her, going so far as to cut off their topknots after defeating them, a deliberate gesture meant to bring dishonor to the dead and shame to their families. Despite her cruelty, she is not without a personal code. She endured the painful process of receiving elaborate tattoos across her body without a single cry, and by the time she is confronted by her old instructor she has broken free of his hold over her, including his hypnotic gaze. When he appears before her with his flaming sword and blazing eyes, she no longer falls under his sway, and the shocking sight of her tattoos distracts him long enough for her to kill him.

Her most notable abilities are her skill with the short blade and her unusual fighting method. While battling, she strips to the waist to reveal the artwork inked into her skin: a kintaro figure on her front grasping her left breast and the portrait of a mountain witch covering her back. The tattoos serve as both a psychological weapon and a distraction that unsettles her opponents. Her backstory is uncovered by Ogami Ittō, who is hired to kill her; through the tattoo artist who decorated her and the elder of the performer settlement, he learns of her past as a woman who once showed great fortitude and was considered a fine person before her tragedy.

In the story, Oyuki functions as a mirror of the themes of vengeance and honor that run through the series. She is an assassin whose quest for justice has curdled into a bloody rampage, and her final encounter with Ittō drives this home. After he witnesses her kill both the vassals sent against her and her former tormentor, the two duel, and Ittō makes quick work of her. She dies an honorable death, remarking that she was allowed to pass without having to disrobe once more. In that moment, her development comes full circle: from a victim turned relentless avenger, she becomes a figure who accepts her end with composure and dignity, reclaiming a measure of the honor her vengeance had stripped away.