Nakime

Set apart from most demons, Nakime is neither cruel nor bloodthirsty. She is detached and silent, rarely speaking and showing almost nothing beyond a willingness to carry out orders. Her loyalty to Muzan is absolute, and her flawless obedience earns one of the few compliments he ever gives anyone, though it reads more as satisfaction at owning a useful tool.

She keeps her distance from other demons and pays them little mind. During the meeting where the Lower Ranks are slaughtered, she watches without reaction. Later, facing two Hashira in combat, she stays calm and unmoving, confident that their attacks cannot touch her. Ironically, she was far more violent as a human, having murdered her husband in a rage.

In life, Nakime was a struggling, unknown biwa player tied to a husband who gambled away everything she earned. The night he pawned the only kimono she owned for performances, she killed him with a hammer. Forced onstage in tattered clothes with the shock of the killing still fresh, her trembling hands produced music so striking that the crowd demanded an encore. From then on she developed a grim habit of killing before each performance to recreate that tension. One day she chose Muzan as her victim, failed to kill him, and so impressed him with her searching talent that he turned her into a demon.

She climbed quickly through the ranks, eventually taking the Upper Rank Four seat left open after Hantengu's death.

Nakime's Blood Demon Art is the Infinity Castle itself, an alternate-dimension fortress she controls entirely by strumming her biwa. She can reshape its endless rooms at will, turning them into weapons by forming crushing pillars or luring foes to their deaths. By rooting her hair to the walls, she shifts and rearranges the structure as if it were her own body.

After becoming an Upper Rank, she gains the power to detach hundreds of eyeball familiars from herself, spying across vast distances and pinpointing the hidden locations of nearly the entire Demon Slayer Corps, including the long-concealed Ubuyashiki estate. She can teleport individuals into, out of, and around the castle, opening sliding tatami-door portals to transport allies on missions or to trap enemies. In the final confrontation, Yushiro seizes control of her vision and the castle through it, and Muzan kills her by crushing her skull to end the threat.