Nakime

A female demon with long black hair covering her eyes, underneath which lies a large single eye. She is known as "Biwa Woman" or "Lady Biwa" among the Twelve Kizuki. Muzan favors Nakime, finding her useful.

She dislikes unnecessary conversation, responding briefly even when the Upper Moons One to Five gathered. Internally, she wished for a quick retreat.

Although originally an attendant separate from the Twelve Kizuki, she ascended to Upper Moon Four after Hantengu's death.

By playing the biwa, she freely manipulates the numerous rooms of the Infinite Castle, an alternate dimension. Despite lacking direct lethal power, her capability to control vast spaces far surpasses Kyougai. She can also interfere with demons and even summon Upper Moons to the Infinite Castle without their notice, teleporting demons and humans from room to room with her music. After becoming an Upper Moon, she acquired blood demon art of detection, using familiars with three tentacle legs attached to eyeballs to locate remotely.

As a human, she earned a living playing biwa, though impoverished due to her gambling-prone husband. After he sold her performance kimono to fund his habits, she killed him with a mallet in a fit of rage. Despite shaky hands and worn clothes from the murder, she received praise for her performance and began routinely killing people before playing. Targeting Muzan as her next victim, she was instead killed by him and turned into a demon.

During the Infinite Castle battle, she rooted herself in the walls by her hair, unable to move but maneuvered the rooms to separate the Demon Slayer Corps. Caught by Mitsuri and Obanai, she withstood their fierce attacks, buying time for Muzan's recovery. After Muzan's awakening, she continued altering the castle's structure to prevent the pillars from regrouping. However, during this, she was approached by Yushiro, who took over her brain, manipulating her vision and stealing control of the Infinite Castle. Upon learning this, Muzan abandoned Nakime, activating a self-destruction curse, causing her head to explode and resulting in her death. Consequently, the uncontrolled Infinite Castle collapsed, exposing it to the surface.