Nakime

Nakime is a supporting antagonist in the Infinity Castle Arc of Demon Slayer: Kimetsu no Yaiba. She is the mysterious Biwa Demon who dwelled in the Infinity Castle. Initially, she was merely a Demon who served to summon other Demons into the castle on Muzan Kibutsuji's command, but, after Hantengu's death, she became the new Upper Rank Four (の) of the Twelve Kizuki.

Appearance
At the time of her debut, Nakime took the form of a pale woman with a grayish complexion, who had sharp, blue-stained nails and notably red lips which sharply contrasted the tone of her skin. She had shiny, waist-length hair of a dark brown color, which she wore falling down her back in slight waves that cut off sharply at the ends, with two chin-length strands left to frame her face and long bangs that obscured her large eye set in between them, swept to either side of her nose.

Nakime wore a plain black kimono with a white lining, secured with a striped pale brown-striped obi, white socks and no shoes. She was always seen holding a four-stringed wooden biwa with a large bachi pick.

Since becoming an Upper Rank, Nakime took to wearing her bangs as to not obscure her face, showing that she only possessed a single large, pink-colored eye with the kanji for "Four" etched onto its iris. The upper portion of her face was also revealed, and appeared to be a darker gray color than the rest of her skin with prominent veins surrounding her one eye.

Personality
Nakime was a mysterious yet cold biwa player who displayed little emotion. She didn't speak unless necessary and, when she did, she was always straightforward and blunt, making her responses as short as possible.

Rehabilitation Training Arc
Nakime makes her debut within the Infinity Castle playing her biwa, summoning the Lower Ranks for a meeting following Rui's death. She does not utter a word.

Entertainment District Arc
Nakime once again plays her biwa to summon the Upper Ranks to a meeting after Daki and Gyutaro's deaths.

When Akaza asks her where Muzan is, she replies straightforwardly that he has not yet arrived. She is also questioned as to where Upper Rank 1 is to which she replies (after Akaza's and Doma's bout) that he has always been there; he was the first to arrive.

At the end of the meeting, Nakime plays her biwa again to separate the Upper Ranks and bluntly refuses Doma's offer, cutting him off by sending him back to his temple.

Hashira Training Arc
Nakime, now the new Upper Rank 4 replacing Hantengu, is shown to be with Muzan. Using small eyeball familiars, she has been tracking down the Demon Slayers and determining their locations and hideout. Expressing her honor at Muzan's compliment for her rapid growth, she uses her technique to locate Kagaya Ubuyashiki.

Infinity Castle Arc
When the Demon Slayer Corps arrive at the Ubuyashiki mansion to try and stop Muzan, they are all transported into the Infinity Castle and separated from one another by Nakime.

Obanai Iguro and Mitsuri Kanroji are the first to encounter her, but find it extremely difficult to land blows on her due to her control over the environment.

After Kokushibo's death in Chapter 176, Nakime is the only remaining Upper Rank and the final member of the Twelve Kizuki.

Later, during the beginning of Tanjiro and Giyu's fight with Muzan, the latter reveals that Nakime has successfully "defeated" both Obanai and Mitsuri by crushing them both to death using the rooms of her castle. However, she is taken by surprise when the supposedly dead duo launch a surprise attack on her, still very much alive, and angrily asks Nakime what she's doing. Muzan is shocked upon learning that Yushiro has completely taken control over Nakime's vision, and with it, the Infinity Castle, which he begins to use against the Demon lord as revenge for his killing of Tamayo.

Muzan immediately begins countering Yushiro, using his own mental powers in order to take back his final Upper Rank, which kicks off a fierce battle of wills between the two Demons. This mental fight causes the castle to completely spiral out of control as both wrestle for dominance, and, just as Muzan appears to have taken the upper hand, Obanai and Giyu launch an attack on the Demon lord. He has no choice but to counter, which causes his hold on Nakime to slip as he tries to defend himself and ward the Hashiras off with his own attacks.

Soon realizing that he can't take back Nakime and fight the Demon Slayers at the same time, Muzan uses his powers to kill his final Upper Rank by crushing her head, which prevents Yushiro from using the castle against him and allows him to fully focus on killing the remaining Hashiras and Tanjiro. As Nakime doesn't immediately disintegrate, Yushiro manages to use her body to push the castle above ground in an attempt to protect the Demon Slayers.

Abilities
Overall Abilities: As the new holder of the Upper Rank 4 title, Nakime possessed a tremendous amount of strength. She was capable of using her abilities to hold her own against Obanai and Mitsuri, two incredibly strong Hashira, simultaneously, without either of them being able to so much as scratch her.

Supernatural Abilities
Eye Detachment: Later, upon obtaining the rank of Upper Rank 4 and presumably receiving more blood from Muzan, she displayed the new ability to create and detach several eyeballs from her body. This allowed her to spy on others from a long range. With this new ability, she was able to successfully find and locate the positions of nearly all members of the Demon Slayer Corps as well as the hidden mansion of Kagaya Ubuyashiki, who had gone to extreme lengths to hide its location from even the highest-ranking members of the Demon Slayer Corps.

Blood Demon Art
Castle Manipulation: Nakime possesses the ability to manipulate and create a seemingly infinite castle just by playing her biwa. She can create and shape rooms, like an open room filled with giant pillars where the fight against Kokushibo took place; a small garden where the fight against Doma took place; a corridor leading to several other rooms where the fight against Akaza took place. Nakime can also use this ability for offensive purposes by shaping rooms into gigantic pillars and ramming it into her enemies to crush them. By binding and rooting her hair to a nearby wall inside the castle, she could control the castle's positioning as she liked: shifting and changing the positioning of various rooms and walls as if they were her own limbs. However, doing so rendered her immobile.
 * Portal Creation: Nakime can also create portals in the form of doors. She can use her portals for offensive and defensive purposes as well, displayed when she created a portal to negate Mitsuri Kanroji's attack. One of her main duties was to act as a mode of transport for the Upper Moons when they are sent on missions and presumably assist Muzan in moving around the country undetected.
 * Spatial Manipulation: Nakime can manipulate space in her castle to a certain degree. She can use this ability to teleport all those present in her castle to any other location or even outside without having to create portals.

Miscellaneous Abilities
Talented Biwa Player: Nakime was an expert at playing the Biwa, garnering attention from others when she performed while she was still a human.

Trivia

 * Nakime has many similarities to the former Lower Rank 6, Kyogai. They both use Blood Demon Arts that allow them to freely manipulate a specific structure at will, have a musical instrument to use their individual techniques, and have been given their epithets based on these instruments.
 * She was one of Muzan's favorite Upper Ranks, since he believes her ability is useful.
 * Nakime's name was mistakenly translated as "Nasume" in the official English release of Volume 12.

Quotes

 * (To Doma) "I refuse."
 * (In response to Muzan Kibutsuji's praise) "I am very honored."

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Накиме Nakime