Kokushibo

Kokushibo is a member of the Twelve Demon Moons, holding the position of Upper Moon One. When he was a human he went by the name Michikatsu Tsugikuni.

Appearance
Kokushibo is a tall man with long black hair that he keeps in a ponytail. On his face, he has three sets of eyes with red eye whites and yellow irises. His middle set of eyes features the mark of Upper Moon one. on his face and neck are red markings resembling flames. He wears a patterned kimono with a black hakama. on his waist, he carries a sword which interestingly has eyes in the space between the tsuka wrapping of the handle of his sword. The guard and blade were also revealed to have eyes and veins.

Personality
Mainly, Kokushibo is reserved yet shrouded in mystery. If his actions at the meeting of the Upper Moons is anything to go by, however, he is a punctual, rule abiding individual who places high value in the hierarchy of the Twelve Demon Moons. He is also somewhat humble, as he did not hesitate to admit his failure or complain of any difficulties, instead acknowledging his opponent's strength.He has also displayed a strong sense of loyalty towards Muzan Kibutsuji,with a majority of his actions were simply done for the sole reason to be more useful in the latter's goals.

Among his reserved and humble nature lies a more cold side. That is to say, Kokushibo's words can come off as harsh, especially when reprimanding, and his threats can come off as nothing short of cruel and serious, almost overwhelmingly so.Later he reveals a more warmer side to his personality,having shown attachment to the family he left behind as a human and later showcased pride in the skills and abilities of his descendant,Muichiro Tokito and later tried to convince him to become a demon and even went as far as actually helping him by stopping his blood loss and later asked for forgiveness for cutting of his arm,although this behavior may simply due to the fact that he considers that Muichiro's skills were the result of being descendant from his "cells",showing a more narcissistic side to himself as well.

Human Life
As a Human Kokushibo's birth name was Tsugikuni Michikatsu,and somewhere along his life he somehow became a Demon Slayer,with him having remembering that he once trained and refined his sword skills with a former Breath of Wind user During the Sengoku Period and familiarized Himself with the Breath of Wind style,Later he had a child of his own who went on to continue his bloodline.

Demon Life
Somewhere Along the Line he was transformed into a Demon and Joined the Twelve Demon Moon and obtained the Rank of Upper Moon One,he being noted as one of the groups oldest members,Having fought numerous Demon slayers across the centuries.Three Hundred years ago he encountered a Demon Hunter who devoured demons to enhance his own and strength,having battled and defeated him by cutting his torso into two,killing him.

Red Light District Arc
Kokushibo was summoned to a meeting of the Upper Moons, arriving before any of his colleagues. He silently sat facing a wall, only speaking when his presence was acknowledged by the Biwa Demon, and revealing that Kibutsuji Muzan had arrived. Muzan revealed the death of Gyutaro, berating Kokushibo and his fellow Upper Moons for being unable to destroy the Ubuyashiki family and find the Blue Spider Lily. The prominent Upper Moon admitted he had nothing to say in his defense, as Kagaya Ubuyashiki had cleverly hidden himself.

After Akaza brutally destroyed Doma's head, Kokushibo covertly sliced off the former's hand, stating he had gone too far. He explained to Doma that he had not intervened for his benefit, but for the preservation of the hierarchy of the Upper Moon system. He then told Akaza to arrange for a blood battle if he wanted to take Doma's position, asking him if he understood what he was being told. Akaza acknowledged this fact, promising to kill the high-ranking Upper Moon, which Kokushibo wished him luck in before departing.

Dimensional Infinity Fortress Arc
Kokushibo is present in a flashback in Kaigaku's point of view, depicting the time just before he became a demon after Kokushibo defeats the Demon Slayer. He offers his own blood, as that will give Kaigaku more power that he desires if "that man" accepts him as their ally. And as he does, he threatens that if a drop of blood is spilled, the human will be beheaded.

Following Akaza's death, Kokushibo is seen alone. Murmuring how Akaza had abandoned his path to reach further heights and how he had failed to defeat Kokushibo, he reprimands how weak Akaza is. Simultaneously, he reaches for his katana, singlehandedly and instantly slicing the surrounding pillars to pieces in a single stroke.

Abilities and Powers
Kokushibou is an exceptionally powerful swordsman,being one of the oldest demons in the series,he has battled numerous Demon Slayers and has obtained a large pool of experience and knowledge of combat, having easily,deciphered the techniques and skills of at least Two Pillars and overwhelmed them in battle afterwards,and being a breath user he possess superhuman levels of strength and reflexes that where then further enhanced upon becoming a demon and gaining additional advantages thanks to his demon biology,He now possess over six pairs of eyes that grant him numerous levels of vision and superhuman kinetic vision similar to Kanao Tsuyuri,and has detached some of his cells into his own sword,giving himself additional eyes by attaching it to the blade.

As Upper moon 1,He is strongest Of all Twelve demon moons and second strongest demon in this series just behind Muzan Kibitsuji.

Breath of The Moon. Like Kaigaku, Kokushibo is a Demon with adept Demon Slayer Breath style,The Breath of the Moon being one of the most dangerous sword style displayed thus far,Sanemi noted that each and every slash and cut he makes using this breath style is surrounded by Chaotic crescent moon like blades that constantly change size and length,with the blades having no set form,thereby increasing the range of his already powerful attacks.
 * First Form: Dark Moon: Evening Shrine - Kokushibou draws his sword and slashes swiftly in a single motion, like with all Breath of the Moon techniques, numerous chaotic crescent shaped blades originate from the slash. This technique resembles Iaido.
 * Second Form:
 * Third Form:
 * Fourth Form
 * Fifth Form: Cursed Vortex of the Ghostly Moon - Kokushibou makes multiple curved slashes layered over one another resembling a rising vortex. Numerous chaotic blades originate from these slashes. Kokushibou performed this attack without swinging his blade.
 * Sixth Form: Solitary Moon in the Eternal Night: Avīci - Kokushibou releases a wild storm of slashes in multiple directions, this technique was powerful enough to not only slice up multiple pillars around him but also overwhelm the Wind Pillar Shinazugawa Sanemi.

Trivia

 * Kokushibo bears a striking resemblance to the first Breath of the Sun user.
 * Kokushibo is chronologically the first Demon Slayer to become a Demon.

Quotes

 * "I... have nothing... to say... Ubuyashiki... cleverly... hid... himself..." Chapter 98, page 15.
 * "You... went too far..." Chapter 99, page 3.
 * "Be thankful for the blood... You are not allowed to spill even a single drop on the ground... for if you do... your torso and head shall have a sorrowful parting." Chapter 145, page 5.
 * "You opened a path... to reach further heights... and you abandoned it... Very weak." Chapter 157, page 5.

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Кокушибо