~Kokushibo

Kokushibo is a tall man with a muscular build and a pale complexion. He possesses long, spiky black hair with red tips, that he keeps in a ponytail, along with two shoulder-length, flowing, wavy bangs on each side that reaches to his collarbone. His most notable feature is the six eyes on his face with yellow irises and red flesh sclera that have black straight lines diverging from each iris. His middle set of eyes has the kanji of "Upper Rank (上じょう弦げん, Jōgen?)" on engraved on his left eye, and daiji for "One (壱いち, Ichi?)" on his right, while his other sets of eyes feature black pupils and a cracked pattern in the irises. His top set of eyes replaced his eyebrows. Kokushibo also has red markings resembling flames for his Demon Slayer Mark on the top left side of his forehead that extended down to his left temple, and the bottom right of his cheek down to his right side of his neck. His appearance is described as profoundly majestic and dignified.

Kokushibo wears a purple-and-black hexagonal-patterned nagagi kimono and black umanori-styled hakama pants tied with a white uwa-obi, with pair of zōri with purple straps and white tabi socks. He carries a fleshy katana at his waist that, has eyes in the space between the tsuka ito wrapping of the handle of his sword. The tsuba and blade are shown to have eyes and veins. The scabbard is also fleshy in appearance.

Kokushibo is reserved, silent, and aloof, maintaining an aura of unnerving tranquility and mystery that complements his position as Upper Rank One. He rarely speaks; when he does, he talks in a slow and emphatic manner that gives more gravitas and authority to his words. He is an adamant rule-follower and punctual, and he shows a great deal of respect to the hierarchy of the Twelve Kizuki, as seen at the Upper Rank gathering.[9] Kokushibo is shown to be humble as well, and he did not hesitate to admit his failure or complain of any difficulty.

He demonstrates unwavering loyalty towards Muzan Kibutsuji as he carries out his actions solely to fulfill Muzan's objectives. Despite his outward display of reservation, dignity, and humility, there exists a cold and unforgiving side to his personality. When reprimanding individuals, his words can be harsh, bordering on cruelty. His threats are severe and demand absolute obedience. Having abandoned his humanity in the pursuit of strength, he shows a scornful view on humans. Throughout his life, Kokushibo was shown to be a man that greatly valued the concept of legacy. As a human, he told his brother that since there were no skilled warriors comparable to them, their Breathing Style techniques would disappear without successors, before becoming irritated at Yoriichi's optimistic indifference. When he realized that those that had awakened their Demon Slayer Mark died before reaching the age of 25 and grew worried that he was without a future, he accepted Muzan's offer to become a demon to further perfect his technique.

Kokushibo possesses a complex relationship with his human past. It is revealed that, as a human, Kokushibo, then Michikatsu, pitied Yoriichi during the period of time when he was mute, viewing him as a meek and callow boy dependent on his mother. He gifted him a flute to use when he needed his brother, and smiled at him despite being bruised from his father's beatings. However, he later harbored an immense sense of envy towards his younger twin brother for his natural talent and incredible abilities. These feelings of jealousy and contempt only became stronger upon seeing his brother become a peerless warrior of unmatched caliber among even the Demon Slayer Corps, with none of the Hashira coming close to his level of strength. This fostered a drive to become as strong or surpass his brother, a sentiment so strong that he abandoned his family to pursue becoming a Demon Slayer, and later, into a demon. His envy peaks when he discovers that Yoriichi is still alive and in old age, completely surpassing the curse of the Demon Slayer Marks that killed anyone that awakened them before they turned 25. Even centuries later, Yoriichi's immunity to the curse haunted Kokushibo.

As the highest-ranking member of the Twelve Kizuki, Kokushibo is an extraordinarily powerful demon, second only to the Demon King Muzan Kibutsuji himself. He has battled countless Demon Slayers and has amassed vast experience and knowledge over his nearly 500-year-long life. His abilities have been refined to the highest level, as he is not only a master of Total Concentration Breathing, but also a Marked individual who has gained access to the Transparent World, as well as the demon that possesses the highest concentration of Muzan's blood amongst the Upper Ranks.[12]

His overwhelming power is first displayed when he slashes off Upper Rank Three, Akaza's arm, before he could even react, and it is later stated by Doma that Akaza would never be able to surpass the both of them despite having improved his skills for 113 years prior to their meeting.

His abilities in a more specific term are:

Indomitable Will: Stemming solely from his goal to surpass his younger twin brother Yoriichi, Kokushibo possesses tremendous willpower and an indomitable spirit. Despite his decapitation at the hands of Gyomei and Sanemi, he forced his regeneration to evolve and regrew his own head, all because he didn't allow himself to die until he accomplished his goal.

Tactical Intellect: As a talented swordsman who has existed for nearly five centuries, Kokushibo has experienced countless battle situations and threats, which he has learned to overcome.

Biological Absorption: Kokushibo possesses the ability to absorb human and demon bodies through physical contact. Although this trait has never been displayed, it was stated that Kokushibo would absorb the demons that challenged him and were defeated. He presumably used this method as a faster alternative of consuming humans as well.

Flesh Manipulation: Like all demons, Kokushibo possesses the ability to manipulate his own flesh to a high degree. In terms of changing his body, he can alter his face to posses two more pairs of eyes while also elongating his forehead. Most notoriously, he uses this ability to create an extremely durable and sharp katana, complete with a tsuba, a tsuka, and its own scabbard. Because of this, his katana can never be destroyed, as he can regenerate it like he would with normal wounds. He also displayed the ability to grow and protrude dozens of blades from his body, allowing him to perform a multitude of slashes from them without a swinging motion. If being decapitated, Kokushibo would greatly morph his body to adopt a more beastly and grotesque appearance, with growing appendages, thin tubes, sharp mandibles, and horns.

Sword Manipulation: Due to his katana being made of his own living flesh, Kokushibo is able to easily regenerate parts of the blade should it be destroyed or damaged. Furthermore, he can freely manipulate the shape of the blade, as shown when he grew three additional blades from the original blade to increase its reach and size, turning it into a weapon similar to the Shichishito (Seven-Branched Sword)

Immense Regeneration: Kokushibo possesses one of the most powerful regenerative abilities in existence, second only to the Demon King, Muzan Kibutsuji. His regeneration speed is even faster than Akaza and Douma. After being decapitated by two Marked Hashira, Kokushibo is able to regenerate his entire head and successfully conquer death from a decapitation via Nichirin Swords, a feat considered impossible for demons and only accomplished by two other demons: Akaza and the Demon King himself.

Demon Slayer Mark: Kokushibo awakened his Mark when he trained under Yoriichi. The Demon Slayer Mark drastically improves the abilities of an individual, making them much stronger and faster than what they can achieve normally, though at the cost of being cursed to die at the age of 25. However, by turning into a demon and gaining immortality, Kokushibo is no longer bound by the curse.

Transparent World: Kokushibo has the ability to access the Transparent World, allowing him to see the muscles, blood flow, and joint movements of his opponents, as well as accurately predict and anticipate their movements and attacks.

Immense Speed & Reflexes: Kokushibo possesses immense levels of speed far surpassing that of the other Upper Ranks, as first shown when he slashed off Akaza's arm before he, or any of the other demons present, realized. He displays his phenomenal speed on multiple occasions while fighting.

Unlimited Stamina & Endurance: Like all demons, Kokushibo possesses infinite stamina and vitality, never tiring and always remaining in optimal physical and mental condition all the time, as well as being able to endure waves of onslaught as if it were nothing.

Extrasensory Perception: Kokushibo possesses honed sensory abilities that allow him to detect the presence of others outside his normal range of perception.

Menacing Aura: Kokushibo possesses a menacing and overwhelming presence that startled even Akaza, the holder of Upper Rank Three and an extremely vindictive and aggressive demon, into silence.

Master Swordsman: Due to training and refining his swordsmanship skills for almost 500 years and getting a major boost to his physical capabilities as a demon, Kokushibo has become one of the most powerful and skilled swordsmen to have ever lived. As a Demon Slayer in the Golden Age of Demon Slayers, his swordsmanship was already outstanding, as he learned many of his techniques from Yoriichi himself. According to himself, his techniques were so refined and legendary that they have no hopes of being passed down for future generations. Kokushibo's swordsmanship is further empowered with the development of his own Blood Demon Art, which greatly improves the lethality and power of his techniques, making every single one of his sword swings incredibly deadly.

Moon Breathing (月つきの呼こ吸きゅう, Tsuki no kokyū?): Kokushibo is the first demon that utilized Breathing Styles. His Breathing Style, in particular, is one of the most dangerous and powerful ones displayed thus far. Enhanced with his Blood Demon Art, he can create many chaotic crescent-moon blades when slashing that vary in length and size in crescent shaped sword attacks.[63] Kokushibo had continued to develop this Breathing Style and had created over a dozen techniques over the centuries he had lived.

Crescent Moon Blades: Complementing his Moon Breathing, Kokushibo's Blood Demon Art allows him to create and manipulate dozens of sharp blades shaped like traditional crescent moons from his flesh katana. They are implied to have been created from his blood and can be either a bright yellow or a bright blue in color. These crescent moon blades are innately chaotic, constantly changing in size, direction, and speed, making Kokushibo's attacks extremely unpredictable and unreadable as they have no set pattern at all. This Blood Demon Art greatly enhances the power of his techniques, making every single one of his sword swings extremely deadly and dangerous. He also seems to be capable of using his Blood Demon Art as long as his katana is unsheathed, allowing him to create crescent moon blades even without swinging his sword or unleashing a technique. The volatile nature of his Blood Demon Art makes it extremely challenging for Demon Slayers to circumvent. Kokushibo's Blood Demon Art seems to have a secondary ability that allows him to manipulate the shape and range of his sword slashes when unleashing his Moon Breathing techniques. His slashes usually create and are surrounded by a pink or orange crescent shape that carries his crescent moon blades. Kokushibo seems to be able to control said slashes to a certain extent, increasing their range and shape to attack his target in impossible ways under normal circumstances. When he distorted his katana into its branch-like appearance, his slashes turn into a light purple color. Kokushibo displayed the ability to exponentially increase the range of his sword slash with his Moon-Dragon Ringtail technique and shape his slashes into a circular drill-like shape with his Drilling Slashes, Moon Through Bamboo Leaves technique.

First Form: Dark Moon, Evening Palace (壱いちノ型かた　闇やみ月づき・宵よいの宮みや, Ichi no kata: Yamizuki - Yoi no Miya?) Kokushibo draws his katana and performs a singular horizontal slash following a crescent shape, creating numerous chaotic crescent blades along its path, before sheathing it back into his scabbard. This technique is extremely reminiscent of Iaijutsu.

Second Form: Pearl Flower Moongazing (弐にの型かた　珠しゅ華かノ弄ろう月げつ, Ni no kata: Shuka no Rōgetsu?) Kokushibo performs three crescent-shaped slashes while releasing a multitude of crescent moon blades along with them.

Third Form: Loathsome Moon, Chains (参さんノ型かた　厭えん忌き月づき・銷つがり, San no kata: Enkizuki - Tsugari?) Kokushibo performs two extremely broad crescent-shaped slashes directly in front of him, from which a storm of smaller crescent moon blades are released.

Fifth Form: Moon Spirit Calamitous Eddy (伍ごノ型かた 月げっ魄ぱく災さい渦か, Go no kata: Geppaku Saika?) Kokushibo creates multiple long and curved slashes layered over one another, essentially creating a vortex of crescent moon blades. As stated by Sanemi Shinazugawa, this technique was performed without Kokushibo swinging his katana.

Sixth Form: Perpetual Night, Lonely Moon - Incessant (陸ろくノ型かた　常とこ夜よ孤こ月げつ・無む間けん, Roku no kata: Tokoyo Kogetsu - Muken?)[74] - Kokushibo rapidly performs a multitude of curved slashes several meters in front of him that releases a wild barrage of crescent moon blades capable of slicing up the surroundings.

Seventh Form: Mirror of Misfortune, Moonlit (漆しちノ型かた　厄やっ鏡きょう・月づき映ばえ, Shichi no kata: Yakkyō - Zukibae?) Using his altered katana, Kokushibo performs a frontal crescent-shaped slash with couples of crescent moon blades, that unleashes numerous straight slashes with crescent moons interlaced, that expand outward through the ground.

Eighth Form: Moon-Dragon Ringtail (捌はちノ型かた　月げつ龍りゆう輪りん尾び, Hachi no kata: Getsuryū Rinbi?) - Using his altered katana, Kokushibo performs a extremely wide, long-ranged curved slash that leaves dozens of crescent moon blades along its path.

Ninth Form: Waning Moonswaths (玖くノ型かた　降くだり月づき・連れん面めん, Ku no kata: Kudarizuki - Renmen?) Using his altered katana, Kokushibo performs multiple downward curved slashes, all in close proximity, that leave numerous crescent moon blades along its path.

Tenth Form: Drilling Slashes, Moon Through Bamboo Leaves (拾じゅうノ型かた　穿せん面めん斬ざん・蘿ら月げつ, Jū no kata: Senmenzan - Ragetsu?) Using his altered katana, Kokushibo creates three rotating circular saw-like slashes with crescent moon blades following their path.

Fourteenth Form: Catastrophe, Tenman Crescent Moon (拾じゅう肆しノ型かた　兇きょう変へん・天てん満まん繊せん月げつ, Jū Shi no kata: Kyōhen - Tenman Sengetsu?) Using his altered katana, Kokushibo performs a multitude of curved circular slashes which expand outward in every direction that incrementally grow in size, essentially creating an omni-directional vortex of crescent moon blades that whirls around him. This technique is visually near-identical to Fifth Form: Moon Spirit Calamitous Eddy, albeit with much greater range.

Sixteenth Form: Moonbow, Half Moon (拾じゅう陸ろくノ型かた　月虹げっこう・片かた割われ月づき, Jū Roku no kata: Gekkō - Katawarezuki?) Using his altered katana, Kokushibo swings outward, sending six curved slashes crashing down in front of him with numerous crescent moon blades, powerful enough to leave craters in their wake.

Flesh Katana: As a former Demon Slayer and user of a Breathing Style, Kokushibo wields a warped version of a Nichirin katana. Created from his own flesh and blood, his body's immense durability and hardness allow it to be just as sharp, if not more so, as a normal Nichirin weapon made from Scarlet Crimson Iron Sand (猩しょう猩じょう緋ひ砂さ鐵てつ, Shōjōhi Satetsu?) and Scarlet Ore (猩しょう猩じょう緋ひ鑛こう石せき, Shōjōhi Kōseki?). Its blade is blood-red, with a veiny appearance, and numerous eyes cover the blade and the tsuka. However, it is unknown whether those eyes can be used to extend his vision. His katana's tsuba is circular with four slight indentations, a fleshy red center with three eyes and several black veins, and a purple border. The tsuka is wrapped with teal cords and capped with a purple kashira. He carries it inside a saya at his waist that shares a similar red fleshy appearance. Kokushibo named his weapon Kyokokukamusari (虛きょ哭こく神かむ去さり, Kyokokukamusari?, lit. "Hollow Cry of the Godless")