Kokushibo

Kokushibo is a major supporting antagonist of Demon Slayer: Kimetsu no Yaiba. He is a demon affiliated with the Twelve Kizuki, holding the highest position, Upper Rank One (の), and the right-hand man of Muzan Kibutsuji.

Nearly five centuries ago during the Sengoku Era, Kokushibo was once a human by the name of Michikatsu Tsugikuni, a former Demon Slayer and the older twin brother of Yoriichi Tsugikuni, the strongest Demon Slayer that ever existed.

Kokushibo is also the ancestor of Muichiro Tokito and Yuichiro Tokito and the one responsible for turning Zenitsu Agatsuma's senior, Kaigaku, into a demon and joining the Twelve Kizuki.

Appearance
Kokushibo is a very tall man with a lean muscular build along with pale skin and long, spiky black hair with red tips that he keeps in a ponytail. His most notable feature is the three sets of eyes on his face with yellow-orange irises and red sclera that have black straight lines diverging from each iris. His middle set of eyes has kanji of "Upper Rank" and "One" engraved in them while his other sets of eyes feature black pupils and a cracked pattern in the irises. Kokushibo also has red markings resembling flames on the top left side of his forehead and the bottom right of his chin. His appearance is described to be extremely dignified and majestic by Muichiro Tokito.

Kokushibo wears a purple-and-black bee-hive patterned nagagi kimono and black umanori-styled hakama pants tied with a white uwa-obi. 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.

As a human, Kokushibo's appearance was nearly identical to his demon form, with the exception of the number of eyes, his prominent eyebrows, and less pale skin. His eyes had dark purple irises and normal, white sclera as a human. As a child, he was usually seen wearing a white kimono as opposed to the purple-and-black patterned one he is seen wearing as an adult.

After being beheaded by Sanemi Shinazugawa and Gyomei Himejima, Kokushibo evolves into a more grotesque and monstrous form, with protruding fangs and mandibles, large white horns on the front and and back of his head, pointed nails, red outgrowths on his face, his pupils looking at different directions, shorter and messier hair, several thin tubes poking out of his body, and numerous black and red scorpion tail-like appendages haphazardly sprouting all across his entire body.

Personality
Kokushibo is reserved, silent, and aloof, maintaining an aura of unnerving tranquility and mystery that compliments 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, punctual, and he shows a great deal of respect to the hierarchy of the Twelve Kizuki, as seen at the Upper Rank gathering.Kokushibo is shown to be humble as well, and he did not hesitate to admit his failure or complain of any difficulty.

He displays a very strong sense of loyalty towards Muzan Kibutsuji, with most of his actions being done with the sole purpose of fulfilling Muzan's goals. Despite exhibiting outward reservation, dignity, and humility, there is a cold and unforgiving side to his personality; his words can be extremely harsh, especially when reprimanding individuals. His threats come off as nothing short of cruel and overwhelmingly serious, and he demands absolute obedience.

Kokushibo is shown to be genuinely delighted when the opponents he faced challenged him; such as helping dress Muichiro Tokito's amputated hand over his talented swordsmanship, praising Gyomei Himejima for his unparalleled human abilities and sparing Akaza because he enjoyed the challenge of battling him. However, due to this, he also felt irritation after he realized Akaza had died and he pities Gyomei for his impending death from unlocking his Demon Slayer Marks.

He possesses a complex relationship with his human past. He shows something of warmth towards his descendant, Muichiro, commending his skills and resolve, and being moved to convert Muichiro into a demon to spare his life. When their battle comes to an end Kokushibo displays his remorse at having struck down his descendants. At the same time, he refers to Muichiro and his abilities as the natural result of his "cells" being passed down.

In his duel against Gyomei, the demon's banter suggests a fear of death. When Gyomei's marks appear, Kokushibo pre-emptively bemoans the loss of a talented fighter and he urged him to become a demon to continue honing his skills. He seemed surprised when Gyomei vehemently rejected his offer and called his mentality pathetic.

It is revealed that as a human, Kokushibo 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, and this envy peaks when he discovers that Yoriichi was still alive and in old age, despite the curse of the Demon Slayer Marks supposedly killing him before he turned 25.

However, despite this immense jealousy, spite, and the outright hatred he harbors for Yoriichi, he still deeply cares for and loves his brother, as seen when he was touched by Yoriichi treasuring the handmade flute he had made for him as children; Kokushibo sheds genuine tears over his brother's death, and even goes as far as keeping the flute itself for the following centuries as a memento to his beloved and hated younger brother.

Likely a result of his inferiority complex and his immense desire for strength, Kokushibo fears the prospect of suffering defeat. So much so, he became increasingly more aggressive and agitated when being pushed further into a corner, causing him to become more desperate in his attacks and the use of his demon power. During his battle with the Hashira, he came to realize the steep price he had paid for the strength he desires so much; becoming an ugly monster far from his idealized dream of becoming the strongest samurai just like his brother, symbolizing how much his deep ambitions and resentment had warped him for the worst.

Moreover, his overinflated desire to surpass his brother is even shown in the form of his six eyes, which implies his desperation to attain the Transparent World in order to exceed his brother. In his last moments, he greatly laments and regrets his choices in his life and began to openly question himself if the path he walked was truly the right one. Kokushibo dies filled of regret, sorrow, and rage for not being able to accomplish anything that he had wanted, angrily asking his deceased brother why he was even born as he faded into ash.

Abilities
Overall Abilities: 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 near 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 in the organization.

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. During the Infinity Castle Arc, Kokushibo manages to effortlessly overwhelm the Mist Hashira, Muichiro Tokito, a prodigy who was previously shown to be capable of singlehandedly defeating Gyokko, Upper Rank Five, while injured. Later, Kokushibo easily slices off Muichiro's hand before he could react and is able to nonchalantly catch his sword mid-swing with his bare hand and proceeds to stab Muichiro with it.

Genya Shinazugawa, who played a major role in the defeat of Upper Rank Four, Hantengu, also stood no chance against the Upper Rank, being sliced into pieces with little resistance. Although the Wind Hashira, Sanemi Shinazugawa, was able to fair better than the former two due to his greater experience and capabilities, he was also quickly overpowered when Kokushibo decided to try harder, making deep cuts all over the Hashira's body that would've killed an average Hashira according to Kokushibo. Even when Gyomei Himejima arrived and momentarily stalled the battle by matching his strength and speed, Kokushibo quickly forced the Stone Hashira to use his Demon Slayer Mark. As further testament to his overwhelming power, Kokushibo could simultaneously hold back Sanemi and Gyomei, even when the two had their physical abilities increased by their Demon Slayer Mark.

Ultimately, it took the combined effort and abilities of Gyomei, Sanemi, Muichiro, and Genya, the former three who were marked, to even land a significant injury on him. Moreover, Gyomei and Muichiro also needed to see into the Transparent World. Despite that, the only way that the Demon Slayers could win was to immobilize him, which took the lives of Muichiro and Genya, the former sacrificing himself to leave Kokushibo in the open and the latter needing to utilize a new Blood Demon Art to restrain the Upper Rank. Even then, the Demon Slayers still met resistance due to Kokushibo's unnatural durability and needed to turn their blades bright red in order to behead him.

Despite all that, Kokushibo managed to regrow his head through sheer will, making him virtually invincible with the exception of the sun. How Kokushibo died can be left up to interpretation. It's equally likely that Kokushibo fell due to the realization of how ugly he had become in his pursuit of strength causing him to lose the will to fight or Kokushibo was completely unable to regenerate due to Muichiro's Bright Red Nichirin Sword hampering his regeneration when he was vulnerable after he regrew his head that caused his downfall. All in all, Kokushibo's defeat required the combined efforts of three powerful marked Hashira (two of which awakened the Transparent World) with Bright Red Blades, a Demon Slayer capable of using Blood Demon Arts, and even then, the battle was narrowly won and cost the Demon Slayers' two lives, a feat that truly displays the might of Upper Rank One.

Biological Absorption: Kokushibo possesses the ability to absorb human and demon bodies through physical contact. Although this trait has never been displayed, it is stated that Kokushibo would absorb the demons that challenged him and were defeated. It can likely be assumed that he uses this method as a faster alternative of consuming humans as well.

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: Similar to Yoriichi, Kokushibo not only has the ability to see into the Transparent World, but is also able to always use it. This allows him to see the muscles, blood flow, and joint movement of his opponents. He can accurately predict and anticipate the movements and attacks of his opponents with this ability. He was also able to identify that Muichiro was his descendant, immediately discern that Genya consumed demons to gain strength, as well as tell the strength of Muichiro, Sanemi, and Gyomei with one look, even being able to tell that the latter two's physical body and techniques are at their peak.

Extrasensory Perception: Kokushibo can detect the presence of others outside his normal range of perception, as shown when he dodged Genya's gunshots and appeared directly behind him despite Kokushibo looking at the opposite direction. Kokushibo also seems to be able to keep track of the locations of his peers around the Infinity Castle, evident as he no longer felt Akaza's presence when he died.

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 into possessing 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 and its own scabbard. Because of this, his katana can never be destroyed as he can regenerate it like he would with normal wounds. After undergoing a transformation after being decapitated, Kokushibo greatly morphed his body to adopt a more beastly and grotesque appearance, 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 as he quickly as healing his body, which was shown numerous times when the blade returns to its original shape when Gyomei or Sanemi damaged it with their attacks. Furthermore, he can freely manipulate the form of the blade, shown when he grew three additional blades from the original blade to increase its reach and further increase its size, turning it into a weapon similar to the Shichishito (Seven-Branched Sword). Later, Kokushibo also displayed the ability to grow and protrude dozens of blades from his own body, allowing him to perform a multitude of slashes from them without a swinging motion. From its activation alone, Kokushibo not only managed to blow away Sanemi and Gyomei, but slice apart Muichiro, Genya, the trees rooting him down, as well as numerous pillars in his surroundings.

Immense Durability: Due to having an extremely high concentration of Muzan's blood, Kokushibo possesses incredibly high durability. His neck is so resistant that a marked Sanemi barely made a cut despite swinging his sword with all his might. Furthermore, Gyomei's massive spiked iron ball similarly is ineffective in damaging his neck despite the Stone Hashira slamming his flail on Kokushibo's neck from above and the heat absorbed from the sun searing him. Even when a marked Sanemi slammed his katana down onto Gyomei's spiked iron ball, the Demon Slayers only successfully sliced off Kokushibo's head when both of their weapons turned bright red, which had to hamper his regeneration and burn his flesh.

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 Doma, regrowing his ear and right shoulder effortlessly. Later, after being decapitated by two marked Hashira, Kokushibo is able to regenerate his entire head and successfully conquered death by beheading after being decapitated by Nichirin Swords, a feat considered impossible for demons and only accomplished by two other demons: Akaza and the Demon King himself. However, while the speed at which he regrew his head was far faster than the former, his regeneration after being decapitated became unstable, causing him to take on a monstrous visage.

Immense Speed & Reflexes: Kokushibo possesses immense levels of speed far surpassing that of all his other Upper Rank brethren, as first shown when he slashed off Akaza's arm before he, or any of the other Upper Rank demons present, realized. He displays his phenomenal speeds on multiple occasions while fighting. Firstly, he is able to effortlessly outpace Muichiro's Mist Breathing techniques, moving so fast he appears to teleport. This caused Muichiro himself to state that Kokushibo's speed was in another dimension compared to his own, despite having his own speed being amplified from the Demon Slayer Mark. When Genya uses his shotgun to shoot the Upper Rank from a distance, Kokushibo manages to suddenly appear behind him before the bullets could reach, before slicing his arm off the moment he arrived. Afterwards, he slashes off his other arm and his torso so fast that his arms didn't even appear to move.

Later when his bout with Sanemi began, he could easily keep up with his techniques and movements despite the latter having to exert himself to the limit in order to stay alive. When Sanemi uses his brother's shotgun to shoot at the Upper Rank, Kokushibo is fast enough to block the bullets even when the shotgun is at point-blank range. After feeling the need to try harder, Kokushibo subdues the Wind Hashira with a single technique that was fast enough that he couldn't evade in time, delivering a multitude of cuts and slashes all across his body. Against Gyomei, the strongest Hashira of the current generation, Kokushibo is still more than capable of keeping up with his unorthodox attacks. Even after both Hashira became marked, an enraged Kokushibo could unleash sword attacks that even they couldn't fully react to and continuing to out-speed them with his techniques. His speed posed such a threat towards his opponents that Muichiro had to sacrifice a leg in order to stop the Upper Rank from moving so that Genya can fully immobilize him with his Blood Demon Art. After transforming, Kokushibo is able to move so fast, he appears as a blur to a marked Gyomei and Sanemi when they attempted to finish him off.

Immense Strength: As a transformed Demon Slayer who has gained the Demon Slayer Marks, on top of having the highest concentration of Muzan's blood, Kokushibo possesses immense physical strength. He is able to crack the ground just by stomping on Sanemi's sword, and is capable of wielding a gigantic sword much heavier than a regular katana and swinging it incessantly at immense speeds without rest or much effort. After transforming, Kokushibo was able to slice off Muichiro's arm with his bare hands akin to a blade.

Indomitable Will: Solely because of his goal to surpass his younger twin brother, Yoriichi Tsugikuni, Kokushibo possesses tremendous willpower and an indomitable spirit. Despite his decapitation at the hands of Gyomei and Sanemi's Bright Red Nichirin flail and sword, he forced his regeneration to evolve, and regrew his own head along with a myriad of enhancements, all because he didn't allow himself to die until he accomplished his goal.

Menacing Aura: Kokushibo possesses a menacing and overwhelming presence that temporarily made Muichiro Tokito, a Hashira who has faced and defeated countless demons and even an Upper Rank in the past, lose the will to fight and caused his body to tremble uncontrollably.

Monstrous Transformation: Later, after re-growing his head while battling Gyomei and Sanemi, Kokushibo undergoes a transformation that causes him to take on a more monstrous and grotesque form, with protruding fangs and mandibles, large white horns on the front and back of his head, pointed nails, red outgrowths on his face, his pupils looking at different directions, shorter and messier hair, several thin tubes poking out of his body, and numerous black and red scorpion tail-like appendages haphazardly sprouting all across his entire body. Kokushibo states that any attacks thrown at him in this state would be meaningless, and that the sun would be the only way to kill him.

Tactical Intellect: As a talented swordsman who has existed for nearly five centuries, Kokushibo has experienced countless battle situations and threats which he has learnt to overcome. This was displayed during his battle with three Hashira and Genya, where he was able to adapt to their special and unique fighting styles and tactics nigh instantaneously after witnessing it. After Muichiro unleashed his first attack against the Upper Rank, he was able to determine he was a user of Mist Breathing, a talented one at that. This was further accentuated through Kokushibo being able to take on Sanemi and Gyomei simultaneously despite both of them being marked and being users of different Breathing Styles, meaning he’d have to deal with 2 vastly different opponents at once, which he did so successfully, even overwhelming them multiple times.

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. Despite having his limbs and whole chunks of his body being repeatedly torn off and destroyed, he never once showed a sign of pain or agony. Even when his head was being crushed by Gyomei Himejima's spiked iron ball, he remained steadfast.

Fighting Style
Master Swordsman: Due to training and refining his swordsmanship skill for almost 500 years and getting a major boost to his physical capabilities, Kokushibo has become the most powerful and skilled swordsman in the modern era, and the second strongest swordsman in existence, behind his younger twin brother, Yoriichi Tsugikuni. As a Demon Slayer in the golden era, his swordsmanship was already outstanding as he learnt them from Yoriichi himself and later stated that their techniques were so refined and legendary that they have no hopes of it being passed down for future generations.

Kokushibo's skill in the blade allowed him to defeat Akaza, a prodigious hand-to-hand combatant and martial artist. With his exceptional sword wielding skill, he could singlehandedly take on Sanemi, Muichiro and Gyomei when they were marked as well as Genya when he assimilated his blood and gain a small portion of his power and had access to Blood Demon Arts. 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.

Breathing Style
Moon Breathing (の): 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. Kokushibo had continued to develop this Breathing Style and had created over a dozen techniques over the centuries he had lived.

Blood Demon Art
Crescent Moon Blades: Complementing his combat style: Moon Breathing, his 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 be created from his blood and can be either a bright yellow or a bright blue in color. These crescent moon blades are extremely chaotic, constantly changing in size, length and speed, making Kokushibo's attacks extremely unpredictable and unreadable as they have no set pattern. 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. Sanemi stated that if not for his years of experience in the field of demon hunting, he wouldn't have been able to defend himself from Kokushibo's attacks.

Kokushibo's Blood Demon Art seems to have a secondary ability which 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 red/orange crescent shape that carry 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.

Techniques

 * First Form: Dark Moon, Evening Palace (ノ　・の) - Kokushibo draws his sword and slashes swiftly in a singular horizontal motion in a crescent shape, creating numerous chaotic crescent blades. This technique is extremely reminiscent of Iaijutsu.


 * Second Form: Pearl Flower Moongazing (ノ　の) - Kokushibo performs several crescent-shaped slashes that defend him from incoming attacks, sending a barrage of crescent blades.


 * Third Form: Loathsome Moon, Chains (ノ　・り) - Kokushibo swings his sword rapidly in two gigantic crescent slashes, from which a storm of smaller crescents spread, causing huge destruction in a small area.


 * Fifth Form: Moon Spirit Calamitous Eddy (ノ) - Kokushibo makes multiple curved slashes layered over one another, creating a rising vortex of sword slashes and crescent moon blades.


 * Sixth Form: Perpetual Night, Lonely Moon - Incessant (ノ　・) - Kokushibo releases a wild barrage of crescent-shaped slashes several meters in front of him. This technique was powerful enough to overwhelm Sanemi Shinazugawa and so long-ranged that it slices up the surrounding pillars.


 * Seventh Form: Mirror of Misfortune, Moonlit (ノ　・え) - Kokushibo swings the gigantic version of his sword in a powerful frontal crescent-shaped slash that creates powerful multi-directional long-ranged slashes in the ground.


 * Eighth Form: Moon-Dragon Ringtail (ノ) - Kokushibo uses the gigantic version of his sword and creates a singular gigantic crescent-shaped slash that slowly decreases in size, creating dozens of crescent moon blades.


 * Ninth Form: Waning Moonswaths (ノ　り・) - Kokushibo creates a stream of long-ranged crescent-shaped vertical and horizontal slashes along with numerous crescent moon blades with the gigantic version of his sword.


 * Tenth Form: Drilling Slashes, Moon Through Bamboo Leaves (ノ　・) - Kokushibo creates a long-ranged triple-layered slash twister full of crescent moon blades with the gigantic version of his sword.


 * Fourteenth Form: Catastrophe, Tenman Crescent Moon (ノ　・) - Kokushibo uses the gigantic version of his sword and creates a chaotic vortex of powerful extremely long-ranged omni-directional slashes that destroys whatever is caught up within its attack radius.


 * Sixteenth Form: Moonbow, Half Moon (ノ　・れ) - Kokushibo creates a barrage of downward crescent slashes from an extremely long and wide range, resulting in a powerful six-fold slash crashing down on his opponents; the attack itself is powerful enough to create several miniature craters where the slashes have landed.

Equipment
Flesh Katana:As a former Demon Slayer and user of a Breathing Style, Kokushibo wields a demonically modified version of a Nichirin Sword. As suggested by its appearance, the weapon is created from his own flesh and blood, and due to his body's immense durability and hardness, its blade is as sharp, if not more so, as a regular Nichirin Sword. His sword is blood-red, with veins and his eyes all around the blade and even the hilt. However, it is unknown whether those eyes can be used to extend his vision. His katana's tsuba is circular with 4 slight indentations, a center with 3 eyes and several black veins and a golden border. He also carries a sword sheath at his waist that has the same fleshy appearance as his katana. According to the second databook, Kokushibo named his weapon Kyokokukamusari.

Trivia

 * Kokushibo's alias contains the On'yomi/reading of the kanji for "black" and the Kun'yomi/reading for "death" and "eye".
 * Kokushibo's human family name contains the Kun'yomi/reading of the kanji for "to inherit, succeed" and "country", while his first name contains the Nanori of the kanji for "sterness, severity" and the Kun'yomi reading for "to prevail, victory". His father was the one who named him, as he believed Michikatsu would be strong and successful.
 * Kokushibo has been challenged three times for his position. One of these battles involved Akaza. While Kokushibo would usually absorb the demon he defeated, he let Akaza live because he enjoyed the challenge.
 * Kokushibo is the first Demon Slayer to become a demon.
 * He became a demon in his early 20s and lived as such for an additional 460+ years.
 * Kokushibo once killed a leader of the Demon Slayer Corps. This caused the Corps to put extreme effort in hiding the residence of future leaders. This event was also the one that caused the Kakushi to be formed.
 * Kokushibo ranked 14th in the second popularity poll with 2938 votes.
 * The relationship between Yoriichi and Michikatsu parallels the mythology of the Shintō kami Amaterasu and Tsukuyomi, respectively. Amaterasu is the most sacred of Shintō deities, the sun goddess. Tsukuyomi, the moon god, is her former husband and brother. After Tsukuyomi killed Uke Mochi, another Shintō kami, Amaterasu refused to ever look upon him again, moving to another part of the sky and beginning the cycle of day and night. Like the deities, the siblings also feud and have chosen different paths (that of the Demon Slayer and the demon), developing their respective breathings of the sun and moon.
 * Kokushibo is considered to be a "business partner" by Muzan.

Quotes

 * (In regards to Akaza) "Akaza's presence is gone. He has fallen. Akaza... weren't you going to defeat me? A path had open for him to attain further heights... but he renounced it himself. How exceedingly weak."
 * (To himself) "The old and ugly creature that was once my little brother had pity for me. But... I wasn't angry. Even though 60 years ago, he had been such an eyesore. The voice calling me "brother" was terribly hoarse. My brother had never shown the slightest emotion... so at the sight of him shedding tears, something welled up in me for the first time since birth. I was confused... at my own unexpected unrest. But I must kill... this part of me from when I was human... This old man of brittle flesh past his prime... He was a Demon Slayer, and I must cleave anyone who turns a sword upon me. But his odd sentimentality... disappeared the next moment."
 * (In response to Yoriichi Tsugikuni's statement about future generations) "Yoriichi... when you smiled, I couldn't help it... but I always found it disturbing. And when we were talking about how there were no successors for the various breathing techniques you suddenly started viewing things with strange optimism and you smiled. In my conceit I believed that only our generation was special. I felt sick with disgust and irritation. What did you find so amusing? [...] What is so amusing about imaging such a future? Just thinking about losing makes me boil with anger."
 * (To himself) "The ugliness of not admitting defeat even though they took my head, chopped me up and crushed me. Living in disgrace. Have I lived hundreds of years for this? Was I so afraid of defeat that I became a monster? Did I want to be strong even if it meant eating people? Did I become this miserable creature because I didn't want to die? No. Yoriichi... I just wanted to be you."
 * (To himself) "I could never grab hold of anything. Anything at all. I abandoned my home. I abandoned my wife and children. I abandoned my humanity. I cut down my descendants and abandoned being a samurai. But even all that wasn't enough? You said that those who master their paths all reach the same place. But I never did. I could not see the same world that you did. Why could I not leave anything behind? Why could I not become someone known? Why are we so different? Why in the world was I ever born? Tell me... Yoriichi."

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