Kokushibo was a pale-skinned, tall man with long and spiky, black hair that he kept in a ponytail. He had three sets of eyes on his face with red sclera and yellow irises. His middle set of eyes featured the mark of Upper Moon One, and red markings resembling flames were seen on his face and neck.
Kokushibo wore a purple-and-black-patterned kimono and black hakama pants tied with a white cloth. He carried a sword at his waist that had eyes in the space between the tsuka wrapping of the handle of his sword. The guard and blade were also later revealed to have eyes and veins.
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 his notably less pale skin. His eyes had brown irises and normal, white sclera as a human.
After being beheaded by Sanemi Shinazugawa and Gyomei Himejima, Kokushibo evolved into a grotesque version of his Demon appearance, with protruding fangs, a pair of horns, and several sharp appendages from his body.
Kokushibo was often a reserved Demon, and with such little knowledge about the Upper Demon Moons, not much was originally known about him. He was an adamant rule-follower, punctual, and he showed a great deal of respect to the hierarchy of the Twelve Demon Moons - as seen at the Upper Moon Gathering. Kokushibo was portrayed to be humble as well, and he did not hesitate to admit his failure or complain of any difficulty. He displayed a 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 and humility, he was also rather cold; his words could be extremely harsh, especially when reprimanding individuals. His threats came off as nothing short of cruel and overwhelmingly serious, and he demanded absolute obedience.
He had a complex relationship with his human past. He showed something of warmth towards his descendant Muichiro Tokito, commending his skills and resolve, and moved to convert Muichiro into a Demon to spare his life. At the same time, he referred to Muichiro and his abilities as the natural result of his "cells" being passed down.
It was revealed that as a human, Kokushibo harbored an immense sense of jealousy towards his younger twin brother, Yoriichi Tsugikuni, for his natural talent and incredible abilities. These feelings of jealousy and contempt strengthened upon seeing his brother aged to an old man despite Yoriichi awakening his Demon Slayer Mark, which was to supposedly doom him to die at the age of 25. However, despite this immense jealousy, spite, and outright hatred he harbored for Yoriichi, he still deeply cared for and loved his brother, as seen when he was touched by Yoriichi treasuring the handmade flute he had made for him as children. Kokushibo shed genuine tears over his brother's death, and even went as far as keeping the flute itself for the following centuries as a memento to his beloved and hated younger brother.
In his duel against Gyomei Himejima, the Demon's banter suggested a fear of death. When Gyomei's marks appeared, Kokushibo preemptively bemoaned the loss of a talented fighter and urged him to become a Demon to continue honing his skills. He seemed genuinely surprised when Gyomei vehemently rejected his offer and called his mentality pathetic.
Likely a result of his inferiority complex and his immense desire for strength, Kokushibo feared 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 so much desired, becoming an ugly monster far away from his idealized dream of a strong samurai just like his brother, symbolizing how much his deep ambitions and resentment had warped him for the worst. Later upon his death, he greatly lamented and regretted his choices in his life and began to openly question himself if the path he walked was truly the right one.
Abilities and Powers
Kokushibo was an extremely powerful swordsman, considered to be the strongest of the Twelve Demon Moons and the second strongest Demon in the series, just behind Muzan Kibutsuji. As one of the oldest Demons in the series, he had battled numerous Demon Slayers and obtained vast experience and knowledge of combat. He was able to easily decipher the techniques and skills of at least two Hashira and overwhelm them in battle. As a Breath user, he possessed tremendous levels of strength and reflexes that were further enhanced by his Demon physiology.
These overall abilities and skills allowed Kokushibo to defeat two Hashira with minimal effort and then fight on par against Gyomei, who was considered to be the most powerful Demon Slayer in the Demon Slayer Corps. Even when Gyomei and Sanemi awakened their Demon Slayer Marks, which increased one's physical abilities way above their normal limit, he was still capable of holding his own against the both of them simultaneously.
When he started using his more of his power, Kokushibo managed to overwhelm both Gyomei and Sanemi, both of whom were boosted by their Demon Slayer Marks. As a testament to his might, it ultimately took a combo of attacks from Gyomei, Sanemi, and Muichiro to even land a significant injury on him. In the end, Kokushibo's loss was mostly a result of his sudden inability to regenerate and began crumbling due to realizing his mistake, rather than the skills of his opponents.
- Master Swordsman: Kokushibo was an extremely powerful and skilled swordsman. During his time as a human, he was one of the first Breath users.
- Immense Speed: Kokushibo possessed immense levels of speed, as shown when he outpaced Muichiro's Breath Techniques with great ease. Muichiro himself stated that Kokushibo's speed was in another dimension compared to the Hashira.
- Immense Durability: Kokushibo had displayed immense physical durability as seen when despite Gyomei using both his flail and axe to attack both ends of his neck, it still didn't budge. His neck was only severed thanks to both the combined efforts of both Gyomei and Sanemi putting all of their strength into forcing his neck to be sliced with Gyomei's axe.
- Demon Slayer Mark: A special Mark worn by certain "awakened" Demon Slayers that resembles Demon Marks. Its specific abilities are unknown, but what is know is that it drastically improves the abilities of the Demon Slayer, making them much stronger, faster and able to react quicker than what they can achieve normally, though at the cost of being cursed to die at the age of 25. As a Demon, not only was Kokushibo no longer bound by the curse, but the Mark's abilities were enhanced even further than when he was a human.
- See-Through World (
透き 通る 世 界Sukitōru Sekai?): Similar to Tanjiro, Kokushibo has obtained the ability to see the "see-through world" through the use of his three pairs of eyes. This grants him superhuman kinetic vision similar to Kanao Tsuyuri, allowing 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 the skill level of Muichiro, Sanemi, and Gyomei with one look, and see that Genya Shinazugawa consumed Demons to gain strength by looking into his cellular structures.
- Enhanced Regeneration: Kokushibo possessed incredible regeneration, able to regenerate his ear and right arm after getting cut by Gyomei with no effort. Later, upon being decapitated by two Hashira, Kokushibo was able to regenerate his entire head and successfully conquered death by beheading, a feat only accomplished by two other Demons: Akaza and Muzan. However, the process was slower than with Muzan and more unstable than Akaza, causing him to take on a monstrous form.
- Demonic Transformation: Later, upon regrowing his head while battling Gyomei and Sanemi, Kokushibo was able to transform himself into a demonic, monstrous form resembling a spider that presumably enhanced all of his abilities and powers.
- Telepathic Communication: Kokushibo is capable of being telepathically connected to Muzan Kibutsuji due to ingesting his blood, allowing him to have full conversations with the demon lord. As seen during his battle against the Pillars and Genya, Kokushibo was able to give a full report to Muzan, as well as receive new orders from him. This ability also allows Kokushibo to receive orders from across the country, and obtain the summons to gather at the Dimensional Infinity Fortress for meetings.
- Enhanced Breath Techniques: As a Demon, Kokushibo's Breathing Techniques has been enhanced to heights beyond even what Hashira can achieve. His former position was analogous to a Hashira prior to becoming a Demon, as well as his Demon Slayer Mark and being an Upper Moon, showing that his skill and efficiency with Full Focus Breathing is almost unparalleled, with only his naturally-gifted brother surpassing him.
- Blood Demon Art (
血 鬼 術Kekkijutsu?): Flesh Sword: Although the specific name of the Blood Demon Art is unknown, Kokushibo reveals that he had detached some of his own flesh and shaped it into the katana that he uses in battle. The blade possessed numerous eyes in the blade, handle, and guard, allowing him to have an increased range of vision while using it in battle. Since the blade was also created from his flesh, it could easily regenerate if destroyed or chipped. This ability is shown when the blade returns to its original shape in his battle with Gyomei. Kokushibo also displayed the ability to freely manipulate the form of the blade, growing three additional blades from the original blade to increase its reach and further increase its size. Later, Kokushibo also displayed the ability to grow and protrude multiple blades from his own body, allowing him to perform a multitude of slashes from them without a swinging motion. This attack was powerful enough to easily blow away two Hashira and destroy Genya's Blood Demon Art, as well as slice in half numerous columns in the room, from just its activation; the full usage of the Blood Demon Art being unknown.
Breath of the Moon (
- First Form: Dark Moon - Evening Palace (
壱ノ 型 闇 月・ 宵の 宮Ichi no kata: Yamizuki - Yoi no Miya?): Kokushibo 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.
- Third Form: Loathsome Moon - Chains (
参ノ 型 厭 忌 月・ 銷り San no kata: Enkizuki - Tsugari?): Kokushibo swings his sword rapidly in two crescent slashes, from which a storm of smaller crescents spread. This technique causes huge destruction in a small area.
- Fifth Form: Moon Spirit Calamitous Eddy (
伍ノ 型 月 魄 災 渦Go no kata: Geppaku Saika?): Kokushibo makes multiple curved slashes layered over one another resembling a rising vortex. Numerous chaotic blades originate from these slashes. Kokushibo performed this attack without swinging his blade.
- Sixth Form: Perpetual Night, Lonely Moon - Incessant (
陸ノ 型 常 夜 孤 月・ 無 間Roku no kata: Tokoyo Kogetsu - Muken?): Kokushibo releases a wild storm of slashes in multiple directions. This technique was powerful enough to not only slice up multiple Hashira around him but also overwhelm the Wind Hashira Sanemi Shinazugawa.
- Seventh Form: Mirror of Misfortune - Moonlit (
漆ノ 型 厄 鏡・ 月 映え Shichi no kata: Yakkyō - Zukibae?): Kokushibo swings his sword in a powerful frontal slash that then creates a multi-directional frontal assault, powerful enough to create several deep craters in the ground and push back at least two Hashira.
- Eighth Form: Moon-Dragon Ringtail (
捌ノ 型 月 龍 輪 尾Hachi no kata: Getsuryū Rinbi?): Kokushibo uses a direct frontal attack that creates a single gigantic slash.
- Ninth Form: Waning Moonswaths (
玖ノ 型 降り 月・ 連 面Ku no kata: Kudarizuki Renmen?): Kokushibo creates a seemingly endless stream of slashes capable of cutting down his intended target from long range.
- Tenth Form: Drilling Slashes - Moon Through Bamboo Leaves (
拾ノ 型 穿 面 斬・ 蘿 月Jū no kata: Senmenzan - Ragetsu?): Kokushibo creates a triple-layered slash twister capable of mowing down his targets into three clean pieces.
- Fourteenth Form: Catastrophe - Tenman Crescent Moon (
拾 肆ノ 型 兇 変・ 天 満 繊 月Jūshi no kata: Kyōhen - Sainan: Tengoku no mikadzuki?): Kokushibo swings his sword and creates a chaotic vortex of powerful omni-directional slashes that destroys whatever is caught up within its attack radius.
- Sixteenth Form: Moonbow - Half Moon (
拾 陸ノ 型 月虹・ 片 割れ 月Jūroku no kata: Gekkō - Katawarezuki?): Kokushibo brings down a downward slash that then produces a powerful sixfold slash crashing down on his opponents. The attack itself is powerful enough to create several miniature craters where the slashes have landed.
- Kokushibo is the older twin brother of the Breath of the Sun user who almost killed Muzan, Yoriichi Tsugikuni.
- Kokushibo is the first Demon Slayer to become a Demon.
- Kokushibo became a Demon in his early 20s and lived as such for additional 460+ years.
- The relationship between Yoriichi and Michikatsu parallels the mythology of the Shinto deities Amaterasu and Tsukuyomi, respectively. Amaterasu is the most sacred of Shinto deities, the sun goddess. Tsukuyomi, the moon god, is her former husband and brother. After Tsukuyomi killed Uke Mochi, another shinto deity, 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 breaths of the sun and moon.
- (In response to Muzan's reprimand) "I... have nothing... to say... Ubuyashiki... cleverly... hid... himself..."
- (To Akaza) "You... went too far..."
- (To Kaigaku) "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."
- (In response to Akaza's death) "You opened a path... to reach further heights... and you abandoned it... Very weak."
- (Last thought before death) "Have I lived hundred 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... I wanted to be like you..."