Kokushibou

"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."

- Kokushibou to Kaigaku

"You opened a path... to reach further heights... and you abandoned it... Very weak."

- Kokushibou in response to Akaza's demise

Kokushibo is the secondary antagonist of Demon Slayer: Kimetsu no Yaiba. He is the strongest member of the Twelve Demon Moons, holding the position of Upper Moon One and the right-hand of Muzan Kibutsuji, and the ancestor of Muichiro Tokito (the Mist Pillar) and Yuichiro Tokito.

Before becoming a demon, he was a Demon Slayer named Michikatsu Tsugikuni and was speculated to be one of the first Breath Users. Kokushibo bears a striking resemblance to the first Breath of the Sun user.

In Chapter 174 it is eventually revealed that Kokushibo is the elder twin brother of Yoriichi Tsugikuni, the first Breath of the Sun user.

Physical Apperance
Kokushibo's physical apperance shares a striking similarity with Yorichii, his own brother. He is a tall man with long black hair that he keeps in a ponytail. Before his turning point, he shows no difference to normal human. However, after becoming a demon, his apperance significantly changed, with his face covered in three sets of yellow eyes with red eye whites, with six eyes in all.

It was implied that his power was so strong that the physical distortion on his visage even extended onto his katana, with its guard and blade also covered in eyes and veins. His outfit was consisted of a patterned kimono with black hakama on his waist, where he carried his sword.

Personality
Kokushibou is a mysterious but composed, grim, serious and somewhat honorable individual who never plays around. When a fight starts and his sword is drawn, he aims to bring his opponent down and break them completely. The most he'll allow is for a defeated foe to become a demon themselves. He is also the most loyal enforcer of Muzan's Upper Moon system, willing to punish Azaka for breaking the rule and attack Douma, though he does suggest Azaka to fight Douma and earn his place if the latter really disgusts him.

Despite being a demon, Kokushibou relies more on his swordsmanship and Breath of the Moon techniques rather than using the supernatural Demon Blood Arts. His past also revealed himself to be a distraught and broken man who was sad over his shortened lifespan and with a great fear of death, as well as a grudge born out of jealousy towards his younger brother to the point of making a notion to kill him.

In spite of his cruelty, Muichirou is also an honorable person who gives respect to opponents he considered worthy. After discovering that Muichirou is his direct descendant and analyzing his fighting skills, he gives him great respect and even offers him to become a demon and join Muzan's army if Muzan allows it.

However, he gives the greatest respect to Gyomei Himejima, who he claims is the strongest Pillar he has fought in over 300 years and tries multiple times to get him to become a Demon so that he can preserve his Techniques, since the Demon Slayer Mark will kill him by the end of the night.

Human Life
Originally a human born in the Sengoku Period, Kokushibou's birth name was Tsugikuni Michikatsu, and he is the elder twin brother of Yoriichi Tsugikuni, the original Breath of the Sun user and Muzan's arch-enemy. He was also the ancestor of Muchiro, the current Mist Pillar, thanks to fathering a child before his demonic transformation, with the said child continuing his bloodline.

After years of training, Tsugikuni developed his own Demon Slayer mark, wielder with the said mark was stated that their lifespan was shortened so serious that they can only live to 25 years old. Possibly out of fear of his own death, Tsugikuni joined force with Muzan Kibutsuji and became a demon so that he could live forever. Because he was originally a Breath user, it took him three days to suppress his Breath techniques and fully transform into a demon. Renaming himself Kokushibo, he started a hunt towards his elder brother for pure vengeance.

Demon Life & Fractricide
400 years before the story, Tsugikuni/Kokushibo hunted down his brother for decades, and discovered that while Yoriichi had developed the mark as well, he managed to live pass 25. When Kokushibou find him, Yoriichi was already an old man in his eighties.

Surprised that his brother managed to live a long age even with the mark, Kokushibo believed that he had never met his brother for sixty years. He kept questioning why Yoriichi was still alive, and Yoriichi tearfully replied that his brother's choice was such a pity. Kokushibo saw his brother's tears and was deeply guilty about his jealousy and choice. However, knowing the brothers will destinied to slay each other, Kokushibo still determined to kill Yoriichi, knowing he was too senile to live any longer.

Yoriichi then got ready to fight before landing a slash on Kokushibo's shoulder, with the latter feeling pressed by an unseen force. Shocked, Kokushibou realized that his brother's strength never faded in spite of his age and frail state. Jealous over it, Kokushibou was filled with hatred and decided to finish his brother once and for all.

Feeling that the next slash will be a fatal attack, Kokushibo turned around and prepared to land his attack before Yoriichi could behead him, realizing that his brother was the very same warrior that was so strong that he even cornered Muzan himself once. Fearing the failure, Kokushibo decided to finish the battle off. However, once he turned around, Kokuboshi discovered that his brother stood still. Immediately, Kokuboshi came to the conclusion that his brother was dead.

Kaigaku's Surrender
Years before the story, Kokushibo had a confrontation with Kaigaku, who was overpowered and defeated, before surrendering to Kokushibo due to his power. Seeing Kaigaku begging for mercy and his service, Kokushibo then offered his own blood and the power given by Muzan. He claimed that Kaigaku will become his companion if he accepted the blood and then if Muzan is willing to accept him as an ally. As Kaigaku complied, Kokushibou threatened that if a drop of blood is spilled, the human will be beheaded.

With great care, Kaigaku accepted Muzan's blood from Kokushibou and became a demon, trying to fulfill his desire to become stronger. After Kaigaku becoming a demon, his master committed suicide out of guilt and shame.

Red Light District Arc
After the deaths of Daki and Gyuutaro, Kokushibou and other Upper Moons were summoned by Muzan Kibutsuji to a the Dimensional Infinute City meeting, arriving before all of his colleagues. He sat silently to the wall until he was awared that Muzan arrived. Muzan berated Kokushibou and his fellow Upper Moons for their constant failure, and Kokushibo admitted to his own failure and believed that Kagaya Ubuyashiki had cleverly hidden himself.

After the meeting, Douma sarcastically mocked Azaka, twice, causing the latter to destroy Douma's head in half, though it soon regenerated. As a punishment to Azaka's behavior, an irritated Kokushibou covertly sliced off the former's hand due to his violation of the hierarchy of the Upper Moon system, claiming that Akaza had gone too far. He explained to Douma that he had interfered for enforcing thenot intervened for the latter's benefit, but for the preservation of the hierarchy.

After things were settled down, Kokushibou then stated that if Akaza really despises Douma, he should take his place in a bloody fight. Agreeing Kokushibou's opinion, Akaza then challenged the high-ranking Upper Moon, with Kokushibo wished him good luck before leaving.

Kokushibou VS. Muchiro
Following Akaza's death, Kokushibou is seen alone. Murmuring how Akaza had abandoned his path to reach further heights and how he had failed to defeat him, Kukushibou reprimanded how weak Akaza was to take his own life, before cutting the stone pillars around him with his katana.

Some time later, Muichiro Tokito is transported to the same room as Kokushibo, who deduded that the latter was his descendant, from a line that continued by his own child he left behind when becoming demonic. He also deduced that his human surname of Tsugikuni has died out over the generations, leaving his own name being forgotten.

After witnessing Muichiro's Demon Slayer Mark and Breath of Mist style, Kokushibo was impressed and praised Muichiro for his swordsmanship at such a young age, claiming it must be out of his own family's bloodline, but Muichiro dismissed it. They began to fight against each other, but Kokushibo quickly overpowered his descendant and cut off one of his arms. Nevertheless, Muichiro quickly tightens his arm to stop the bleeding. Kokushibo became even more impressed and pinned Muichiro against a pillar effortlessly. Kokushibo then offered a chance to Muichiro to serve Muzan as a demon so that he can continue to live.

Fighting Sanemi Brothers
However, his discussion is interrupted by Genya Samemi shooting his Nichirin Gun. Kokushibo easily avoids the gunshot, appearing behind Genya and then proceeding to cut off both his arms and his torso in half, recognizing him to be the one who is eating demons. However, he realizes that Genya was unlike the other imitation demon from 300 years ago and that the way to kill him was to behead him like how the regular demons were killed.

Fortunately, Genya was saved by his brother, Hashira Sanemi (the Wind Pillar), before Kokushibou could stand a chance. Genya apologized for everything he had done to Sanemi, and the brothers finally reconciled with each other. In a sad face, Kokushibo witnessed this and had a nostalgic feeling of him fighting alongside his late brother, lamenting his own past before beginning to duel Sanemi.

Very briefly, Kokushibo was slightly taken aback at the skill of Sanemi. However, he retained his composure and fought with expeirence of fighting a past Wind Pillar, before having a serious cut on Sanemi, stating that moving would lead to his entails to spill out. Sanemi proceeded to use his rare blood to lure demons, in the same way he once tried to test Nezuko and prove her threat (but failed since Nezuko refused to attack him).

Though briefly mesmerized by Sanemi's rare blood, Kokushibou instantly regained his composure and overpowered Sanemi. After some struggling, Kokushibo stated it was pleasure to fight such a strong Pillar and decided to deal a significant blow.

One Against Four
However, he was soon interrupted by Gyomei, the Stone Pillar, who rescued Sanemi in time. Kokushibo is now unable to retain himself, openly stating that he hadn't meet a great swordsman like Gyomei for 300 years. Following an intense back and forth battle, Gyomei used his Demon Slaying Mark on himself to fight Kokushibou, though stating once it was his trump card he meant to save for Muzan. Because Gyomei was already 27 years old, his current state shortened his lifespan into just one night, and he will be dead by dawn.

Understanding his situation because of bearing the same kind of mark, Kokushibo offered Gyomei an opportunity to become demonic so he can survive and continue to hone his craft the same way he has. Gyomei outright rejected the offer and stated that there was still a mark bearer who lived passed 25 and was still alive. Possibly ringing a bell of his very own brother, Kokushibo panicked for a little bit but resumed his fight.

Meanwhile, Sanemi seized the chance and continued to stitch his wound, eventually rejoining the fray as the two now face Kokushibo in a two on one battle. The three of them continue their battle until suddenly, Kokushibou evolved his own katana, turning it towhat appears to be an elongated sword with three blades extending out the sides (tow on one side and one on the other). Cutting the Sanemi Brothers by it, Kokushibo decided to go serious against his current opponents.

During the meantime, Muichiro manages to free himself from the literal pillar and helped Genya by reattaching his body and feeding him a piece of Kokushibo's hair. Absorbing the power of Kokushibou, Genya then felt power he's never felt before, but more importantly appears to directly hear Muzan's words meant for Kokushibou, with Muzan asking how many Pillars have him defetaed, indicating that Muzan is likely still incapacitated by the initial explosion and the Blood Demon Art Tamayo performed on him.

As Gyomei and others stalled Kokushibou back, Genya recalled his discussion with Tanjiro about how he defeated the previous duo of Upper Moon Six. Knowing he was too weak to get attention from Kokushibou, Genya swallowed a piece of Kokushibou's broken blade and empowered himself further.

Turn of the Table
Meanwhile, Kokushibou discovered that Gyomei managed to predict his own action and see through his weakness, even though he was blind, since he also possessed the ability of See-Through World. As a result, he used the Sixteenth Style of the Breath of the Moon against the Pillars. Muichiro managed to get close to Kokushibou and cut off the demonic swordsman's right arm, at the cost of a leg.

Struggling against Kokushibou, Muichiro shouted at Gyomei to take action right now. Kokushibou then discovered Genya, now barely human in appearance, aimed the now mutated Nichirin Gun at him. Heeding Muichiro's encouragement, Gyomei fired bullets at Kokushibou, who tried to deflect it with his katana. However, the bullets changed their track and hit Kokushibou's arm, much to his dismay.

Kokushibou then laid his eyes on Gyomei and discovered that his gun was covered in demon eyes, just like the own katana of Kokushibou, making him realized that Gyomei absorbed his own power. Before Kokushibou could react, Gyomei used the Blood Demon Art he gained from his mutation to turn the bullets into branches, trapping Kokushibou in a tree. Seizing the chance, the three Pillars immediately marched on and prepared to give him one last strike.

Struck by horror and paralyzed by the tense feeling, Kokushibou recalled his brother's last moment four centuries ago, knowing that the latter was the very first man who drove him into such fear.

Quotes
"Wonderful. The perfect physical form developed to the utmost. How long has it been since I've set my eyes on such a great swordsman, perhaps 300 years?"

- Kokushibou complimenting Gyomei

"You merely shredded my kimono, not even enough to kill an infant. Once I dispatch you two, the rest will proceed easily."

- Kokushibo as he revealed his evolved blade

"You came Demon Slayer. For some reason, hmm? You, you seem familiar."

- Kokushibou to Muchiro

Trivia

 * Kokushibo is chronologically the first Demon Slayer to become a Demon.
 * Kukushibo's name means "".
 * A panel in Chapter 128 forshadows that Kokushibo and Yoriichi are siblings, largely because of their shared physical feature. It was foreshadowed even further when Kokushibo mentioned fighting with his brother once when he witnessed Pillars sticking together against him. Chapter 174 comfrimed his relationship.
 * He was a human from, at the very least, 300 years prior the current setting and with that he speaks in extremely antiquated Japanese, how much of that is translated into English varies within fan translation efforts, the official Viz Media translation puts a little more effort in adapting Kokushibou’s manner of speaking from time to time.

Source

 * This article uses material from the Kokushibo on the Kimetsu no Yaiba Wiki and is licensed under the Creative Commons Attribution-Share Alike License.