Muichiro Tokito, Genya Shinazugawa, Sanemi Shinazugawa and Gyomei Himejima vs Kokushibo

Muichiro Tokito, Genya Shinazugawa, Sanemi Shinazugawa and Gyomei Himejima vs Kokushibo is a battle that takes place in the Infinity Castle, that occurs between Demon Slayer Genya Shinazugawa and three Hashira, Muichiro Tokito, Sanemi Shinazugawa and Gyomei Himejima against Upper Rank 1, Kokushibo.

Prologue
Muichiro Tokito is separated from Gyomei Himejima by Upper Rank 4 Nakime's Blood Demon Art in which she manipulates a large column of the Infinity Castle and warps an opening to where Muichiro is teleported to where another Upper Rank is residing. As Muichiro is getting back up, he sees a petrifying six-eyed figure in front of him with a purple and black hexagonal patterend kimono and a long sword. The figure gazes at Muichiro and discerns that the Hashira is of familiarity to him. Muichiro sees the Kanji for Upper Rank as well as the kanji for One, realizing that he looking at the infamous Upper Rank 1, Kokushibo in the flesh. Kokushibo sees the muscles, ribs and blood flow of Muichiro identical to how Tanjiro saw that of Akaza and Giyu and determines that Muichiro is of similar blood to him. Muichiro on the other hand perceives that Upper Moon 1 is far more terrifying, dignified and majestic compared to any other Twelve Kizuki member as well as him having a sword similar to the Nichirin Blades believing that Upper Rank 1 was once a Demon Slayer. As he grabs the hilt of his sheathed sword, Muichiro's body begins to tremble due to the Upper Rank's horrifying aura despite this never happening once in his life. The Upper Rank asks the Hashira of his name, in which he stutters it out loud. Kokushibo finds out that the 'Tsugikuni' name has died out and is no more. This perplexes Muichiro as he has never heard the name Tsugikuni once and asks the Upper Rank what Tsugikuni is. Because of hundreds of years passing, Kokushibo knew that it was inevitable for his family name to die out in which he says out loud to be 'Michikatsu Tsugikuni'. He also states that he is a descendent of one of his chidren, thus making him his literal offspring. This greatly horrifies Muichiro that he is related in blood to an Upper Rank, thus him questioning if Kokushibo is a user of the Sun Breathing, the first Breathing Style. However, Muichiro attempts to calm himself down with his breathing which makes Kokushibo praise his mentality. Muichiro quickly dashes toward the Upper Rank, thus the battle begins.

Battle
Muichiro attempts to behead Kokushibo with his Mist Breathing: Second Form - Eight-Layered Mist. The Upper Rank however dodges it elegantly and admires Muichiro's swordsmanship skills along with realizing that his descendant uses the Mist Breathing. Muichiro is not interested in another conversation with his so-called "ancestor" in the slightest and unleashes his Mist Breathing: Fifth Form - Sea of Clouds and Haze on the Upper Rank who which evades the attack again with no difficulty. Kokushibo calls Muichiro's name and that despite his incredibly young age of 14, his swordsmanship skills are this refined and beautiful.

Connection through Blood
Muichiro says that despite him being his descendant, over the hundreds of years that have passed no drop of blood of them are connected anymore. As he is giving his articulation to Kokushibo, his Demon Slayer Mark appears once again to which catches the Upper Rank by surprise. Muichiro finally unleashes his original Mist Breathing: Seventh Form - Obscuring Clouds on the Upper Rank, in which he has never seen in the hundreds of years of him fighting numerous Mist Breathing users. Unfortunately, the Upper Rank evades the attack once more. Kokushibo finally decides to unsheathe his sword due to it going against his samurai code of respect and uses his Moon Breathing: First Form - Dark Moon — Evening Palace on the Mist Hashira. Muichiro sees his left hand cut off from the attack, and realizes that Upper Rank 1 utilizes a Breathing Style he has never seen, Moon Breathing. He also notes that Kokushibo's speed is in another dimension, him not even being able to react to his attack. Muichiro however still fights on and bites a strand of his hair in order to stop the hemorrhaging, in which Kokushibo praises him for. He uses the Mist Breathing: Fourth Form - Shifting Flow Slash in order to behead Kokushibo, but instead the Upper Rank grabs the Hashira's blade with his fingers and redirects the angle of the attack to stab Muichiro with his own sword through a column. As Muichiro exclaims in pain, Kokushibo requests him to become a Demon so he may become a member of the Twelve Kizuki, possibly an Upper Rank. The Upper Rank is moved that he has witnessed a descendant of his own cells after the centuries of living. He tells Muichiro that there is nothing to fear anymore once he is a demon. His arm would easily regrow and due to Kokushibo being the remaining Upper Rank to properly fight at the moment, he is certain that Muzan Kibutsuji would find some use of a Demon Slayer becoming a Demon. If he doesn't, he then wants Muichiro to accept his death as his fate. Thus proving that no matter how much one may try, they can only go so far. Genya is shown behind a curtain with a Nichirin Blade and his traditional western double-barreled shotgun. As he was about to pull the trigger, Kokushibo is seen right behind Genya and questions him if he agrees or not. Doing so, Genya's arm wielding his shotgun falls off his body with Muichiro screaming his name at the top of his lungs. Genya quickly draws his Nichirin Blade from his back but to no avail as his remaining arm gets cut clean off by Kokushibo. Kokushibo sees Genya's cellular structure realizing that he is a Demon Slayer who doesn't use any Breathing Style but rather consumes demons as his source of strength, thus making him have similar regeneration to one as well. With no hesitation, Kokushibo intentionally cuts Genya's torso in half with Muichiro knowing that Genya will be killed by his ancestor while not even wanting him to fully turn into a demon.

Brothers in Arms
Kokushibo is surprised that Genya is not dead by his wounds even when he specifically went for the kill. He says that he met a Demon Slayer three centuries ago that ate Demons like Genya and killed him by slashing his torso. Since Kokushibo knows that any and all Demon consuming Demon Slayer have to have a vulnerable spot, he goes ahead and goes to decapitate Genya. Suddenly, Genya's brother Sanemi rescues him by reflecting the Upper Rank's attack with Wind Breathing: Fourth Form - Rising Dust Storm. Kokushibo makes his distance and sees that the Wind Hashira, Sanemi Shinazugawa has come in his prescene. Sanemi agrees with the Upper Rank that he is indeed the Wind Hashira and that he'll be the wind that'll rip off his head. The Wind Hashira asks his younger brother as to why he would murder their own mother, in order to protect him. As Sanemi explains this, Genya remembers when Tanjiro told him that despite Sanemi being angry at him for joining the Demon Slayer Corps, he never had a scent of hatred from him. As a result, Genya should have no fear of saying anything to his brother. Sanemi tells Genya that he should've never joined the Demon Slayer Corps and that he should've had a wife and children. And if he did so, Sanemi would've never let a demon take them away from him. This makes Genya shed tears as Sanemi expresses his true feelings towards him. Kokushibo sees the tranquility between the two Demon Slayer brothers as it gives him nostalgia for his own younger brother. Sanemi shouts in anger at the Upper Rank for him slicing his younger brother. He dashes at Kokushibo while the Upper Rank attempts to behead him but Sanemi slides underneath his legs in order to slash them off. As Kokushibo jumps into the air, Sanemi uses Wind Breathing: First Form - Dust Whirlwind Cutter in which Kokushibo draws his sword in order to block the attack. Sanemi is disgusted by Kokushibo's blade filled with flesh and eyes.

Breath of the Moon
As both of their swords clash, Kokushibo uses the Moon Breathing: Fifth Form - Moon Spirit Calamitous Eddy on Sanemi, forcing him to backstep away from the attack. However Sanemi is confused as to how so many slashes are appearing even when the Upper Rank isn't swinging his blade. Sanemi counters Kokushibo's attack with Wind Breathing: Third Form - Clear Storm Wind Tree which he praises both Sanemi and their attacks for being at their absolute peak. Sanemi thinks to himself that he can't stop getting goosebumps at Kokushibo's overall prowess and skill. He comes to the conclusion that Kokushibo's slashes are surrounded by miniature chaotic slashes that constantly change in change in size and length, thus making them have no set pattern making them even more deadly. He knows that he can't ward off the Upper Rank's attack completely due to its sporadic and warped behavior, and that if he didn't have the experience of a Hashira and a Demon Slayer it would be absolutely impossible for him to defend himself. And most of all, he uses Breathing Styles and that his speed and strength is still rising as he is still speaking. Thus Sanemi is having a lot of fun and that Kokushibo is a demon worth killing with pride. Sanemi assaults Kokushibo with Wind Breathing: Second Form - Claws—Purifying Wind to which the Upper Rank reflects it off with a basic attack with the chaotic blades. As he was reflecting the Breathing attack, Sanemi falls from the air attempting to cut Kokushibo but fails as he blocks it with his flesh sword. He comes to Kokushibo's surprise as Sanemi attempts to stab him with Genya's Nichirin Blade through his chin. The Upper Rank elegantly dodges the blade and slashes it off Sanemi's foot. As Sanemi and Kokushibo keep clashing, Sanemi notes that he can't even blink once and that he was near death due to him nearly mispositioning the tip of his blade, Kokushibo praises Sanemi which reminds him of the Wind Hashira during the Sengoku Period, proving that he either sparred against the former Hashira or killed him. He then overwhelms Sanemi with his Moon Breathing: Sixth Form - Perpetual Night, Lonely Moon — Incessant which knocks him back along with decimating the surrounding landscape.

Cats to Silvervine, Demons to Marechi
Sanemi is revealed to be heavily wounded with his torso having gaping wounds. Kokushibo venerates Sanemi's ambition and his desire to fight but knows that his internal organs will disgorge all over the floor if he moves anymore. Suddenly, Kokushibo's heart rate increases and he begins to stagger. Sanemi begins chuckling as his blood even affects the highest of the Upper Ranks of the Twelve Kizuki and compares the irresistibility of his blood to demons like cats to silvervine. He even says that Demons receive a drunken effect just from taking a whiff of his own blood, with it being the rarest of the rare and once in a lifetime. Sanemi continues to attack with Wind Breathing: Sixth Form - Black Wind Mountain Mist to Kokushibo's surprise as despite his near life-threatening wounds he still continues to engage in combat. Kokushibo even states that if he fought any other Hashira, they would certainly die if they had the same injuries as what Sanemi has. This comes to the conclusion that Sanemi is barely even human. Kokushibo then steps on Sanemi's Nichirin Blade and slashes downward toward the Hashira. Sanemi blocks Kokushibo's attack from hitting him with Genya's western shotgun and fires it at the Upper Rank but to no avail as he reflects all the bullets with his flesh sword. Kokushibo then uses the Moon Breathing: Third Form - Loathsome Moon — Chains on Sanemi. As the dust clears, Sanemi is nowhere to be seen and Gyomei Himejima appears and says that the Demon Slayer Corps will never stop until all demons are eradicated from the world. He immediately tells Sanemi to stitch his stomach wound and to stay out of the fight until he finishes. Kokushibo accesses the "Transparent World" to see Gyomei's structure and says that he is the greatest swordsman he has fought in three centuries. Gyomei keeps swinging his flail to gain more momentum and strikes it onto the ground where Kokushibo stood, to which he attempts to use a Moon Breathing attack but Gyomei's chained axe comes after and Gyomei uses the Stone Breathing: Second Form - Upper Smash. As Kokushibo dodges the spiked flail, the chains surround his neck and Kokushibo tries to cut the chains with his sword but fails. As the chains nearly close, Kokushibo ducks down and they only catch a small strand of hair and says that the ball and chain are made of pure iron and that it is an extremely high-grade weapon. Kokushibo's sword is made out of his own flesh so if he tries to cut the chains his sword will burn out before cutting it.

Clash of the Titans
Kokushibo even says that iron that absorbed sunlight to that extent wasn't discovered during the Sengoku Period where both swordsmithing techniques and the Demon Slayer Corps' might were at their absolute peak. Thus in order for him to not be able to get its full extent of damage, he goes close to Gyomei in order for him to not harm himself. Both Kokushibo and Gyomei use their respective Breathing Styles and collide with Moon Breathing: Second Form - Pearl Flowers Moongazing and Stone Breathing: Fourth Form - Volcanic Rock — Rapid Conquest. After the clash with their Breathing Styles, Kokushibo states that when his sword breaks it'll regenerate immediately, thus making all of his attacks completely pointless and pitiful. Gyomei however does not care in the slightest, he crosses his arms and wishes he saved something for when he faces against Muzan Kibutsuji but knows that now he has nothing to lose using it in this dire situation, thus his Demon Slayer Mark is awakened. Meanwhile, Muichiro finally unpins himself from the column that Kokushibo stabbed him to and pulls out his Nichirin Blade from his shoulder. Doing so, he shames his body for not being as durable as Tengen Uzui's and knows that he only has a few hours left until he dies from his wounds if he doesn't get any special treatment which none are around. Knowning his, he decides that if he dies will give it his all and lessen the burden for the other Hashira that are fighting the Upper Rank. He grabs the bandages that Kokushibo covers his torso with when he requested him to become a demon and covers his amputated hand. He picks up his Nichirin Blade and just as he was about to join in on the fight with Gyomei, Genya shouts out his name and appeals him to get the strand of hair of Kokushibo when Gyomei used Stone Breathing: Second Form. He says to Muichiro that he wants to protect his older brother at all costs and to fight until the very end, to which Muichiro completely agrees and joins Genya.

The Price to Pay
Kokushibo on the other hand notices that Gyomei awakened his Demon Slayer Mark and pities him, to the Stone Hashira's confusion. From him glancing at Gyomei, especially with the "Transparent World", he assumes that Gyomei's age is around 27 which still comes to his confusion. Kokushibo then explains that those who awaken their Demon Slayer Mark will die before they see the age of 25. He says that despite the mark increasing one's power, it exchanges them of their own lifespan. Kokushibo laments the Stone Hashira for him mastering his Breathing techniques and bodily functions to his highest degree and that they will disappear without a trace forever due to him unlocking the Demon Slayer Mark. He questions Gyomei that if he also believes that it is tragic as well, to which he disagrees. Gyomei elucidates that that information is old news and is outdated, he even accepts that due to him being a member of the Demon Slayer Corps there is no guarantee that he will see tomorrow even if he didn't awaken his mark. Gyomei finally demands Kokushibo to not promote his moronic notions to others, along with him reminding Kokushibo that there was an individual who bore a Demon Slayer Mark and lived past the age of 25. Angered by the demon underestimating his resolve, he again engages the Upper Rank. Meanwhile, Sanemi, who was able to patch up his torso injuries, also awakens his Demon Slayer Mark and enters combat with Gyomei.

Side by Side
Kokushibo perceives that Sanemi has awakened his Demon Slayer Mark and questions if all the Hashira have awakened their Mark as well, if the Golden Age of the Demon Slayer Corps has been revived. Suddenly, Gyomei's spiked flail came behind Sanemi's head nearly catching Kokushibo by surprise, Sanemi takes this chance to then go for the Upper Rank's calves which he dodges. Kokushibo praises the Hashira even more due to their coordinated assaults despite them utilizing different Breathing Styles. Sanemi openly expresses his gratitude to Gyomei for them both sparring each other during their Hashira training.

Genya meanwhile as he consumes the strands of hair of Kokushibo, feels his body coming together near instantaneously. He also remembers that a chunk of Kokushibo's sword was separated by Gyomei and wonders how much more power he can achieve by consuming that as well but hears Muzan's faint voice again and questions if he is progressing more into a real demon. Kokushibo commends that two different Hashira using completely different Breathing Styles can combine their attacks in order to increase the devastation of their offensive capabilities. It is shown that Gyomei being blind uses a peculiar chained weapon in order to detect the rattling echoes from his chains. The Upper Rank thus swings his sword towards the blunt side of Sanemi's Nichirin Blade in order to break it, Sanemi however quickly reacts and righted his blade so it nullifies the impact from his strike. With the Upper Moon's sword temporarily stuck, the two Hashira continue their offensive. Sanemi distracts the Demon with Dust Whirlwind Cutter, then both Slayers combine their Wind Breathing: Seventh Form - Gale - Sudden Gusts and Stone Breathing: First Form - Serpentinite Bipolar, managing to tear off Kokushibo's kimono. However, the two are suddenly injured by a mysterious attack. The Demon mocks them, saying that ripping clothes can't kill even an infant, before revealing his sword's hidden power: the ability to extend and branch its blades.

The Power of a Weakling
Now enraged, Kokushibo increases the ferocity of his attacks, and the Hashira, despite having their Marks unlocked, are being pushed back. Sanemi and Gyomei barely escape the onslaught, the former losing his index and middle fingers in the process.

When asked, Kiriya Ubuyashiki, does not opt to send help to the four fighters, trusting them to defeat the second most powerful Demon in existence.

Back in the battlefield, Kokushibo continues his relentless onslaught, launching consecutive Moon Breathing attacks: Seventh Form: Mirror of Misfortune - Moonlit, Eighth Form: Moon-Dragon Ringtail and Ninth Form: Waning Moonswaths. The barrage further injures the Wind and Stone Hashira, and the former is almost finished off by Tenth Form: Drilling Slashes - Moon Through Bamboo Leaves but is saved at the last second by a recovered Muichiro, whose wounds were patched up by Genya. As the three Hashira return to battle, Genya, mulling over Tanjirou's words that the weakest fighters have the highest potential to turn the tides of the fight, takes Kokushibo's discarded demonic blade and swallows it.

Aftermath
Kokushibo fades, his soul leaving for hell, with his brother's flute being left behind alongside his clothes. Both Genya and Tokito succumb to their injuries; Gyomei closes the Hashira's eyes and vows to complete their mission to defeat Muzan, while Sanemi breaks down crying as his brother fades away as a demon due to the injuries. Gyomei interrupts Sanemi's grieving, telling him that the night isn't over and that Muzan still has to be defeated.