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 passes 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. 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.