Kyojuro Rengoku/Synopsis

History
Kyojuro was the eldest son of Shinjuro Rengoku. His father was known as the Flame Hashira of the Demon Slayer Corps until his unexpected retirement. Kyojuro also had a younger brother who trained alongside him until their father ceased to teach them.

Rehabilitation Training Arc
Kyojuro is present with his fellow Hashira when Tanjiro Kamado awakens.

Shinobu Kocho notes that Tanjiro is on trial, for which Kyojuro sees no need for as he was protecting a Demon, which is a clear violation of conduct; he states that it was a matter they could deal with themselves. He then agrees with Gyomei Himejima's idea to kill Nezuko Kamado, witnessing shortly afterward Tanjiro's coughing fit, and remains silent when Mitsuri Kanroji asks if they should be dealing with their subordinate's trial without Kagaya Ubuyashiki's input. After Tanjiro headbutts Sanemi Shinazugawa, Kyojuro looks at Mitsuri when she laughs with a neutral expression.

Mugen Train Arc
Kyojuro is sent to investigate a series of brutal attacks plaguing a small village, believing it to be related to the incident surrounding the disappearance of forty passengers aboard the Mugen train. He meets with another demon slayer at a ramen shop and they discuss their next plan of action, to which he is informed the Mugen Train is being held at a maintenance facility after being put out of service. After finishing their meal, they set off to a nearby train station. They encounter a young girl, Fuku, saddened by the lack of customers buying her bento boxes as the news of the attacks is scaring everyone into staying inside after dark. Kyojuro unabashedly tells her he is looking for a demon, to which she angrily hurls her bean bun and retorts that demons don't exist. However, he is unfazed by her actions. After being calmed by her grandmother, Fuku apologizes and asks if he would like to buy some bento boxes. He happily buys them all and gives them to his companion, telling him to return to the Demon Slayer Corps. as the bentos will make great gifts.

Kyojuro, carrying a crate of bento boxes, boards a train headed for maintenance, believing he will be taken to the same facility as the Mugen train. After being confronted by a train conductor and told the Mugen train's actual location, he leaps off the train and heads to the repair shed. There, he sees the train and senses the faint scent of a demon, confirming a demon is responsible for the disappearances. He is met by a worker, to whom Kyojuro claims he was sent to the facility and give the workers the bento boxes. As the workers eat, Kyojuro is told the train is being repaired and will be put back into service again, unnerving him. Suddenly, a scream is heard, forcing Kyojuro to confront the situation. A marked demon appears, responsible for the attacks reported, clutching a young worker in his claws and causing him to bleed heavily. Kyojuro tells the culprit to surrender him, but the demon tells him human food disgusts him now, stepping on a bento box, to which he adds that he only eats humans he find palpable and kills the ones he doesn't.

The demon activates his Blood Demon Art, enabling him to speed around the Hashira and taunt him. Kyojuro acknowledges his speed but warns him to not get cocky facing him. He informs the demon the woman he attacked is slated to make a full recovery, angering him. Seeing the destroyed bento box, the demon decides to kill the bento vendors to spite Kyojuro. He tries to kill the worker, but Kyojuro slices off both his hands and forces him to retreat. After treating the boy's injuries, he is met with other demon slayers, telling them to take charge here while he confronts the demon. Kyojuro heads towards the demon's trail and follows the train tracks, using his Total Concentration Breathing to accelerate him to incredible speeds. The demon finds Fuku and tries to kill her but is momentarily distracted by Fuku's grandmother. Fuku tries to escape but he catches her outside and tries to crush her throat. Kyojuro arrives in time, slices the demon's achilles and saves Fuku.

He confronts him again as he tries to kill Fuku's grandmother, repeating his words not to get cocky. The demon tries to challenge him over who is truly faster; if he is able to kill him before he kills her. To which Kyojuro responds that the challenge is unnecessary. He mocks the demon for being slow and rushes forward instantly, decapitating the unsuspecting demon with his Flame Breathing, First Form: Unknowing Fire. The scene reminds Fuku's grandmother of when she herself was saved by the Flame Hashira, recognizing Kyojuro's haori and manner of sheathing his blade. To this, Kyojuro states that it was likely his father Shinjuro who saved her; he is simply following in his footsteps to save people from demons. As Kakushi arrive on the scene, Kyojuro confirms the demon is dead and the Mugen train will be repaired for service the next day. When his companion expressed relief that the situation finally over, the Hashira adds that it was likely a more powerful demon that what he just faced that is responsible for the train's disappearance.

As the sun sets, Kyojuro boards the Mugen train for his investigation when he meets Fuku and her grandmother again. They offer beef pot bento boxes in gratitude for his heroic actions, to which he happily accepts and takes Fuku's entire stock. The two bid him good luck on his mission and the train leaves the station.

During the journey, while devouring his eleventh bento box while shouting "delicious," Tanjiro, who was told to meet him, introduces the Hashira to Inosuke Hashibira, Zenitsu Agatsuma and Nezuko, who he recognizes during Tanjiro's trial with the Master. After he finishes his food and Tanjiro explains his question about Hinokami Kagura, Kyojuro energetically answers that he doesn't know what Hinokami Kagura is and that this is his first time hearing about it. He says that he's delighted that Tanjiro applied his father's dance to his fighting style, then swiftly changes the subject and tells Tanjiro that he should become his Tsuguko. Tanjiro tells him to slow down and asks if he can at least try and help a little more to answer his question.

Kyojuro says that Flame Breathing has a long history, and says that there has always been a Hashira in every age who uses Water Breathing and one who uses Flame Breathing. He explains that the other Breathing Styles were derived from either those two or Wind Breathing, Stone or Thunder. Kyojuro then asks Tanjiro what color his Nichirin Sword is, to which the latter responds that it's black, and Kyojuro laughs out and says that that must be unfortunate. Tanjiro asks why that is, and, as the train starts to take off, Kyojuro explains that he's simply never seen a swordsman with a black blade become a Hashira before, and that he's heard people whose blades turn black don't even know which Breathing Style to master. Seeing Tanjiro's face, he tells him not to worry and that he'll train him up back at his house.

The conductor then comes over to the four of them to stamp their tickets. Tanjiro smells something unusual, and Kyojuro appears to sense it too as he asks the conductor to step aside, simultaneously preparing his sword. A large-bodied demon appears at the other end of the carriage, and Kyojuro wonders if it was hiding with its Blood Demon Art unbeknownst to him ,before darting forward to behead it with the Flame Breathing, First Form: Unknowing Fire. The demon's dead body falls to the floor, only for Kyojuro to add that a second one is nearby, prompting Tanjiro and Inosuke to follow him. As the frightened crowd flee to another carriage, they find the demon cornering a single passenger, leading Inosuke to charge ahead and ignoring the two. When he is nearly hit by its long arms, Kyojuro rushes forward to save Inosuke and the passenger, before using his Flame Breathing, Second Form: Rising Scorching Sun to kill it. An amazed Tanjiro, Inosuke and Zenitsu all declare they would love to be his Tsuguko, leading him to laugh and state that he would gladly train them all.

Sometime later, when the four are all asleep, Kyojuro dreams that he's back at his house, telling his father, Shinjuro, about his promotion to Hashira. Shinjuro dismisses him, saying it's pointless and doesn't matter because neither Kyojuro or himself will ever become great people anyway. Kyojuro gets up and walks out of the house, out into the garden, his little brother, Senjuro, coming to greet him and asking if their father was happy about the news and wondering if he would acknowledge him too if he also becomes a Hashira. Kyojuro remembers how his father used to be, a happy man who was passionate about training his children as swordsmen, and how he changed after their mother's death.

He admits to his brother that Shinjuro wasn't happy to hear the news, but enthusiastically adds that his passion won't die because of that and that he'll never be disheartened. Senjuro still looks upset, but his big brother comforts him, saying Senjuro's not like him because he has an older brother to look out for him. He reassures him that whatever path he takes, he'll be a wonderful person, and, as Kyojuro hugs his brother, he tells him to do his best and keep on living, no matter what.

Still within the dream, Kyojuro begins to tutor Senjuro in his sword skills. In reality, a young girl, who's working for Enmu, ties her wrist to his unconscious body with a special piece of rope that was made by the Upper Moon, allowing her to enter Kyojuro's dream. Enmu has sent her in to destroy Kyojuro's spiritual core, which, when destroyed, would render him a lifeless shell unable to put up a fight against the Demon. The spiritual core lies in the area of unconsciousness just outside of Kyojuro's dream realm, and she quickly slips past him and Senjuro without either noticing. She finds his subconscious realm, which lies past the wall surrounding his garden, and breaks into it, only to find herself in an unusually hot and flame-ridden one.

The girl locates his spiritual core, but, as she goes to break it, she is suddenly lifted tightly by the neck by an invisible force. On the train, Kyojuro grabs her throat but remains unconscious, his survival instinsts enabling his body to sense the threat and stop it. But with the two still unconscious, they are locked together.

Tanjiro soon wakes up from the dream he was having and asks Nezuko to burn the rope connecting Kyojuro and the girl, removing the girl from the Hashira's dream. After the young Demon Slayer's confrontation with Enmu, Kyojuro too wakes up and tells Tanjiro that he, Zenitsu and Nezuko will defend the eight train cars from the Demon while Tanjiro and Inosuke go down to the front of the train to defeat him.

After Tanjiro and Inosuke have successfully defeated Enmu and escaped the out of control Demon train with Nezuko, Zenitsu and Kyojuro, the Hashira checks on an injured Tanjiro as Inosuke goes to rescue another passenger. He applauds the young Demon Slayer for his recently-acquired ability to use Total Concentration Breathing all the time, and says that this is the first step to him becoming a Hashira.

Kyojuro then notices that Tanjiro is bleeding from the abdomen and tells him to focus his breathing in order to heal himself, which the young Demon Slayer manages with some guidance from Kyojuro. The Flame Hashira tells Tanjiro that if he can master his breathing, he'll be able to accomplish many more things and become stronger tomorrow than he was yesterday. Just as Kyojuro starts to tell Tanjiro that he doesn't need to push himself any further because everyone's been saved, something jumps down just behind the two Demon Slayers with a great force, scattering the dust around them.

The dust clears to reveal Upper Rank Three, who immediately launches himself towards Tanjiro with the intention of killing him, but is stopped by Kyojuro's Flame Breathing, Second Form: Rising Scorching Sun attack, causing him to leap backwards, away from the Demon Slayers.

The Demon immediately regenerates his injuries and compliments Kyojuro's katana. The Hashira asks him why he was targeting an injured person, to which the Upper Rank says that he thought Tanjiro would get in the way. Kyojuro asks if they have any business together and that he already hates the Demon, despite it being their first time meeting, and the Demon says that he hates weak humans too. The Upper Rank then asks Kyojuro if he wants to be a Demon too.

Kyojuro swiftly declines, but the Upper Rank persists. Kyojuro says that he is the Flame Hashira, Kyojuro Rengoku, and the Demon introduces himself as Akaza. Akaza keeps persisting, saying that Kyojuro would have more time to get stronger as a Demon than a human since he wouldn't have to worry about death.

Kyojuro says that dying is the very beauty of being human, and that he thinks it is the reason that humans are so unique and precious. He says that Akaza shouldn't insult Tanjiro and that he is not weak, and then says that he will never become a Demon. As he begins to use Technique Development, Destructive Death: Compass Needle, Akaza says that he will just kill Kyojuro if he won't become a Demon. He attacks Kyojuro as the Hashira runs towards him with his Flame Breathing, First Form: Unknowing Fire attack readied. Akaza jumps back, and says that none of the Hashira he's killed have ever agreed to his invitation to become a Demon and that he finds that hard to understand. He tells Kyojuro to die now, while he's young and strong.

Akaza unleashes Destructive Death, Air Type, which Kyojuro counters with Flame Breathing, Fourth Form: Blooming Flame Undulation. The Hashira notes that Akaza is attacking him from a distance, punching into the air and moving at a fraction of a blink, and realizes that he'll have to get closer to him if he's to defeat him. Kyojuro suddenly appears in front of Akaza, who compliments his reaction speed as the Hashira attacks him with his flames. The Upper Rank praises his sword skills, and wonders to Kyojuro how sad it'll be if they're lost early, to which the Hashira replies that it won't be sad because it's only natural for people to die.

Tanjiro begins to get up, wanting to help the Hashira out, but Kyojuro tells him to stay where he is, because his wound could be fatal if reopened. Akaza tells him not to take notice of "the weaklings" and to focus on who he's fighting and Kyojuro, angered, attacks the Demon with Flame Breathing, Fifth Form: Flame Tiger as Akaza unleashes his Destructive Death, Disorder. The residue stirred by their attacks clears, and Akaza tells Kyojuro, who's now bloodied and beaten, not to die on him just yet. Tanjiro and Inosuke panic, the latter wanting to jump in to help Kyojuro but soon realizing that he'd only be a hindrance, as the Hashira and Upper Rank seem to be in an entirely different dimension to him. Akaza says that Kyojuro fighting with his body is pointless since he can't heal his wounds instantly like a Demon, and that humans will never be able to defeat Demons.

Tanjiro tries to pick himself up to go and help Kyojuro, but is unable to generate any strength into his limbs because of the aftermath of the Hinokami Kagura, which he used to defeat Enmu. Kyojuro turns back to face Akaza, smiling and saying that he'll fulfil his duties before beginning to ready another attack. Impressed, Akaza compliments his fighting spirit and technique, and laughs as he says that Kyojuro really should've chosen to become a Demon, asking the Hashira to fight with him for all eternity.

The two clash again, Flame Breathing: Ninth Form - Rengoku meeting Destructive Death: Annihilation Type, and the dust this time disperses to reveal that Akaza has stuck his arm through Kyojuro's stomach. Akaza screams that he's going to die, and asks Kyojuro one more time to become a Demon.

This causes Kyojuro to remember his mother, Ruka, and a flashback shows one of their final moments together. Ruka asks a younger Kyojuro if he knows why he was born stronger than other people, and asks him to think hard about this question. Kyojuro ponders this for a while, then barks out that he doesn't know the answer. Ruka explains that he was given such strength to protect the weak, and that power should be used for the world and for the people, not for abusing it in order to hurt others. Ruka hugs Kyojuro to her chest and, as she begins to cry, tells him that, even though she won't be alive much longer, it was a blessing for her to have been the mother of such a strong, gentle child.

Now back in the present, as he summons the last of his strength to swing his sword into Akaza's neck, Kyojuro thanks Ruka as well for being his mother. Kyojuro lets out a shout as he drives his sword deeper in, and, as Akaza tries to hit him with a punch to the face, the Hashira grabs his wrist and stops the attack before it reaches him. Akaza is incredibly impressed by Kyojuro's strength, and then he looks behind Kyojuro and begins to panic as he realizes that the sun is about to come up. Akaza tries to free himself from Kyojuro's hold, but the Hashira holds on tightly to his wrist, not letting him escape.

Tanjiro finally finds the strength to pick up his sword, and starts to run over towards the pair with the intention of dealing the finishing blow to Akaza. With a loud shout of effort, Akaza tries again to pull himself away from Kyojuro, but he fails again as Kyojuro's blade moves deeper into Akaza's neck. Tanjiro yells to Inosuke to move for Kyojuro's sake, and, just as the boar-headed Demon Slayer readies his Beast Breathing: First Fang - Pierce, Akaza manages to pull himself away from Kyojuro.

The Upper Rank quickly jumps backwards, both of his arms now severed, and runs into the forest beside where they'd been fighting, leaving Kyojuro to fall onto his knees, defeated. As the Demon retreats, Tanjiro throws his sword at Akaza, screaming at him not to run away from the fight and calling him a coward. The young Demon Slayer yells that Kyojuro is better than Akaza will ever be because he fought until the end and didn't let anyone die, and that Kyojuro was the rightful winner of their fight.

Tanjiro lets out a final scream and collapses to his knees, crying, and Inosuke starts to shake. Kyojuro looks over at him and smiles, telling Tanjiro to come over to him so they can have a final chat before he dies. Kyojuro tells Tanjiro that he should try to visit Rengoku House if he wants to learn more about Hinokami Kagura, since he remembered that his father had some notes that had been left behind by the Flame Hashira who came before he and his son. Tanjiro tells Kyojuro that that's enough, and asks him if there's any way for him to recover from the injuries Akaza inflicted on him, to which he says there isn't and asks Tanjiro to hear him out while he can still talk. Kyojuro asks him to tell his little brother Senjuro that he should proceed down the path his heart tells him to, the one he thinks is right, and to tell his father to take care of himself. He then looks Tanjiro in the eye and tells him that he believes in Nezuko, and fully accepts her as a member of the Demon Slayer Corps after seeing her protect so many humans on the Demon train.

Kyojuro tells Tanjiro to live with his head held high and that he shouldn't worry about him dying here, since it's only natural for a Hashira to give his life protecting his junior. He looks to Tanjiro, then to Inosuke and to Zenitsu, and says that he believes in them and that he thinks they will become the next generation of Hashira of the Demon Slayer Corps.

The Flame Hashira then sees the spirit of his mother in front of him, and asks her if he did well, to which she replies that he did a wonderful job. As the last seconds of his life slip away, Kyojuro smiles.