The battle between Tanjiro Kamado and Nezuko Kamado vs. Rui took place on Natagumo Mountain. It focuses on the battle between Tanjiro Kamado, the demon slayer, and the demoness Nezuko Kamado against the lower rank five Rui.
Tanjiro informs Rui that he has no real family connection, only a false one based on fear, mistrust, and violence, rather than one based on love, kindness, and compassion. This enrages Rui, who then tries to cut Tanjiro up with his sons. Despite his best efforts, Tanjiro manages to avoid the steel wires. Rui then uses a barrage of wires to surround Tanjiro. Tanjiro closes his eyes, expecting to be slashed, but he is not.
Tanjiro and Rui are both taken aback when it is revealed that Nezuko was the one who shielded Tanjiro from the Threads while allowing her body to absorb the full Thread-Cutting Force. Tanjiro screams Nezuko’s name in terror before carrying her to safety. Rui realises the two are related. He is astounded that, despite being a demon, Nezuko protected Tanjiro, a human. Rui realises their connection is genuine. He declares his desire for this link, his eyes twinkling with envy.
The Spider Demon’s daughter, who is listening, begs Rui not to abandon her because she is his big sister. Rui responds by chopping off the girl’s head and telling her to shut up. He then says coldly that she and the rest of the “family” have never fulfilled their roles, not even once. He then tells the girl that if she wants to prove her worth in his eyes, she must go to Mount Natagumo and kill all the Demon Slayers. The girl nods, then lifts her head and exits the stage.
Rui then tries to bargain with Tanjiro, saying he was moved by Tanjiro and Nezuko’s bond. Rui then says that he will let Tanjiro live if he allows him to take Nezuko. Tanjiro refuses right away, claiming that Nezuko is a living being with feelings, emotions, and a heart. Rui then says that’s fine, and that he’ll create a bond of fear between himself and Nezuko. Tanjiro declares that he will never give up Nezuko and will sever Rui’s head. Rui praises Tanjiro’s wit and bravery. He informs Tanjiro that he is in fact Lower Rank 5 among the twelve Kizuki. Rui then expresses his desire to see Tanjiro try to defeat him.
Rui pulls Nezuko to his side, saying that now that he has his sister, Tanjiro’s role is to die. Tanjiro then charges at Rui with his shattered Nichirin Blade. Rui attacks Tanjiro with her threads, while Nezuko tries to escape Rui’s grasp, even scratching his face. Tanjiro notices that Rui is no longer holding Nezuko as he dodges Rui’s attack. A drop of blood falls on Tanjiro’s blade at that precise moment. When he looks up, he sees Nezuko suspended in the air by Rui’s wires, the wires digging into her skin and injuring her severely. Rui claims that because Nezuko is a demon, the threads will not kill her, but that she must be taught a lesson. He goes on to say that if Nezuko doesn’t behave well, he will leave it like that until sunrise so that it is burned and disintegrated. Tanjiro yells at Rui, demanding that he let Nezuko go. Rui then uses his wires to trip Tanjiro and cause him to collapse to the ground. He then kicks Tanjiro in the stomach which sends him flying towards a bush.
Rui then punches Tanjiro repeatedly until Tanjiro has the opportunity to sever Rui’s head. But his blade barely scratches Rui’s neck. Rui declares that Tanjiro has no chance of beating him and kicks him again, causing him to collide with a nearby tree. Witnessing the scene, Nezuko struggles in her shock, screams, and tries to free herself from the wires. Rui tells her she’s making too much noise and asks her to stop. The threads tighten and dig deeper into Nezuko’s skin, causing her to scream in agony as she is further injured. Tanjiro then warns Nezuko not to soften, as doing so would play into Rui’s hands. Nezuko then appears to fall into a sleepy state. Rui notices that Nezuko has a unique aura and is different from other demons. Tanjiro tells himself to calm down and control his breathing. He realises that he must use the final form of Water Breathing to defeat Rui. Tanjiro makes use of Total Concentration: Water Breathing, Tenth Form: Consistent Flow Rui tells himself that he will have problems if this continues. Rui then injects his own blood into his threads, turning them red and amplifying the power to its utmost. Rui applies his Blood Demon Art: Cutting Thread Cage to Tanjiro, completely encircling him. Tanjiro can smell the threads and tells that he can’t cut them with his current strength. Tanjiro employs the Total Concentration: Water Breathing, Tenth Form: Steady Flow technique. Rui tells himself that he will have problems if this continues. Rui then injects his own blood into his threads, turning them red and amplifying the power to its utmost. Rui applies his Blood Demon Art: Cutting Thread Cage to Tanjiro, completely encircling him. Tanjiro can smell the threads and tells that he can’t cut them with his current strength. Tanjiro employs the Total Concentration: Water Breathing, Tenth Form: Steady Flow technique. Rui tells himself that he will have problems if this continues. Rui then injects his own blood into his threads, turning them red and amplifying the power to its utmost. Rui uses his Blood Demon Art: Cutting Thread Cage to Tanjiro which surrounds him completely. Tanjiro can tell by the smell of the threads that he cannot cut them with his current strength.
Thinking he might die from the wires, Tanjiro’s life flashes before his eyes. He then remembers the Hinokami Kagura that his father, Tanjuro Kamado, performed every year on New Year’s Eve. He also remembers what his father told him to make sure that the hanafuda earrings and the Hinokami Kagura would be transmitted to Tanjiro without interruption. Tanjiro remembers the promise he made to his father. Next, Tanjiro switches from Water Breathing to Hinokami Kagura: Dance, with the water dragon gracefully transforming into a burst of fire and sun.The Kamado family’s Breathing Style, which had been passed down through generations, was powerful enough to cut through Rui’s strongest threads. When Rui saw this, he began to panic. As he counterattacked with more wires, he began to pull away from Tanjiro. The battle between the threads and the Hinokami raged on until Tanjiro used his enhanced sense of smell to locate the opening thread. Tanjiro understands that even if he is knocked down by Rui’s sons after the final attack, he must defeat Rui regardless.
Meanwhile, Kie Kamado appears in Nezuko’s consciousness and reaches out to her, pleading with her to help her brother or else he will die. Nezuko then awakens, and she gains access to the Blood Demon Art: Explosive Blood. Nezuko transforms the blood of Rui’s entangled threads into pink and crimson red flames that incinerate the threads about to strike Tanjiro, leaving a few drops of Nezuko’s blood on Tanjiro’s Nichirin Blade. Rui is surprised that the pink flames burned the wires. Tanjiro then drives the scope of his blade into the opening wire. Tanjiro then declares that no one can ever break the bond he has with Nezuko.
As he thus exclaims, Nezuko’s blood drops on the shattered blade turn to fire, and then the heat of the fire is absorbed by the blade, causing the blade’s color to briefly change from black to crimson red. . Tanjiro then separates Rui’s head from his body with his blade, which had combined Tanjiro’s and Nezuko’s powers into one, like the siblings’ hearts were into one.
After the battle, Nezuko is free of Rui’s clutches. She collapses exhausted on the ground. After being forced to switch from water breathing to Hinokami Kagura, Tanjiro also collapses to the ground. As he crawls over to Nezuko, he notices that Rui did not emit the ash smell associated with demon disintegration. It is then revealed that Rui and his sons quickly cut off his head before Tanjiro could. Rui reattaches his head, complaining that Nezuko’s Blood Demon Art hurt him but not Tanjiro. Rui is now even more enraged, and he attempts to finish Tanjiro off with Blood Demon Art: Murderous Eye Basket. Tanjiro is about to be dismembered when he is saved by the Water Hashira Giyu Tomioka.
He then instructs Tanjiro to rest and protect his sister while he handles the rest. Rui, enraged that other Demon Slayers have appeared, prepares his most powerful attack: Sharp Thread Spin, Blood Demon Art. Giyu employs Total Focus: Eleventh Form: Dead Calm Water Breathing to block it, negating the attack. Rui is taken aback when Giyu cancels his most powerful attack without even trying. He tries to attack Giyu with other threads, but Giyu cuts off Rui’s head in a single gash and removes the Lower Ranks’ blood with the Chiburi process before he can. Rui was stunned, unable to believe what had just occurred. Rui then turns to ash as he tries to reach Tanjiro and Nezuko, with Tanjiro putting his hand on Ruis dress.