Shinobu praises Zenitsu for holding out administers the antidote to the spider’s poison, Giyuu ties the injured Inosuku up for his own good, and that’s literally it for those four characters. The remaining runtime is spent exclusively on Tanjirou, Rui, and Nezuko, resulting in Demon Slayer’s finest episode to date.
After getting his head cut by Rui’s threads, Tanjirou tries to get close once again, refusing to take back what he said about Rui’s familial bonds being false. Rui reveals he is one of the Twelve Kizuki and unleashes a web of threads, forcing Nezuko to leap out of her box to shield her brother from wounds that would surely kill him.
This changes the entire complexion of the battle, as Tanjirou is no longer on his own, and now that Rui knows that Tanjirou actually does have such an unassailable bond with his sister, he carries her with him even though she’s now a demon. Naturally, Rui wants that kind of bond, but knows no way of attaining it except by stealing Nezuko.
When both Tanjirou and Nezuko protest and fight back, Rui suspends Nezuko in a web of threads that squeeze her limbs so tightly they threaten to slice her into bits, pulling tighter when she won’t settle down until she passes out.
Of course, Tanjirou can’t bear to see his sister so viciously treated—especially under the guise of Rui asserting his newly-established familial “bond” with her. Tanjirou digs deep into his Water Breathing and manages to unleash the Final Form, which is just enough to slice through Rui’s threads.
The only problem is that the threads are not at their maximum strength, and even if they were, they’re not as tough as Rui’s skin. Tanjirou simply cannot spin the water fast enough to be a considerable threat to Rui; worse, the attempt only makes Rui grow tired of the battle, and he strengthens his threads with his own blood to ensure Tanjirou will get sliced.
With Nezuko out cold and those deadly threads about to close around Tanjirou, his life flashes before his eyes, something Shinobu told Zenitsu earlier could be a person’s way of trying to find some way, any way, of delaying death by looking back on one’s life.
In Tanjirou’s case, he looks back to when he and Nezuko were happy little kids, both watching and imitating their father’s Hinokami (fire god) Kagura dance. Despite being frail, their dad was able to dance beautifully in the freezing cold thanks to a specific type of breathing which, along with his distinctive earrings, he vowed to pass to his eldest son.
Tanjirou only remembers that he has inherited Hinokami Kagura Breathing now because he has to; because otherwise death is imminent. Blue water turns to red fire which Tanjirou uses to slash away Rui’s reinforced threads on his way to the demon’s neck. However, he needs one more push, courtesy of a familial bond Rui doesn’t have, and thus could never truly defeat the Kamados.
That bond is expressed when Tanjirou and Nezuko’s mom urges the unconscious Nezuko to wake up, because she has to save her brother. In another first, Nezuko unleashes her own Blood Demon Art, “Exploding Blood”, which is exactly that. Her blood travels along the threads until it reaches Rui just as Tanjirou makes contact with his neck.
The combined powers of true loving brother and sister successfully decapitate Rui, who never knew what hit him. ufotable pulls out all of the visual and musical stops, from dad’s fluid Kagura dance to the climactic decisive strike. It all plays out like the crescendo of a full-length feature film, complete with epic orchestral score, and transitions into a unique credit sequence with images of the Kamado family united as one.